t14811 · IC radio chip £1.05. Extra parts and peb for radio £3.85. Case LI. Send s.a.e. for free...

Easy to build projects for everyone

t14811I tij4E;*

VISUAL

CONTINUITY '-TESTER 4

Australia 75c New Zealaul 75c South Africa 70c Malaysia $2 25

You need never bu a colour film again!Acktbe Everyday Electronics Colour Print Servic3

Kodak colour filmSEND NO MONEYsee your printsbefore you payRELIABLEfilm serviceLUXURY colour printswith a borderlesshi -definitionsheen finish

So it can now cost you les, to takephotographs and, thanks to ourreliable developing and printingservice, you don't send your moneyuntil you've actually seen your pictures.

Hundreds of thousands of magazinereaders are delighted with this out-standing Colour Print service. So whydon't you give it a try?HERE'S WHAT YOU DO

Send us any make of colour printfilm inside the envelope enclosed in thisissue. Or fill in the double couponbelow and send it with your film in astrong envelope to: The EverydayElectronics Colour Print Service.FREEPOST, Teddington, Middlesex,TW11 I BR. No stamp is required.FREE KODAK COLOUR FILM

In return you will receive a freeKodak colour film worth over £1, thesame size as the one you sent us fordeveloping. Meanwhile we produceyour prints, every one of which will bechecked by professionals at ourlaboratories before being sent to you.

You'll love the quality all crisp,sharp, hi -definition sheen prints, andborderless to give you maximum

area.

ats* on Stan d Terms o

UNBEATABLE FOR QUALITY AND ALAWhat about our prices? Certainly

much less than you pay in most r hops,and remember you get anodic- filmFREE. With our Colour Print service,you only pay 14p for each print, plus85p towards developing. postage andpacking. The minimum charge .s 85p(assuming no prints can be made) inc.VAT. The offer is limited to UK Eire,Cl and BFPO.A SERVICE TO BENEFIT YOU

You benefit in two additional ways.Firstly, you enjoy 'a personal service,with every care taken over eachindividual order. And secondly, youpay only for what you get ;- with nocredit vouchers like many othercompanies. An invoice comes withyour prints, so it's a straight businesstransaction.

mailable on request

Cu these labels if you hasn't tot an enyelope. or pass themto a fiend who migut like to take adtantage of our offer.

From: Everyday Electronics Colour Print Service,Freepost, Teddington, Middlesex TW I I I BR

Mr/Ms

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L Postcode

PLEASE FILL INBOTH LABELS

This labelused tosend yourprints

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send yourfree film

From: Everyday Electronics Colour Print Service,Freepost, Teddington, Middlesex TW I I I BR

Mr/Ms

Address

Postcode

MN, IN TOME1400W -to CieMVACAferaratr

0/7 ,r

goix001`'

Here's the Chrome -Chime-a perfect example of British scientificachievement brought right to your own front door. Now-you can beamong the first enthusiasts in the world to build your own electronicmusical door chime-a door chime with no moving parts. There are24 of the world's favourite and best known tunes pre-programmed ontothe microcomputer chip so that all you have to do is to set theChroma-Chi me's built-in selector switches to a code to index the"tune of the day" from the repertoire.

Since everything is done by precise mathematics, it cannot play thenotes out of tune.

The unit has comprehensive built-in controls so that you can not onlyselect the "tune of the day" but the volume, tempo and envelopedecay rate to change the sound according to taste.

Not only visitors to the front door will be amazed, if you like you canconnect an additional push button for a back door which playsa different tune!

This kit has been carefully prepared so that practically anyonecapable of neat soldering will have complete success in building it.The kit manual contains step-by-step constructional details togetherwith a fault finding guide, circuit description, installation detailsand operational instructions all well illustrated with numerous figuresand diagramsThe CHROMA-CHIME is exclusively designed by

CHROMATROMIC:River Way, Harlow, Essex.

Handsome purpose built ABS cabinet Easy to build and install Jses Texas Instruments TMS1000

microcomputer Absolutely all parts supplied including

I C socket Ready drilled and legended PCB included Comprehensive kit manual with full

:ircuit details No previous microcomputer experience

-ecessary All programming permanently retained

s on chip ROM Can be built in about 3 hours' suns off 2 PP3 type batteries Fully Guaranteed

ITMI=IM MIN NNW

o CHROMATRONICS, River Way, Harlow, Essex, U K.

£16-50Please send Ciroma -Chime Kits at leachincluding VAT and post and packing

PLEASE USE BLOCK CAPITALS

Name

Address

I enclose cheque/PO value £or debit my ACCESS/BARCLAYCARD account No.

Signature

IIII

IIIIII

N.B. The CHROMA-CHIME is also available, fullyassembled, price E 79.95 inc VAT and post and pecking.

EE 6/78mom um mom own Env

Everyday Electronics, June 1978 473

ELECTFE1111Iiii"EDUCATIONAL KITS OFEXCEPTIONAL QUALITY"

(AUDIO magazine)

Special offer to Readers ofEveryday Electronics only.

DENSHI KITS AT 20°/0This is a genuine offer of the ST -45 or SR -1A kits atthis bargain price for a limited period only.ST -45 Send £15.50 only, to include VAT pip,

educational manual. batteries and every-thing necessary to build 45 different actualworking projects and learn electronics atthe same time:You build: Radio receivers and transmitters.signal tracers and signal injectors, morse codeamplifiers and voice amplifiers, electronicbirds, guns, metronomes, and all types ofoscillators, metal detectors, radio guideddetectors, etc., etc., etc. ALL IN ONEFABULOUS KIT.

SR -1A Send £9 50 only, to include VAT, p&p,educational manual, batteries and every-thing necessary to build 16 different actualworking projects and learn electronicsat the same time:You build: Radio receivers and transmitters,amplifiers, morse code trainers, water levelwarning devices, signal tracers and injectors,etc., etc.

You can design and build your own circuits too withthese kits. No previous experience of electronics isrequired, but you certainly learn all about the subjectin practice with these tremendous kits, which arecompletely safe for anyone to use.All kits are guaranteed. Add-on sets (to increasethe number of projects) are available, plus sparesand accessories as required.We guarantee complete satisfaction with either ofthese kits.Special Offer applies to U.K. customers only.Callers at 20 Bride Lane will be very welcome (pleasebring this advertisement).Cheque/P.O./Barclaycard/Access No. (or 11p forillustrated literature) to Dept. EE

ELECTRONI-KIT20 BRIDE LANE, LUDGATE CIRCUS,

LONDON, EC4Y 8DX (01-353 6430)

SINCLAIR PRODUCTS'PDM35 digital multimeter L25 95.Mains adaptor £3 24. Deluxe paddedcarry case L3.25. 38kV probe £18.38.New DM235 digital meter P.O.A. Cam-bridge Scientific programmable calcu-lator £13.15. Prop library L4-55. Maineadaptor 13.20. Microvialon TV £200.CUT PRICE TELETEXTTeam Instruments XM11 Max module£120. Lebow 70211 ready to use, artrac-tively cased, complete unit. Plugs intoTV aerial socket. Full colour. Remotecontrol page select L355.

TV GAMES KITSSand s.a.e. for free data. Tank Battlechip AY -3-8710 plus economy kit £17 95.Stunt motor cycle chip AY -3-8760-1 pluseconomy kit £17.95. 10 game peddle2 chip AY -3-8600 plus economy kit£14.70. AY -3-8500 chip plus economykit £895. Modified shoot kit £4-95. Riflekit £4.95. Colour Generator kit £7.50.Joystick controls £190. 4-43MHz palcrystals 90o.ASSEMBLED TV GAMESAll attractively cased. 4 -game black andwhite model (tennis, football, squashand pelota) £11.95. 6 -game colour modelwith pistol attachment £2195. Tankbattle game £3995. Stunt motor cyclegame L39.95. Stabilized mains adaptorfor all games £3.10.MAINS TRANSFORMERS8-0-6V 100ma 79p, lie £2.35. 6 3V lia£1 89. 9-0-0V 75ma 79p, is £1.99, 2a£2-60. 12-0-12V 50ma 7917, 100ma 9017.la L2 49. 13V (a 950. 15-0-15V la L2 79.30-0-30V la L3.59.

JC12, JC29 AND JONI AMPLIFIERSA range of integrated circuit audioamplifiers supplied with free data andprinted circuits. JCI2 6 watts LI 60.JC2010 watts E.2 95. JC4020 watts L4 20.Send s.a.e. for free data on our range ofmatching power end pre -amp kits.

FERRANTI ZN414IC radio chip £1.05. Extra parts and pebfor radio £3.85. Case LI. Send s.a.e. forfree data.

PRINTED CIRCUIT MATERIALSPC Etching kits: Economy L1.70,Standard £3.82. 50 so ins pcb 400. 1 lbFeCI 41.05. Etch resist pens: Economy45p, Dalo 73p. Small drill bit 200.Etching dish 68p. Laminate cutter 75P

B ATTERY ELIMINATORB ARGAINSTV games power unit stabilized 7.7V100ma E3 10. 3 -way models withswitched output and 4 -way multi -lack:3/44/5V 100ma £2.92. 6/74/9V 300ma£3.30. Mime radio models same sizeas a PP9 battery with press stud con-nectors. 9v L2 85. (IV £2.85. 4(V £2 85.0V+9V 44 50. 6V+6V £4 50. 44V+44V£4 50. Cassette recorder mains unit74V 100ins with 5 pin din plug E285.Fully Mobilized model switched out-put 31)174'9V 400 me E840. Car con-vertors 12V de input. Output 9V 300ma£1.50. Output 74V 300ma £1.50.

B ATTERY ELIMINATOR KITSSend s.a.e. for free leaflet on range.Mama radio types with press studconnectors. 44V LI 80. 6V 41.80. 9V£180. 44+44V £2.50. 5+6V £2.50.9+9V £2.50. Cassette type 74V 10Ornawith din plug £1.80. Translator stake -lived II -way types for low hum3/411/74/9/12/15118V. 100ma L3 20 lAmo£6 40. Heavy duty 13 way types44/ 6 / 7/ 84/ 11 /13 / 14 / 17 /21 ,25 / 28 /34/42V. lAmp £4.65. 2Amp £7.25. Carconverter kit Input 12V de. Output617S/9V IA stebtlllzed. Stabilizedpower kite 3-18V 100ma £3.60. 3-30VIA £9-95 3-30V 241 £1495.

S-DECS AND T-DECS'S-DeC £3 39. T-DeC £4 44. u-DeCA£4 52. u-DeCB £667. 16 dil or 10106adaptors: with socket E214. NewS -de -kit £4 95.CONTINENTAL SPECIALITIESPRODUCTS'EXP300 El 21. EXP350 13 EXP600Cl 80. EXPOS° L3 N. EXP4B £2 49.PSI ES 114. PB100 £12 74. LM1 Si.LP1 £33 41. LP2 L1944.S I-PAK AUDIO MODULESSend sae for data. S450 tuner £23 51.ALSO £4 N. PAI00 RIC 71. SPUNE4 47. 8M140 LI IS. MKOO 11.311.74.Stereo 30 E21112.

COMPONENTSResistors 5% carbon E12 10 to Mt

tp. 1W 2p. Polyester capacitors250V ES .01 to 0118mf 75p. 0.1rnf 2p.15mf Sp. 22m1 Sp. .33, 47mf 8P.

Polystyrene capacitors E12 63V 150to 6800pf no. Ceramic capacitors 50VE12 not to t000pt 25p. ES 15000 104700001 Sip.

SWANLEY ELECTRONICSDEPT. EE, PO Box M, 32 Gold's' Rd., Swantey. Kent MRS ITQ

Mall order only. Please add 34Ip to the total cost of order for postage. Prices In-clude VAT. Overseas customers deduct 7% on items marked and 11A, on others.Official credit orders welcome.

r-Daram-Quality Range of Products

from The Doram Catalogue include:Single Semiconductors Hand ToolsWide range of singlediodes, zener diodes,rectifiers and generalpurpose transistors.

Integrated CircuitsQuality linear and digitalIC's, regulators etc.

Mains TransformersComprehensive top qualityselection of low voltagetransformers.

SwitchesA switch for mostapplications.

We stock a large range oftools for most electronicprojects.

BooksWe con supply a wide rangeof books from simpleprojects to detailed textbooks.

Wire & CableSmall or large quantitiesfrom a metre upwards.

To avoid disappointment EEI

send now for the currentDoram catalogue (edition 4) enclose 20p to cover post and pocking.

Name

Address

Derain Dorom Electronics Ltd PO Box TR8Wellington Road EstateWellington Bridge Leeds LS12 2UF

474 Everyday Electronics, June 1978

LOOK! Here's how youmaster electronics.....the practical way.

1 Build anoscilloscope.

As the first stage of y DUI training, youactually build your own Cathode rayoscilloscope' This is no toy, but a testinstrument that you will need not onlyfor the course's practical experiments, butalso later if you decide to develop yourknowledge and enter the profession. Itremains your property and represents avery large saving over buying a similarpiece of essential equipment.

T

This new style course will enable anyone tohave a real urderstanding of electronics by amodern, practical and visual method. Noprevious knowledge is required, no maths, andan absolute minimum of theory.

You learn the p-actical way in easy stepsmastering all the'essentials of your hobby or tofurther your career in electronics or as a self-employed electronics engineer.

All the training can be carried out in thecomfort of your own home and at your ownpace. A tutor is available to whom you canwrite, at any time, for advice or help duringyour work. A Certificate is given at the end ofevery course.

T

2 Read, draw andunderstandcircuit diagrams.

Ina sho-t time you wilt be able toread and draw circuit diagrams, under-stand the very fundamentals of television,radio, computors and countless otherelectronic devices and their servicingProcedures.

.7,=111.1=11.11611011111billdbWoo..4 )

-

ammsama 111111M11110&11

MR NMI MEI NMI N- M=1 MIMI EMI I=M r MEITo find out more about how to learn electronics in a new, exciting and absorbing way, just clip thecoupon for a free colour brochure and full details of enrolment.

:4111.0 -W2I "::' ?IP 4

2 1 1 5 6 'lc {co, ssi. rib

3 Carry out over40 experirnenison basic circuits.

We show you how to conductexperiments on a wide variety of differentcircuits and turn the information gainedinto a working knowledge of testing,servicing and maintaining all types ofelectronic equipment, radio, t.v etc.

A I students enrolling in our courses receivea free circuit board originating from acomputer and containing many differentcomponents that can be used in experimentsand provide an excellent example of currentel actron ic practice.

British National Radio & Electronic SchoolP.O. Box 156, Jersey, Channel Islands.

NAMEADDRESS

EE 86 ;1.1 ,1[

MEM OMNI OMB MN MINN M=11 NMI NMI NMI IIMM NM NM MOEveryday Electronics, June 1978 47.-)

SEMICONDUCTORS COMPONENTSCERAMIC PAK

Containing of first qualityminiature ceramic capacitors.16160-24-3 of each ye/sm.-220,

27pf, 33pf, 39pf, 470, 68pf,1320. 60p'

16161-24-3 of each value:-100Pf.120pf, 150pf, 180pf, 2200,270pf, 330pf, 390pf. 600.

16162-24-3 of each value: -470p(,560pf, 680pf, 820pf, 1000pf.15000pf, 2200pf. 3300pf.609.

16163-21-3 of each value:-4700pf , 6800 pf, 01 uf, 0 I 5uf022uf, 033uf. '0470. 60p

ELECTROLYTICPAKS

A f pales each contain-ing III first quality. mixed valuemini a lectrolytics.1620I -values

from 47mFD-lOrriFD 60p16202 -values

from 10mFD-10OrnFID 60916203 -values

from 10OrnED-680mED 60p.

CARBONRESISTOR PAKS

These poke contain a aaaaa ofCarbon Resistors assorted intothe following groups.16213-40 mixed 4w

100ohms-/320ohms 60p.16214-60 mixed ew

1Kohms-8 2Kohms 60p16215-60 mixed ew

I0Kohms-83Kohms 60916216-60 mixed ew

100Kohms-820Kohms 60p16217-40 mixed ew

100ohms-820ohms 609*16218-40 mixed 4w

IKohms-8 2Kohivis 60p16219-40 mixed eve

10Kohms--82Kohins 609.16220-40 mixed ew

100Kohms-820Kohrns 60916230-60 mixed ew

IMeg-10 Meg ohms 60p16231-40 mixed ew

I Meg -I0 Meg ohms 609

COMPONENTPAKS

16164-200 Resistor mixed valueapprox. (Count by weight)

60p16165-150 Capacitors mixed value

approx. (Count by weight)60p'

16166-50 Precision resistors. Mixedvalues 609

16167-4w resistors mixed values 8060p

16168-5 pieces assorted ferrite rods60p

16169-2 Tuning gangs MW.LWVHF 60p

16170-I Pack wire 50assorted colours singlestrand 609

16171-10 Reed switches 60p16172-3 Micro switches 60p16173-15 Assorted pots60p16174-5 Metal jack sockets 3 x

3 5mm 2 x standardswitch types 60p

16175-30 Paper condensers -mixed values 60p

16176-20 Electrolytics trans. types609.

16177-I Pack assorted hardware-Nuts/bolts, gromets etc.

60916178-S Mains slide switches

assorted 60p16179-20 Assorted tag strips and

panels 60p16180-15 Assorted control knobs

60p16181-3 Rotary wave change

switches 60p16182-2 Relays 6-24v operating

60p16183-I Pak. copper laminate

approx. 200 sq. inches 60p16184-15 Assorted fuses 10OrnA-

5amp 60916185-50 M PVC sleeving

assorted size and colours609

16188-60 ew resistors mixed valuesUse

16186-25 P assorted typesand value 60p

16187-30 M ded wireassorted 60p

Type PriceACI26 LO 111ACI27 LO 18AC128 LO ISACI28K 1026AC132 CO 20AC134 LO 20AC137 LO 20ACI41 L022ACIIIK LO 30AC142 LO 20AC176 LO 18AC I 76K CO 16AC178 LO 23AC179 LO 15ACI80 LO 20ACIBOK LO 76ACI81 CO 20ACI81K LO 18ACI87 LO 18AC 187K LO 10AC188 LOAC INK LO 20A0I40 LO 60ADI42 CO 115A0143 LO 75ADI49 LO 60A0161 LO 42ADI62 LO 42AD1611161MP

L0.35AF114 LO 11AFII5 L021AFII6 1021AFII7 LO 21AFII8 LO 40AF124 LO 30AFI25 LO 30AF126 LO 30AF127 LO 32AF 139 LO 35AFI80 LO 40AFI81 LO 60AFIB6 CO 511AF239 LO SOAL102 LO 38AL103 LI 10AU104 LI 18AU110 II 00AUII3 LI 00BC1074 LO 08BC 107B LO 08BC107C LO 08BC1011A LO 08BC1086 LO 08BC108C LO 08BCI0913 LO 08

TRANSISTORSBRAND NEW - FULLY GUARANTEED

Type PriceBC109C LO 08BCI47 LO 08BC148 LO 08BC149 LO OSBCI57 LO 10BC'S. LO 10BCIS9 LO 10BCI67 LO 12BC168 L0.12BC169 'CO 12BC(69C LO 12BCI70 'CO 10BCI71 'CO 10BC172 *L0-10BC173 LO 12BC177 LO 16BC178 LO 16BCI79 (0 16BC I80 LO 23BC181 'CO 23BCI82L 'CO 10BCI83 LO 10BCI83L LO 10BC184 LO 10BCIB4L LO 10BC207 10 11BC208 LO II

BC209 'CO 12BC212 LO IIBC2I2L 'CO IIBC2I3 LO 11BC2I3L LO IIBC2I4 LO 12BC2I4L LO 12BC237 'CO 16BC238 LC1 16BC2.51 LO 15BC23IA 'CO 16BC301 LO 2/1BC302 LO 18BC303 LO 2.8BC304 LO 38BC327 'CO 16BC328 LO ISBC337 ./03 ISBC338 'CO 15BC440 LO 308C44I LO 30BC460 LO 38BC461 LO 38BC477 CO 10BC478 LO 20BC479 LO 20BC547 'CO 12BC548 LO 12BC549 1012

Type PriceBC550 LO.14BC556 'CO 14BC557 .1013BC556 L0.12BC559 'Co -1480115 LO SOBDII6 LO 80BDI21 LO 6580124 LO 7080131 LO 3880132 LO 40130131r

132MP LO 85130133 LO 4080135 LO 38130136 LO 3580(37 LO 3580I38 LO 40BD139 CO 3680140 LO 36130139

140MP LO 80130155 LO 80BDI75 CO 6080176 CO 6080177 LO 6880178 10 6480179 LO 7580201

202MP LI 7080203 LO 8080204 LO 8060203

204MP LI 70BOY20 LO 80BDX77 /0.908E457 LO 37BE4586E4596E5948E596BFR39URI°BFR79BFR80BFX29BFX30BFX84BEMISBFX86BFXB7BFX88BF X90BFY50BFY5 I

LO 3710 38

.1.0 30'CO 28

CO 24. L0 2S*CO 28.L0 28

LO 22/030LO 14LO 24LO 23LO 21LO 22

. 16 55LO 16CO 16

Type PriceBFY52 10 16BIPI9 LO 38BIP20 LO 38BIPI9

20MP LO 80BRY39 LO 45BUIOS L1 40BUI05 02 Cl 95BU204 LI 70131.)205 LI 70BU208 12 23BU208 02 L2 93E I 222 LO 38MIE2955 LO 98M1E3055 LO 60MJE3440 LO 52MP8 I 13 LO 52MPE102 LO 35MPFI04 LO 38MPF1OS LO 38MPSA05 10 30MPSA06 LO 30MPSA55 'CO 28MPSA56 'CO 180C22 LI 500C23 LI 500C24 LI 350C25 LI 000C26 ,1 000C213 LO 800C29 LO 950C35 LO 900C36 LO 900070 LO 240071 LO ISTICK LO 29TIC45 LO 35TIP29A LO 40TIP29B LO 52TIP29C 10 SOTIP30A CO SOTIP3013 LO 60TIP30C LO 60TIP3I A LO 43TIP3IB /0 47TIP3 IC LO 49TIP32A LO 49TIP32B LO SITIP32C CO 53TIP4 I A 10 49T1P4 1 B LO SITIP4 IC LO 53TIP42A LO 53TIP42B LO 55TIP42C L0.57TIP2955 113 63

Type PriceT1P3055 LO' 5011543 LO 24T1590 LO 12UT46 'CO 22ZTX107 LO 10ZTX1013 LO 10ZTX109 'CO .10ZTX300 'CO 12ZTX500 ./13 142NI6132N17112N113892N 18902NI8932N2I472N21482N2I602N21922N2193

LO 20LO 20LO 45LO 45LO 30LO 75LO 70LI 00LO 38LO 38

2N2194 LO 382N2217 CO 222N22)8 LO 212N2218A LO 202N2219 LO 202N2219A 10 242N2904 LO IS2N29044 CO 212N2905 LO 182N2905A LO 202N2906 LO 162N2906A LO 192N2907 10 102N2907A LO 222N296G LO 092N2926Y10 0112N2926010 082N2926R10 062N2926BLO 082N3053 LI) 162N30542N30552N34142N34)52N34162N34172N36142N36152N36162N36462N37022N37032N37042N37052N37062N37072N3708

CO 40'CO 16' CO 16'CO 29' CO 19LI 0011 OSCI 05

' CO 09"(0 08'CO OS'CO 07'CO 07'CO OS"LO OS' CO 07

Type Price2N37084A

LO 072N3709 LO 072N3710 'CO 072N3711 LO,072N3819 LO 202N3820 LO 352N3821 LO 602N3823 LO 602N4058 LO 122N4059 LO 142N4060 LO 142N4061 LO 122N4062 10122N4284 LO 182N4285 'CO 162N4286 LO 182N4287 'CO 182N4288 .L0 182N4289 'CO 182N4290 LO 182N4291 LO 182N4292 LO 182N4293 'CO 182N4921 'Co SS2N4923 'CO 652N5135 LO 102N5136 LO 102N5I38 LO 102N5194 CO 562N5245 LO402N5294 LO 342N52962N54572N54582N54592N55512N60272N61212N612240311403134031640317403264032740346403474034840360403614036240406404074040840409

LO )2LO )2LO 38

'CO 36CO 39LO 70LO 70LO 38LO 95LO 95LO 40LO 40LO 45LO 45LO 65CO 80LO 36LO 36CO 18LO 45LO 35LO 51LO 75

Type Price Type7400 10 14 74097401 10 14 74107402 LO IS 74117403 LO IS 74127404 CO IS 74137405 LO IS 74147406 LO 30 74167407 LO 30 74177408 LO IS 7440

74 SERIES TTL IC'SFULL SPECIFICATI

Price

LO ISCO 14LO 13LO 23LO 17CO 5$10 211

LO 2111

LO IS

81-PAK STILL LOON GUARANTEED

Type744174427445744674477448747574807481

Price

CO 64CO -64

LO 90LO 90CO 78LOLO 44LO -SO

10 95

WEST IN PRICE.

Type748274837484748574867489749074917492

PriceLO 85LOLO 9SLI 00LO 30L2 50LO 42CO 75LO 45

Type74937494749574967410074110741187411974121

Price Type PriceLO 40 74122 CO SOLO 811 74123 LO 70[0-70 74141 CO 60/0-110 74154 Cl 20/1110 74180 LI 00LO SO 74181 Cl 00LO 90 74190 LI 40LI 85 74198 LI 85CO 30 74199 LI ES

CMOS IC'SType Price Type Price Type Price Type Price Type Price Type PriceCD4000 LO IS CD4012 L0.20 C04022 LO 90 CD4031 L2 10 CD4046 LI 30 CD4071 LO 23C04001 LO IS C04013 LO .52 C04023 LO 20 CD4035 LI 301 CD4047 LI 10 CD4072 CO 23CD4002 LO 18 CD4015 LO 981 C04024 LO BO CD4037 LO 93 CD4049 LO 55 CD4081 CO 20CD4006 CO 91I C04016 LO SO CD4025 LO 10 CD4040 10 93 CD4050 LO SS CD4082 LO 13CD4007 LO IS CD4017 LO 98 CD4026 LI 70 C04041 LO 111 CD4054 LI 10 CD4510 LI 30CD4008 CO 98 CD4018 LI 00 CD4027 L0.60 CD4042 CO 82 CD4055 LI 40 CD4511 LI 60CD4009 LO SS CD4019 LO 531 CD4028 LO 98 C04043 LO 98 CD4056 LI 35 CD45I 6 LI 40CD4010 LO S8 CD4020 Cl 10 CD4029 LI IS CD4044 LO 94 CD4069 LO 40 CD4518 LI 23CD4011 L0.20 C04021 /CI 98'! CD4030 LO 55 CD4045 LI 40' CD4070 CO' 40 CD4520 LI 23

LINEAR IC'SType PriceA7I0C LO 40

72710. LO 30uA711C CO 3272711* L0.32uA723C 16 4572723 CO 45uA74IC LO 247274I LO 2474IP LO 20u4747C CO 7072747* LO 79uA748. CO 3572748 10 35748P LO 35

SENDYOURORDERSTO

Type PriceSN76013N

LI 7SSN76023N

LI 75SN76110*

LI SOSN76115.

LI 90SN76660.

LO 75SL414A LI 95TAASOB LO 35TAA62IA

12 00

Type PriceTAA66IA

LI 65TAD100 LI 30TBA540Q

12 20TBA64I son 23TBA800. LO SOTBA810S

LI OSTBA820. LO SOTBA920Q

LI 40TCA270S

12 29

MIDGET WAFERSWITCHES

1965-1 pole 12 way 48p1966-2 pole 6 way up'1967-3 pole 4 way 48p1968-4 pole 3 way 4119

IC PAKSMenu( "Fall -outs"which include functional Units.Thsis are classed as 'out -of -spec'from the maker's very rigidspecifications, but are ideal forlearning about I.C's and ex-perimental work.16224-100 Gates assorted

7400-01-04-10-50-60 etc.LI 20

16226-30 1451 Assorted types7441-47-90-154 etc. LI 10

16227-30 Assorted Linear Types709-741-747-748-710-588 etc

LI 5016228-8 Assorted types SL403

76013. 76003 etc. LI 0016229-S I.C's 76110 Egv. to

MC1310P-M4767 LI SO*

MAMMOTH I.C.PAK

16223-Approx. 200 piecesAssorted fall -out integrateocircuits, including: Logic,74 series, Linear, Audio, andD.T.L. Mandy coded de-vices, but some unmarked -you to identify LI 20

UNTESTEDSEMICONDUCTOR

PAKS16130-100 Germ gold bonded

0A47 diodes 60916131-150 Germ.

100mA 0A70181 diode609

16132-100 Silicon diodes 200mA0A200 609

16133-150 Silicon fast switch diode75mA IN41413 609

16134-50 Silicon rectifiers top hat750mA 609

16135-20 Silicon rectifiers studtype 3Amp 60p

16136 -SO 400mW yellers D07 case60p

16137-30 NPN transistors BCI07,8plastic 60p

16138-30 PNP transistors BC177178 plastic 60p*

16139-25 NPN 1039 2N697i2N17Il silicon 60p

16140-2.5 PNP TO39 2N2905silicon 609

16141-30 NPN TO18 2N706silicon, switching 60p

16142-25 NPN BEY50 51 60916143-30 NPN plastic 2N3906

silicon 60p16144-30 PNP plastic 2N3905

silicon 60p16145-30 Germ. 0071 PNP 60p16146-15 plastic power 2N3055

NPN TO220 case LI 1016147-10 103 metal 2N3055 NPN

Cl -2016148-20 Unijunction transistors

T1S43 60p16149-10 lamp SCR 1039 LI 2016150-8 3ainci SCR T066 case

LI 20

ORDERING Do not forget to stateorder number and your name andaddress.V.A.T. Add 124% to pricesmarked , 8% to those unmarked.Items marked are zero rated.P & P. 35p unless otherwise shown

Dept. E.E. 6, P.O., Box 6, Ware, HertsSHOP 18 BALDOCK STREET, WARE, HERTS

AT: OPEN 9 to 5.30 Mon./Sat.


Type PriceCA3011* LI OSCA30146 LI 70CA2018. CO 75CA3020 LI 70CA30213 LI 02CA3035 LI 70CA3036* LI 35CA3042 LI '30CA3043 LI $5CA3046 CO 80CA3052. LI 60CA3034. LI 35CA3075' LI .SOCA3081° LI SOCA3089. LI 10CA3090. L4 23CA3123* LI 90LM301. 10.39LM304 41.60LM308. LI 40LM309K LI SOLM320-5v LI SOLM320-12v

LI - 50

Type PriceLM320-15v

LI SOLM320-24v

LI 50LM380-14P

LO 85LM381. LI S5LM3900N

LO 65MC742P LI SOMCI303L

LI 48MCI 3041.

LI 90MC1310P

LO 95MCI312PQ

11 90MCI330P

LI 10MC1350. LI 10MCI3SIP'

LI 20MC1352P

LI 40

Type Price

MC 1456GLI 40

MCI466L L4 50MCI469R L1.95MCI496G

CO 98NE536. 13 SONE5I5A 13.50NE540. LI .50NE550. LO 95NE550D NLANE5S5 LO 31NE556 LO 82NE56I (3 95NE56211. /3 OSNE565A LI 75NE566. LI 50NE567. II 110

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ALL THE PARTS YOUNEED TO BUILD THESTUNT CYCLE PROJECTTHE MOST COMPULSIVE TV GAMEEVER MADE

atuni sounds come directly from the TV * Realistic crash effects.1 penalty points. * Four competitive games with amateur and professional mods.

* On -screen scoring * Up to 30 buses can be jumped. * Throttle has the 'feel'of a motorbike: too much and you will skid and crash, too little and you will not getover the buses or obstacles.

141 o

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All prices include VAT. For orders under £10 add 20p pitp. Cheques and posralorders to be made payable to TELEPLAY; send your order (no stamp neecliit.-Io:Tistep ay. Freepost. Barnet, ENS MR, or telephone your order quot Ing your Barclay-card or Access number.

SANCLOYEA110 SHOP OPEN 10 a.m.-7 p.m.. Monday to SaturdayCLOSE TO NEW BARNET BR STATION-MOORGATE LINE. Trade enquiries welcome

41 STATION ROAD,NEW 3ARNET, HERTS.ENS IOW r' 0-.440 7033 01-441 2922

TECHNICAL TRAININGIN ELECTRONICS AND

TELECOMMUNICATIONSICS can provide the technical knowledge that is so essential to your success:knowledge that will enable you to take advantage of the many opportunitiesopen to you. Study in your own home. in your own time and at your ownpace and if you are studying for an examination ICS guarantee coachinguntil you are successful.

City and Guilds Certificates:Telecommunications TechniciansRadio, TV, Electronics TechniciansTechnical CommunicationsRadio Servicing TheoryRadio AmateursElectrical Installation WorkMPT Radio Communications Certificate

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1 Subject of InterestNameAddress 111

Teli Age:..

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THE NEWEUROBREADBOARD

Logically laid out to accept both 0.3" and 0.6" pitch DIL packagesas well as Capacitors, Resistors, LED's, Transistors and componentswith leads up to .85mm dia.

500 individual connections in the central breadboarding area,spaced to accept all sizes of DIL package without running out ofconnection points.

4 Integral Power Bus Strips around all edges for minimum inter-connection lengths.

Double -stied, nickel silver contacts for long life (10K insertions)and low contact resistance (<10m.ohms)

Easily removable, non -slip rubber backing allows damaged contactsto be rapidly replaced.

What other breadboarding system has as many individual contacts,offers all these features and only costs £5.80 inclusive of VAT andP.P. - NONE.

At £5.80 each The EuroBreadBoard is unique value for money.At £11.80 for 2 The EuroBreadBoard is an indispensable design aid.

Snip out and PostDavid G Sales, r'o 74 Crayford Hi h S[.. Craylord,p..

David George Salesr/o 74 Crayford High Street,Crayford, Kent, DA1 4EF.

Please send me 1 EuroBreadBoard @ £5.80 0 Pleaseor 2 EuroBreadBoards@ £11.00 0 Tick

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EDITORF. E. BENNETT

ASSISTANT EDITORB. W. TERRELL B.Sc.

PRODUCTION EDITORD. BARRINGTON

TECHNICAL SUB -EDITORT. J. JOHNSON G8MGS

ART EDITORR. PALMER

TECHNICAL ILLUSTRATORSP. A. LOATESD. J. GOODING

EDITORIAL OFFICESKings Reach Tower,Stamford Street,London SE1 9LSPhone: 01-261 6873

ADVERTISEMENT MANAGERV. PIERIPhone: 01-261 6727

REPRESENTATIVEP. J. MEWPhone: 01-261 6676

CLASSIFIED MANAGERC. P. BROWNPhone: 01-261 5762

MAKE-UP AND COPYDEPARTMENT

Phone 01-261 6035

ADVERTISEMENT OFFICESKings Reach TowerStamford Street,London SE1 9LS

Projects... Theory...

and Popular Features ...

Our Tele-Bell should be very popular.Telephone subscribers will find thisdevice a boon. With the summerahead, and all those long hours likelyto be spent in the garden, now is aparticularly good time to build thisunit. One can then concentrate onweeding the flower beds or hoeing therows of vegetables, or just indulge ina quiet siesta on the patio or lawnknowing that the outside extensionbell will be heard when the telephonerings.

The remote or extension bell can ofcourse be installed anywhere withinthe house, in the garage or gardenshed, to meet the special requirementsof a household.

And this is not all. The remoteindicator may be a lamp, rather thana bell or buzzer. This would be moreappropriate if installed, for example,in the TV lounge.

Being essentially a sound -operatedrelay, the Tele-Bell has other usefulapplications; such as a Baby Alarm,or a remote indicator of a caller atthe front door.

In the latter or in the phone applica-tion, the aged, handicapped, or hard ofhearing will find the facilities offeredby the Tele-Bell of genuine practicalassistance.

We can leave it to our readersto make good use of this project,

whether in their own home or in thatof a friend or neighbour.

A 100 watts of audio! My, the mindboggles. Yet this is nowadays theaccepted norm in the pop world.Powers of 200 watts and even higherare not unusual either.

It seems that stimulus via the ear isbut a secondary consideration. Popmusic relies chiefly upon the sensualeffect of low frequency sound wavesimpinging upon the diaphragm andabdomen. Thus the incessant demandfor watts and more watts.

To help satisfy (albeit in part only)this demand for 100's of watts weoffer this month the EE Power Slave.The cool 100 watts of audio deliveredby this excellent portable equipmentshould help meet the requirements ofpop groups, and will certainlyadequately cover the needs for publicaddress systems in medium or largesize halls.

Our July issue will be published on Friday, June 16. See page 503 for details.

Readers' EnquiriesWe cannot undertake to answer readers' letters requesting modifications,

designs or information on commercial equipment or subjects not publishedby us. All letters requiring a personal reply should be accompanied by astamped self-addressed envelope.

Telephone enquiries should be limited to those requiring only a brief reply.We cannot undertake to engage in discussions on the telephone, technicalor otherwise.

Component SuppliesReaders should note that we do lot supply electronic components for

building the projects featured in EVERYDAY ELECTRONICS, but theserequirements can be met by our advertisers.


ELECTRONICSVOL. 7 NO. 10 JUNE 1978

CONSTRUCTIONAL PROJECTS

TELE-BELL A sound -operated monitoring device for the home by F. G. Rayer 480

IN -SITU TRANSISTOR TESTER Carry out in -circuit spot-checks with this unit by R. A. Penfold 486

EE 100W POWER SLAVE Plug-in to "big sound" with this 100W power amplifier by E. M. Lyndsell 504

VISUAL CONTINUITY TESTER Narrows down the ohmic value of circuit under test by A. Sproxton 516

GENERAL FEATURES

EDITORIAL 478

CROSSWORD No. 4 by D. P. Newton 484

SHOP TALK New products and component buying for constructional projects by Dave Barrington 485

BRIGHT IDEAS Reader's hints and tips 490

FOR YOUR ENTERTAINMENT Video at the summit, compatibility check by Adrian Hope 491

CLUB CORNER News from amateur organisations 491

BRAIN ON A GRAIN -2 The impact microprocessors are having on everyday living by S. McClelland 492

JACK PLUG AND FAMILY Cartoon by Doug Baker 495

TEACH -IN 78 Part 9. Radio, Modulation, Receivers by George Hylton 496

READERS' LETTERS Your news and views 513

EVERYDAY NEWS What's happening in the world of electronics 514

PROFESSOR ERNEST EVERSURE The Extraordinary Experiments of. by Anthony J. Bassett 520

Back issues of EVERYDAY ELECTRONICS (June 1977 onwards --October, November, December 1977 and January 1978 NOT available)are available worldwide at a cost of 60p per copy inclusive of postageand packing. Orders and remittance should be sent to: Post SalesDepartment, IPC Magazines Ltd., Lavington House, 25 LavingtonStreet, London SE1 OPF.

Binders for Volumes 1 to 7 (state which) are available from the aboveaddress for £2 85 inclusive of postage and packing.c IPC Magazines Limited 1978. Copyright in all drawings, photographs and articlespublished in EVERYDAY ELECTRONICS is fully protected, and reproductions orimitations in whole or in part are expressly forbidden.

All reasonable precautions are taken to ensure that the advice and data given toreaders are reliable. We cannot however guarantee it, and we cannot accept legal re-sponsibility for it. Prices quoted are those current as we go -.o press.


THIS device will control a signallamp, bell or buzzer either

locking on or giving intermittentwarning. It is sound triggered andso can be used to alert one to theringing of a telephone bell, door-bell or some other sound sourcefor positions remote from thesound source.

As a sound triggered telephonebell warning (expected to be itsprimary application), it can controla signal lamp or bell located in akitchen or television room, or else-where in circumstances where thetelephone may not be readilyheard. For a doorbell extension, itcan operate in a similar way,though an indicator lamp will bechosen when ringing of a doorbellis to be signalled to a deaf person.It could also serve as a baby -cryalarm.

Although the unit is shown asmains powered, it can easily beadapted for battery operation bysimply omitting the power supplysection. This modification howeverremoves the intermittent facility.

CIRCUIT DESCRIPTIONThe complete circuit diagram of

the Tele-Bell is shown in Fig. 1.An inexpensive crystal microphoneinsert is used as the sound pick-updevice. The signal originating in

ELE-BELLBY F. G. Rayer

the microphone is passed to anaudio amplifier composed of ICIand associated components. Thisi.c. is the well known 741 differen-tial operational amplifier tailoredfor audio signals and provides again of 100.

The output of ICI is fed via a d.c.blocking capacitor to the base ofTR1. The collector current in TR1is negligible until an audio signalis present in the system resultingin the potential on the collectorbeing close to ground.

NEGATIVE DRIVEWhen a signal is present at the

output of IC1, it passes through C2and is then rectified by diode DIto provide a negative drive biasfor TRI base. Collector currentflows and therefore causes a volt-age drop across VR1. In otherwords the collector potential rises;the amount of rise is controlled bythe effective value of VRI and canbe adjusted to suit the sensitivityrequired.

The collector potential is directlycoupled to the gate of CSR1 andwhen sufficiently high causes CSR1to switch on. This places 12 voltsd.c. at the output (extension)sockets SKI and SK2, which is in-dicated by LP1 illuminating.

A low costremote mon

Ideal for the housewife-in

itor.

the kitchen. in the workshopThe handyman-or greenhouse.Also an invaluable

aid for the

aged or disabled.

This lamp will be found particu-larly useful when setting the sensi-tivity when the extension bell orbuzzer is not connected. Diode D2is included to suppress back e.m.f.generated when the extension bellor buzzer is operated.

To maintain current throughCSR1 when the alarm tremblercontacts are open, should the lampfail, resistor R7 is included.

MODES OF OPERATIONMode of operation is controlled

by the 3 -way switch Si. If S1 isat Loci< CSR1 receives current rec-tified by D3 and smoothed by C4.The thyristor thus remains in theavalanche or conducting state,even if the sound operating thedevice is only momentary. Turningthis switch to MUTE interrupts cur-rent so that the thyristor returns


to the non -conducting condition.Should S1 be at NON LOCK then thethyristor receives current directlyfrom the transformer, so remainsin conduction only while sound ispresent (since it turns off on everynegative excursion of the a.c.secondary voltage). Therefore anindicator lamp or extension bellwill only operate. while the phonebell is actually ringing.

Switch section Slb removessupply voltage from ICI and TR1,so that there is a slight delay whenswitching to LOCK ON or NON LOCKpositions. This avoids having toswitch off with the mains switchS2, wait a short interval, thenswitch on again.

If the unit is always to be usedwith an indicator lamp only, D2and R7 can be omitted.

CIRCUIT ACTIONMains voltage enters the unit

via S2 and FS1 and appears acrossthe primary of T1. This is steppeddown to 9 volt a.c. which appearsacross the secondary of Tl. Halfwave rectification is achieved byD3 and smoothing accomplished byreservoir capacitor C4.

SK1

(LMCI

R2100k12

L-JCITicp,

HOW IT WORKS

Brrr

Brrl

8,

- le

SWITCH

Sound from a remote source such as a telephone, is picked up by themicrophone and amplified to a suitable level by the amplifier. The amplifierhas a sensitivity control to allow different sound levels to operate theunit co-rectly. The output from the amplifier is rectified to produce a"voltage spike" which is used to operate the switch.

The switch itself is of the electronic variety and is arranged to havea "latching" action. This means that once the switch is operated, it re-mains cperated. The output from the switch is used to control an externalwarning device such as a bell or buzzer. The warning device can beplaced at any remote point, thereby giving a warning that the telephonehas been ringing.

Supply voltages for IC1 and TR1are derived from the 12 volt levelby R6 and C3 and these com-ponents introduce a short delay inoperation of these stages to avoidtriggering the unit at switch on.

A d.c. level of 12 volts is avail-able for the remainder of the

Fig. 1. Complete circuit diagram for the Tele-Bell.

F;FN

R62.2k11

rt

"um 22 00p F

R9 15011

C3

IN4001D2 C)

0 Sib

circuitry. Capacitors C5 and C6 areincluded to help suppress trigger-ing by noise or transients on themains supply.

The prototype unit employed athyristor rated at 3 amps when a1 amp type would be sufficientunder normal operating conditions

ICALLI

CSR1*CSR3/05

D3 IN4001

1LOCK ON51aoisiltOMUTE

I NON LOCK

LP16V60mA

REMOTE]BELL

R8loon

*SEE TEXT

CSK2(12V)

SK3(0V)

qd

qd

Ov

ON/OFF

WE IL

Everyday Electronics, June 1978

240V A.C.MAINS

481

with the specified transformer.However, this was chosen so as notto require any heatsink.

If a thyristor rated at 1 amp isused, it will probably not be in thesame case style as that shown inFig. 3 and connection details willneed to be investigated. It maythen be necessary for this deviceto be fitted with a heatsink.

STARTHERE FOR

CONSTRUCTION

COMPONENT ASSEMBLYAll of the components are

mounted on the rear face of thefront panel, and most of the com-ponents are assembled on a pieceof 0.15 inch matrix perforatedboard size 28 x 24 holes as shownin Fig. 3 and 4. The board issecured to the front panel bymeans of a metal bracket bolted tothe board and sandwiched betweenthe front panel and VR1.

Begin construction by cuttingthe board to size and drilling tosuit CSR1, SK1 and the bracketfixing bolts and then assemble thecomponents as shown in Fig. 3. Inmost places the wire ends of theresistors and capacitors will belong enough to reach the connect-ing points. If not, some tinnedcopper wire will be required. Whenassembling IC1, note that pin 8 isclosest to the tag on the body, seeFig. 3.

The next stage is to prepare thefront panel to accept the panelmounted components. With thesesecured in position, using counter-sunk bolts for the transformer andlampholder fixings, the board canbe secured in place on its mountingbracket and then wired up to therest of the components accordingto Figs.2 and 4.

CASEThe prototype unit was housed

in a home-made wooden case, anddimensions of this are given inFig. 5 for those wishing to make asimilar housing. Each side is re-bated along its sloping edge to

accommodate the front panel. Theupper and lower edges of the frontpanel are chamfered as necessaryto obtain a good fit, and is thensecured with two small woodscrews.

EXTENSION CIRCUITCurrent drawn by IC1, TR1 and

LP1 should be no more than about70 milliamps therefore with thespecified transformer a bell orbuzzer with a current rating of upto 1 amp can be used, or a 12 voltlamp of up to 12 watts rating. A3 watt lamp should be adequatefor most applications.

Several lamps can be fitted inparallel and located in differentrooms for instance, but observethe maximum wattage rating. Iftwo bulbs are used, these musteach be rated at 6 watts or less,or if 4 lamps are required thesemust be rated at 3 watts or less.Remember that the total wattageof a parallel lamp system is ob-

coDANck._do44- ESTIMATED COSTOF COMPONENTS

£6'00excluding

case

tained by adding the individualwattage ratings of the lamps.

The extension cable can be ofany length, except that very longthin leads will reduce the voltageto the bell or buzzer or lamp itheavy currents are flowing.

A bell or buzzer can be any-where in the room, but a lampshould be placed where it will bereadily seen (for example, in asmall fitting on top of a televisionset if used in the lounge).

COMPONENTSResistors

R1 100kn R4 100kf2 R7 1 kilR2 100ki2 R5 470kf2 R8 100f) 1WR3 114-2 R6 2.2k11 R9 1500All PN carbon ±5% except where otherwise stated

PotentiometerVR1 1ki2 lin. carbon

CapacitorsC1 10µF 10V elect. C4 2200µF 16V elect.C2 10nF plastic or ceramic C5 10nF 400V a.c.C3 1000µF 16V elect. C6 5nF 400V a.c.

SemiconductorsD1 0A47 or similar germanium diodeD2 1N4001 or similar 1 A silicon diodeD3 1N4001 or similar 1 A silicon diodeTR1 AC128 germanium pnpCSR1 CRS3/05 or similar 3A thyristor (see text)IC1 741 differential operational amplifier TO -5 style case

MiscellaneousLP1L P2S1S2T1

6V 60mA SK1mains panel neon SK2, 32 -pole 3 -way rotary PL1on/off mains toggle single pole MIC1mains primary/9 volt 1 amp FS1

secondaryPerforated s.r.b.p. 0.15 inch matrix size 28 x 24 holes; 20mm panel mount-ing fuseholder; holder and lens for LP1; screened lead; mains cable;plastic knobs (2 off); solder tags (2 off); mains cable retaining clip; grom-met to suit mains cable; 6BA fixings; materials for case; aluminium forcomponent board mounting bracket.

See

page 485

3.5mm jack socket4mm sockets (2 off)3.5mm jack plugcrystal microphone insert500mA 20mm fuse


METAL BRACKET

Fig. 2. Layout of components on the front panel and inter -wiring.

FRONT PANELTAPERED ALONGTOP IT BOTTOMEDGES

8

OVERALL DIMENSIONS OF CASE

HEIGHT 140mmWIDTH 165mmDEPTH 127mm

Fig. 5. Suggested arrangement and main dimensions for thecase.

POSITION OFCOMPONENTBOARD

MIC1

9

CSR1

a

e=VEROP1NSI

741

UNDERSIDE VIEWS

0000004000000000000004000000000

0o 0- elb

TR I

RSBOC )R2

C2 ,E=Fis

o R7RVI1/4.4Thr) _011,R3

O0000000000000000 RID 00000 SKI,

R9.com* ici

ci

Fig. 3. Component layout for the topside of the circuit boardand connections for TR1 IC1 and CSR1.

©

0 D 0 0 0 00

Fig. 4. Underside wiring of the component board. The MICjack socket SK1 was mounted on the component board inthe prototype, but should be mounted on the case backpanel and wires taken from the board to S1(1 solder tags.


Top view of the componentboard and rear of the frontpanel. Note that in the frontpanel wiring Fig. 2. theconnections to T1 areshown either side of themains transformer for easeof wiring.

ADJUSTMENT

It was found that the maximumsensitivity which is available isvirtually unusable in the LOCK posi-tion. It is practicable to set VR1for greater sensitivity when usingthe NON Loci( position. With theswitch at LOCK turn VR1 clockwise

until the lamp LP1 is lit whensnapping the fingers a foot or twofrom the microphone. Later, VR1should be set to suit conditions.

Too great a sensitivity willcause the circuit to be triggered bylow level sounds. Unwanted opera-tion of the circuit in this way isvery probable if the microphone is

a long way from the telephone (ordoor bell), with sensitivity set high.But with sensitivity reduced byVR1, and the microphone reason-ably near the phone or other soundsource, unwanted triggering of thecircuit will be avoided.

Once the unit has been triggeredin the Loci( position, it will benecessary to turn switch Si toMUTE to cancel the extension bellor lamp.

BATTERY OPERATIONFor a battery operated Tele-Bell

omit S2, D3, C5, C6, R9 and thetransformer. As the power is nowd.c. only, no NON LOCK position isavailable. The thyristor can be re-stored to its non -conducting condi-tion by opening the switch in onebattery lead, but a small delaymust be left before returning theswitch to the on position, or thethyristor will again be triggered.

A 9 or 12 volt supply would besatisfactory. The non -operationalcurrent will be only about 1 milli -amp, so the unit can be left on forlong periods. To conserve batterycurrent, a relatively small buzzer,bell or lamp should be used withthe extension circuit.

CROSSWORD 11941 By DpNEWTON

ACROSS1 A solicitous cartridge?6 A TV hideout?7 A watery way of making

inroads into a coil.9 A means of embedding

information in thecarrier wave.

10 Millicent gives us athousandth but not in thehundred part.

11 Exist.12 Half, often associated

with conductors.13 The brown one is this on

the fence.14 Just a few volts, initially.15 CR circuits may be

used for this minutedevice.

16 Perforated sheet, foundin some valves.

18 Change.20 Could a sloop turn about

in these?21 England, Ireland,

Scotland and Wales.22 Power divided amongst

voltage is extant.23 News travels fast on this.24 To indicate position.25 What we might expect on

a well -tuned TV.27 Useless shortly.28 This gate we would find

prohibitive.

29 The telly would not bethe same without it.

30 To transmit information.

DOWN2 The fashion in headgear

for some valves.

1 2 3 4 5

6

7 8910 11

12

14

15

13

16 17 18 19

22

20

23

21

2427

25 262829

30

3

4

5

6

8

9

10

12

17

18

19

20

212426

28

The spouse in the pushcircuit?There are ratlets aboutin high levelcommunications. (anag.)Resistance movement onHer Majesty's Service.A small flash of lightproduced by a phosphor.No ham could bewithout one.(1,3)Take a tip for thissignal -sorting -circuit.Send the signals in andthey may come out withthese feelings.A coil core of gardeningnotoriety.An LCR circuit gives thisresponse.A one-way street forelectrons.An eggy link from core

to core.Some spots do this inlasting.Loosen.Unattended operation.The signs of high voltagedischarge.Layers of asemiconductor.

Solution on page 513


By Dave BarringtonNew products and component

buying for constructional projects.

This month we seem to have quite amixed bag of products to bring to yourattention.

StickiesIn a recent issue we mentioned the

novel but most practical idea of self-adhesive labels for identifying pinfunctions for a range of some of themost popular 14 and 16 -pin 74 Seriesof TTL integrated circuits.

In view of the low operating currents(typically 100/IA) and ease in whichCMOS integrated circuits can bedamaged, it becomes even moreimportant to know the pin functions ofthese devices. With this in mind it wasonly a matter of time before the pro-ducers of these labels, Concept Elec-tronics, were to market a range of thepopular 4000 Series of CMOS i.c.s.

Specially for the constructor, Con-cept Electronics are making available120 -label sets of STICKIES for bothTTL and CMOS integrated circuits.The CMOS range is made up from 65of the most popular 4000 Series.

Costing 80p per set (120 labels), eachset of STICKIES are packed in a plasticwallet with a data card and instructions.Sets of 480 labels are available and forfurther details readers should contactConcept Electronics, Dept EE, 8 Bay -ham Road, Sevenoaks, Kent.

Drill StandOn the subject of printed circuit

boards and of particular interest tothose readers who make their ownboards, Mega Electronics Ltd., havejust introduced a p.c.b. drill stand foruse with the low voltage hand-helddrill units.

Designa:ed the Photolab PLST-12 A,the drill stand has been specificallyintroduced to meet requirements in theproduction of prototype printed circuitboards. It is constructed with a strongbase of machined cast iron supportingprecision steel guides for raising andlowering the drill.

Boards of up to 254mm x 229mmwill be accepted by the drill stand.

The Mega Photolab PLST-12 A drillstand costs £14.50, plus VAT, and isavailable from Mega Electronics Ltd.,Dept E.E., 9 Radwinter Road, SaffronWalden, Essex CB11 3HU.

Special OfferSome good news for readers from

one of our advertisers this month.Electroni-Kit Ltd., distributcrs of theexcellent Denshi educational kits, havejust introduced a new range they callDenshi EX kits.

To make way for these new kits andto clear existing stocks they are offer-ing readers of EE a special 20 per centdiscount on their SR -1A and ST -45kits.

The SR -1 A contains 16 differentprojects ranging from simple radioreceivers to morse code amplifier. TheST -45 contains 45 projects rangingfrom metronomes to metal detectors.

This offer is only while presentstocks last and readers are directed tothe Electroni-Kit advertisement.

Logic MonitorFinally, for those readers who are

keen on logic circuits and would liketo "see" those mysterious integratedcircuits functioning then the LM -1Logic Monitor from A. Marshall'sshould be a sound investment at£30.99 including VAT.

Suitable for all dual -in -line (up to 16pin) logic i.c.s., the monitor simul-taneously displays the static anddynamic ogic states of DTL, TTL,HTL or CMOS on a 16 I.e.d. display;one for each i.c. pin.

The LM -1 is simply clipped over thei.c. and the I.e.d.s give an instant logicindication; high (1)-I.e.d. on, low(0)-I.e.d. off.

For further particulars write toA. Marshall (London) Ltd.. Dept E.E.,40-42 Cricklewood Broadway, NW23ET.

Printed circuit drill stand from MegaElectronics.

TV Stunt CycleOne of the items called for in the TV

Sturt Cycle game we published lastmonth was a 9V d.c. power supply.

The estimated cost of the design wepublished was just over £3. Since thenhowever, we have found that one ofour advertisers, J. Bull (Electrical) Ltd,is able to supply a suitable ready -builtpower pack for £2-53. Built in a smallplastic case, the unit is listed as aPP3/PP9 Replacement and is suitablefor loading up to 100mA.

If you prefer to build your own powersupply they are able to supply anotherbuild -it -yourself kit, which gives volt-ages of 6, 9 and 12V for loads up to500mA. This kit is listed as a MainsTransistor Pack and sells for just £2.

Co lstructional ProjectsThere are only a few points to men-

tion regarding the constructional pro-jects this month.

We cannot foresee any problemswith the In -Situ Transistor Tester.If readers do not wish to use thetester for in -situ checkouts, then theDIN socket can be dispensed with andthree miniature crocodile clips used tohold the transistors under test.

This is not a new idea and all youneed to do is fasten the emitter, baseand collector wires that would normallybe connected to the DIN socket pins toeach crocodile clip. The clips can thenbe stuck, with impact adhesive, to thefrort panel to form a connecting block.

There should be no difficulty inobtaining parts for the Visual Conti-nuity Tester or the Tele-Bell.

Liciging from readers correspond-ence, the 100W Power Slave amplifierthis month is quite an ambitiousprotect that should prove very popular.Provided the instructions are followedcarefully there should be no problemswith the circuit construction as thedesign uses a printed circuit board.

Some of the components are"specials" and not generally available,but it is strongly recommended thatreaders use only those items specifiedin trie article and components box.

The mains transformer, type 9010(90'1 - 8ohms version), is the mostexpensive item and was designedspecifically for the job. This is avail-able from Zeta Windings, 26 All SaintsRoad, London, W1, at a cost of £16.36including VAT and post/packing.

All the transistors and the diode D6,which is a special forward bias refer-ence type, are available with mostother components from A. Marshall(London) Ltd., Dept EE, 40-42 Crickle-wood Broadway, London, NW2 3ET.

Finally, if like me you are not a dabhard at woodworking, readers will bepleased to know that a completedwooden surround for the amplifier isavailable from P. Daly, 13 CherstonRoad, Loughton, Essex, price £13.60inc.uding postage and packing.


I\ -SITUTRA\SISTTESTER

WITH transistors featuringprominently in most elec-

tronic designs for the home con-structor it is not surprising thattransistor testers are very popularconstructional projects withnumerous designs having beenpublished in the past.

Most transistor tester circuitsare for simple leakage and gaintests or for comprehensive tran-sistor analysers. In either of thesecases the units are intended tocheck a transistor which is not con-nected into circuit.

IN CIRCUIT TESTINGThe transistor checker described

here is a little unusual in that itcan be used to check a transistorwhile it is in or out of circuit.

It must be emphasised that theunit provides only a very roughcheck of the device under test andalthough in most cases it will pro-vide reliable results, under certaincircumstances it c a n provide

By R. A. Penfold

erroneous results, as will beexplained more fully later on.

Despite this, provided the unitis used sensibly with its limitationsbeing borne in mind, it can proveto be invaluable for rapid checkson batches of untested transistorsor faulty transistorised equipment.

LEDINDICATOR

BASE BIASRESISTOR

(a)

CURRENTLIMITING alRESISTOR

TESTTRANSISTOR

OPERATING PRINCIPLEThe basic way in which the unit

tests an npn transistor is illus-trated in Fig. la.

A transistor will not normallyconduct between its collector andemitter terminals unless a suitablebias current is applied to its baseconnection. With the circuit in thestate shown the base of the deviceunder test is short circuited to theemitter, and so no collector/emitter current should flowthrough the device. An l.e.d.indicator is used to monitor thecollector current, and so thisshould not light un at present.

However, if the switch is set tothe other setting a base bias cur-rent will be supplied to the devicevia the appropriate resistor, and acollector will flow which will causethe l.e.d. indicator to come on.

The test circuit for a pnp tran-sistor is shown in Fig. lb, and isthe same as for a npn deviceexcept that the supply rails andl.e.d. polarity must be reversed.

CIRCUIT DESCRIPTIONThe final circuit diagram of the

In -Situ Transistor Tester based onthis idea is shown in Fig. 2.

The manual switching arrange-ment of the basic circuit is re-placed here by an electronic switchwhich "cycles" at a rate ofapproximately 1Hz. Thus, whenthe circuit is connected to a ser-viceable transistor the l.e.d.indicator should flash on and offabout once per second.

An NE555 timer i.c. in theastable mode is used to generatethe 1Hz switching signal. ResistorsR1, R2, and capacitor Cl set thefrequency of oscillation and alsodetermine the mark to space ratio

LEDINDICATOR

BASE BIASRESISTOR

CURRENTLIMITING B1

RESISTOR

TESTTRANSISTOR

MEP

Fig. 1. (a) Testing an npn transistor (b) Testing a pnp device.


of the output waveform. In thiscase the ratio is roughly one toone (i.e. the on and off times ofthe l.e.d. will be approximatelyequal).

PNP MODEIf we consider the circuit in the

pnp mode, the output of IC1 isconnected to the base of TR1 viathe potential divider which consistsof R3 and R5. Transistor TR1 willtherefore be switched hard onwhen the output of IC1 is low, andcut off when this output goes high.

When in the high state the out-put of the i.c. is about 1 to 2 voltsbelow the positive supply railpotential, which normally would besufficient to turn TR1 on if itsbase was simply fed via a seriescurrent limiting resistor, ratherthan by way of the potentialdivider network. Resistor R6 is thebase bias resistor for the transistorunder test.

The emitter of the test transistoris connected to the positive supplyrail through Sld, and the collectoris connected to the negative supplyrail through D1 and current limit-ing resistor R8. The base terminalconnects to TR1 collector throughSla, and so the device under testwill be biased by R6 when TR1 iscut off, and it will be cut off whenTRI is switched on and effectivelyshort circuits the base emitterterminals of the test transistor.

HOW IT WORKS ...

Basically the unit consists of alow frequency oscillator operat-ing an electronic SWITCH. Whenthe SWITCH is closed the baseand emitter terminals of the testtransistor are shorted together.Thus the transistor is turned off.

R ANTIS TOR

UNDERTEST

When the SWITCH is turned on, by the pulses from the oscillator, thebase/emitter is disconnected. Instead the base is connected to a BIASRESISTOR which turns the transistor on. Thus the indicator illuminates. Thefinal result is that the I.e.d. indicator flashes on and off when a goodtransistor is connected.

NPN MODEIn the npn mode the base of the

test transistor is connected to thejunction of TR2 collector and R7.It is then TR2 which short circuitsthe base of the device under test,and R7 which provides the basebias. Transistor TR2 is switched onwhen the output of the i.c. goeshigh and switched off when it goeslow. In the low state the output ofthe NE555 is only a fraction of avolt, and so TR1 can have its basefed from the output of IC1 viaonly a current limiting resistorrather than a potential divider, asin the case of TR1.

GoDAAlck.

04o

44 ESTIMATED COSTOF COMPONENTS

Fig. 2. The complete circuit diagram for the In -Situ Transistor Tester.

£3.50excluding case

R25.6Mil

1.C.1NE 555V

R5Iokn

R3 27k (1

TR1BCI7

R772kfl

Slb

REIkn

S Id

0

TR2R5

S2

(8

Sic0

ftDITIL209

--J

-(CSKI

TRANSISTORUNDER TEST

BI9V


In the npn mode Sld connectsthe emitter of the test transistorto the negative supply rail, andSlb and Slc connect the collectorto the positive supply rail via R8and Dl. These two poles of themode switch also ensure that thepolarity of D1 is appropriate.

Switch S2 is the on/off switch.The quiescent current consumptionof the circuit is about 5mA, thisrising to about 10mA when thedevice is connected to an operativetransistor.

STARTHERE FOR

CONSTRUCTION

CASEA Verobox type 65-3851A makes

an excellent housing for the pro-ject, but any case of a similar size,120 X 65 X 40mm, should also besuitable. The general layout of thefront panel can be seen from thephotographs, but this is notcritical and any layout can be used.

TEST LEADThe connections to the test tran-

sistor are brought out to a 3 -wayDIN socket. Most transistors willplug direct into this socket, butfor those which will not, or whentesting in -situ devices, it is neces-sary to connect suitable test prodsto the unit via a 3 -way DIN plug.

It is advisable to use clip -on typetest prods or sub -miniature croco-dile clips as it would be extremelydifficult to hold three test prods inposition simultaneously.

The DIN socket requires acentral mounting hole 16mm indiameter and this can be madeusing a chassis punch. The posi-tions of the two 3mm diametermounting holes are then foundusing the socket as a template.Short 6BA mounting screws areused.

CIRCUIT BOARDMost of the components are

assembled on a 0.1 inch matrixstripboard panel which has 14holes by 18 strips. Details of the

Completed tester showing front panel layout.

component panel and other wiringof the unit are shown in Fig. 3.

Make the four breaks in thecopper strips and drill the two3mm diameter mounting holesin the panel, then solder in all thecomponents and link wires, leavingthe transistor and i.c. until last.Next wire in R8 and the batteryclip, and complete all the point topoint wiring using thin multistrandp.v.c. covered wire, using reason-ably long leads between the com-ponent panel and the componentson the front panel.

BOARD MOUNTINGWhen all the wiring has been

completed the component panel ismounted on the rear panel of thecase behind diode D1 and the DINsocket. It is mounted using twoshort 6BA bolts, and an extra nutis used over each bolt, betweenthe panel and the case, so that thepanel is just slightly spaced off the

case. If this is not done it ispossible that the panel would bedamaged when the mountings weretightened. The PP3 battery can befitted into the space below the twoswitches, or behind S2.

USING THE UNITAs was pointed out earlier, the

unit needs to be used sensibly if itis to be of maximum worth, and itis not simply a matter of setting Sito the correct mode, connectingthe tester to the transistor, andseeing if the 1.e.d. flashes on andoff.

The following points should benoted;

With germanium transistors it isquite in order for a small amountof current to flow through thedevice even when the base andemitter terminals are shorted to-gether. This current is known asthe "leakage current" and willcause the l.e.d. to glow (but com-paratively dimly) when it shouldbe switched off.

Completed transistor tester with front panel removed showing mounting of the circuit board.

1.


FLAT

TRI&2DI

Fig. 3. Interwiring details for the frontpanel, circuit board component layoutand underside of the stripboard showingbreaks in the copper tracks.

IN -SITUTRANSISTA1,,)RTESTER

oo0000o0 __ 0o 0

"3 0O 0o 0T 00 00 o..--o 0o oo 0O oo 0IIIo oo()00000000000000

-

COLLECTORCOLLECTOR

BASE

EMITTER

Fig. 4. Test lead for in -situtesting using three -core cable,subminiature crocodile clips

1 and a three -pin DIN plug.

COMPONENTSResistors

R1 33k.0R2 5.6MilR3 27ki2R4 27k11All are IW carbon ±5%

CapacitorsC1 3.01µF plastic or ceramic

R5 1042R6 12ki2R7 12kiZR8 1 K2

SeeSemiconductors

IC1 NE555V timer i.c. ShopTR1 BC179 silicon pnp TalkTR2 BC109 silicon npnD1 TIL209 red light emitting diode page 485

MiscellaneousS1 4 -pole 2 -way rotary switch.S2 rotary double pole switch (mains type)B1 PP3 9V batterySK1 3 -pin DIN socketStripboard 0.1 inch matrix 18 strips by 14 holes; Verocase type 65-3851 Aor similar size, 120 x 65 x 40mm; batter/ connector; mounting clip forD1; i.c. socket; two small round knobs; connecting wire; solder; 6BAhardware; additional components for test lead if required: 3 -pin DINplug; flexible stranded wire; three small :rocodile cilps.


IN -SITU TESTINGA similar problem exists when

testing any device in -situ. In vir-tually all instances there will becomponents in the circuit whichwill provide leakage paths and willcause the l.e.d. to glow dimly whenit should be turned off. If thedevice under test is serviceablethere will nearly always be asignificant change in the bright-ness of the I.e.d. as the testerswitches from one state to theother. If the l.e.d. comes on con-tinuously at full brightness thisprobably means the device hasgone short circuit.

Failure of the l.e.d. to come on,or only a continuous dim glowprobably means the test transistorhas become open circuit.

However, before removing anddiscarding a device which has pro-duced such results it would beprudent to check the circuit dia-gram to see if the circuit aroundthe transistor contains any lowresistance paths which could upsetthe operation of the tester. Thesewould normally only occur instages handling fairly high powers,

such as a.f. output stages, and theunit is not recommended for thistype of test.

Reference to Fig. 1 will showthat misleading results could beobtained if there was a short cir-cuit between the collector andbase terminals of the test tran-sistor. This would cause the 1.e.d.to come on when the switch wasin the position shown as the circuitwould be completed through theswitch and the collector - baseterminals of the transistor.

This path would be broken whenthe switch position was changed,possibly causing the l.e.d. to beswitched off. It is therefore advis-able to test the transistor with theemitter test prod disconnected.This should result in the l.e.d. fail-ing to come on except on in -situtests where it will probably lightup rather dimly.

DIODE CHECKINGThe unit can also be used to pro-

vide a quick check on diodes andrectifiers. With a diode or rectifierconnected across the emitter andcollector test prods, with the

Layout of components on the circuit board.

cathode connected to the emitterprod, the 1.e.d. should light upwhen S1 is in the npn mode, andextinguish when it is switched tothe pnp mode.

Readers' Bright Ideas; any idea that is publishedwill be awarded payment according to its merit. Theideas have not been proved by us.

TOUCH SWITCHWhile reading an article in the January issue of

EVERYDAY ELECTRONICS about an electronic touchswitch, it occurred to me that a suitable set of touchcontacts could be made from a phono or similar plug.

The protruding centre -pin is cut to the same levelas the outer cylinder. then smoothed with a file oremery paper. The phono plug is then glued into asuitable hole drilled in the project case.

It is then a simple matter to switch the circuit onand off.

N. Sutcliffe,Manchester

LOCATOR CASEIn the Treasure Locator project (October '77), I

have mounted all the components on a piece of hard-board and fitted an ordinary seed tray on to this. Thetrays without the drainage holes should be used.These are readily available and cost only 20 pence orso. The external controls are simply mounted at oneend of the tray.

A second improvement I have made is using aplastic dinner plate for mounting the search coil, asthis gives a neater finish. Mounted on the plate arethree bolts which connect to the search coil. The threewires from the circuit are terminated in spade tagswhich fit over ,:he bolts. This will prove useful whendismantling.

G. Prynn,Plymouth,Devon.

COTTONTIES

THREE WIRESTO CIRCUIT

ONE OFTHREE TAGS

ref

COIL


Video at the SummitRecently there was some publicity

on how the BBC had started usingelectronic newsgathering techniquesfor television news. In other words,instead of using 16mm film cameras,the BBC is now using video camerasand portable videotape decks.

The first electronic news item wasof Mrs Thatcher. But, seeing their firstefforts, I think the BBC engineersshould take a close look at a remark-able Japanese -Canadian film calledThe Man Who Ski-ed Down Everest.

This film was made a couple of yearsago, but has only just recently reachedthese shores. It records the extra-ordinarily bizarre Japanese expeditionin 1970, led by Yuichiro Miura, toMount Everest.

Eight hundred porters hauled 27tons of equipment up the early slopesof Everest (at a rate of $1 a day for a30 -kilo load I) and seven men went withMiura and two tons of equipment up tothe top of the glacier just below thesummit. It was Miura's ambition to skidown that glacier and, although hevery nearly killed himself in the processthis he actually accomplished.

It's all there in the wide screencolour film, shot with massive Pana-vision cameras that must have madeup a fair fraction of the 27 tons. Butwhat made the trip electronically fas-cinating was the fact that Miura alsotook up a full complement of Akaivideo equipment.

He knew that the 6,600ft long glacierwould provide a frighteningly fast runon skis (well over 100m.p.h.) and sendhim plunging down a ravine at the endunless he could stop in time. So Miuraplanned to use a parachute trailing outbehind him, to slow his ski speeddown a little.

The problem was that parachutesare not designed to operate at thealtitude of Everest which is around30,00()ft, where the air is very thin. So

By ADRIAN HOPEMiura and his colleagues tried someshort, experimental runs with theparachute, filmed them with the videocamera, and then sat down to watchwhat must have been the highest alti-tude video playback ever.

They didn't waste the video equip-ment in between ski runs, as amongstthe porters' baggage was a cannisterof pre-recorded video tapes. For mostof the Sherpas it was the first time theyhad ever seen television. And the pro-grammes? Several episodes of the TVseries Bonanza and a full length ver-sion of The Seven Samurai. Surely thatbelongs in the Guiness Book ofRecords.

Compatibility CheckTo run a calculator or TV game or

small cassette recorder on batteries isoften a very expensive business. A fullset of cells can easily cost £1. It makesfar more sense to use a d.c. supply or"battery eliminator". These cost lessthan a fiver and will very soon repaythe original outlay.

But, beware problems of polarity.Recently noticed that two items ofbattery equipment, one a calculatorand the otter a TV game, both pluggedneatly into the same battery eliminator.But one worked and the other didn't.The reason; each needed an oppositepolarity d.c. supply.

Because so much electronic equip-ment now comes in from the East, withdouble Dutch or inadequate instruc-tions (or none at all) there may be noway of knowing which side of the d.c.input socket is positive or negative. Sotry swopping polarity of the d.c. supplyif a gadget works on batteries but noton an eliminator.

Bear th s in mind when buying (ormaking) an eliminator. You will need apolarity reversal switch to avoid fiddlyand time consuming re -wiring.

My impression is that calculatorsmay tend to have one polarity andrecorders and TV games the opposite.But is this a standard? If it is, no-oneseems to refer to it. Possibly it's just amatter of 50-50 chance which polaritya piece of equipment needs.

A couple more, equally irritating,non-standard situations are arising.There are now several miniature taperecorders on the market which rely onminiature audio cassettes. Thesecassettes all superficially resembleminaturised versions of the well knownPhilips audio cassette but, and it's abig but, they aren't all the same. Infact, there are now three or foursligItly different minature cassetteswhich fit only the machines for whichthey were designed.

So be warned. Although two minia-ture cassettes and recorders may lookcompatible, there is a good chancethat the cassette for one won't quitefit tie machine for another and so on.

L kewise, be warned when buyingmicrophones for ordinary audio cas-sette recorders. Some of these comewith DIN plugs and present no prob-lem. But others have a double minia-ture jack on the end, one half of thejack carrying the audio signal and theother serving the remote on -off switchon the microphone.

The snag is that the spacing be-tween the two halves of the plug maybe such that a microphone for onemachine won't fit another even thoughtheir sockets look exactly the same.So be very careful about buying suchmicrophones by mail order or withoutthe machine itself to hand, so that youcan check for an easy fit before pur-chase.

CLUB CORNERTHE BRITISH AMATEUR

ELECTRONICS CLUBSpecial facilities are now offered by

BAEC to its novice members. A "clearinghouse" has been established, throughwhich beginners can request informationand advice, and receive appropriate helpand even practical assistance in the formof kits, components and books. The BAECNewsletter will contain a new series aimedat the beginner.Secretary: J. G. Margetts, 42 Old VicarageGreen, Keynsham, Bristol.

WALLINGFORD ELECTRONICS CLUBFormed in September 1977, The Walling-

ford Electronics Club is a non-profitmaking organisation for the pursuance ofelectronics as a hobby. The Club exists toprovide mutual exchange of knowledgeand experience in the fields of radio, elec-tronics, electrical engineering and relatedsciences and technology. The club alsoprovides education and encouragement toyounger members who wish to makeelectronics their hobby or their career.Secretary: J. Gilpin, 27 Clapcot Way,Wallingford, Oxon OX10 8HS.


LAST MONTH we saw how informa-tion in a microcomputer is con-

veyed in bytes (groups of 8 bits).Let us now discover how this in-formation is shunted around amicrocomputer to enable it to doexactly what the human user in-tends.

Remember the MPU chip is onlypart of the complete microcom-puter system; it can do nothing byitself because it needs two sorts ofinformation:(1) A complete list of instructionscalled a program that actually tellthe MPU what to do (add, subtract,multiply or divide, for example).(2) Data or "numbers" on which toperform these instructions.

These two kinds of informationare stored in two kinds of memory-we are going to call these justprogram memory and datamemory respectively for themoment (see Glossary). Thesememories are usually contained inseparate chips - referred to as"peripherals".

BUSES OR HIGHWAYSWhen instructed by the MPU

itself, either of these memoriescan unload bytes of information.They communicate with the MPUby means of buses or highwayswhich transfer information andcontrol signals from one part ofthe system to another. There are

commonly three main buses in amicrocomputer system:

(1) Data bus.(2) Control bus.(3) Address bus.The term data bus may confuse

-it not only transfers data butalso instructions! It's a two-way(bi-directional, in the trade jargon)bus, that is, by crafty design, wecan use the same signal lines to putinformation into and take informa-tion out from, the MPU.

The control bus as its name im-plies switches the peripheral chipsto the MPU on and off in sequenceto ensure for example that more

MICROPROCESSORUNIT

(MPU)

than one memory doesn't use thesame bus at the same time. Under-standably, this would cause theMPU some confusion!

But all this wouldn't be muchuse if the MPU didn't know wherethe information it wanted waslocated in the memories. And thisis where the address bus comes in.Each byte in each memory isassigned a unique label or addresswhich performs exactly the samefunction as our own houseaddresses-they tell people wherewe are.

When the MPU outputs thebinary address of a memory loca-tion it uses the address bus toactivate the right one and dis-gorge its contents on the data bus.

For an 8 -bit MPU the addressbus is usually of 16 -bit capacity,i.e. it can address up to 216 or 65,536separate locations.

You can visualise the memoriesas stacks of "pigeon holes" inwhich each instruction is storedneatly next to the following one.This makes for a logical programread-out when the contents of eachare examined in turn by the MPU.

INSIDE THE M.P.U.Fig. 2 shows schematically the

important parts of the MPU itself.Again note that nearly all the

internal components have access toone or other of the main externalbuses. The MPU also possesses itsown small storage registers, themost important of which is the 8 -bit accumulator, the main store ofthe MPU were data is arithmeticallymanipulated (for example, addedtogether) to produce results.

DATA MEMORY(VARIABLES STORED)

(RAM)

PROGRAM MEMORY(INSTRUCTIONS

STORED)(ROM)

OPM101,41,11.

ADDRESS BUS (I6 -BIT UNIDIRECTIONAL)

Fig. 1. A basic microcomputer system, including MPU and memories.


ACCUMULATORARITHMETIC ANDLOGIC UNIT (ALU)

INSTRUCTIONDECODER

INSTRUCTIONREGISTER

PROGRAMCOUN-ER

Fig. 2. A schematic diagram of the inside of a microprocessor.

The 16 -bit program counterholds the address of the next in-struction to be drawn from the(program) memory. After each in-struction is completed it is auto-matically incremented by 1 and sokeeps track of the progress of theprogram.

Other major components includethe arithmetic and logic unit (Aix)which actually performs the addi-tions (etc) and logical operationson the incoming data; and theinstruction decoder which actuallyinterprets the meaning of an 8 -byte instruction for the rest of theMPU.

There are also other miscel-laneous registers concerned with

GLOSSARY

instructions and addressing andtiming circuits which properlysequence the operations of theprocessor.

PROGRAMMING EXAMPLEWe can now follow the operation

of a microcomputer in action. Itis important to realise that eventhe simplest calculations as far ashumans are concerned (forexample, a simple addition such as2+3=5) involve the micropro-cessor in many separate steps. Butwe can summarise its basic opera-tion as being one of fetching bytesof data (in this case the numbers2,3) from the data memory, addingthem together in the accumulator

ACCUMULATOR. The main register or store in themicroprocessor chip.

ADDRESS. The particular location of a data element ina memory store.

ARITHMETIC AND LOGIC UNIT (Aw). The com-ponent in the microprocessor chip which performs thearithmetic (e.g addition and subtraction) and logical (AND,OR) functions on data.

BUS. A data highway to which several components orperipherals have access.

HARDWARE. The physical construction of the computer;i.c.s, memories, displays, etc.

HEXADECIMAL. A number system with base 16, effec-tively a shorthand form of standard binary much used byprogrammers. Decimal and hexadecimal nomenclature isthe same for 0 to 9, but decimal 10 to 15 becomes hex Ato F.

HIGH LEVEL LANGUAGE. A computer language sohighly developed that programs can be written almost inEnglish using it.

DATABUS

) ADDRESSBUS

LOAD ACCUMULATORWITH CONTENTS OFADDRESS X (i.e.2)

ADD TO ACCUMULATORCONTENTS OFADDRESS Y (i.e.3)

STORE ACCUMULATORCONTENT INADDRESS Z

OUTPUT CONTENTSOF ADDRESS 2 TODISPLAY

NEXT INSTRUCTION

Fig. 3. Flow diagram of MPU operations forsimple addition 2 + 3 = 5. The number 2 isstored in data memory address X. Thenumber 3 is stored in data memory addressY. The result is to be stored in data memoryaddress Z. (X, Y, and Z can be any locationsin memory).

(the "add" instruction is of coursesignified by the "+") and thenstoring the result in anothermemory location for future refer-ence, for example, display.

This is summarised in Fig. 3, aflow diagram which ismeans for breaking down pro-grams into their essentials.

OPERATION SUMMARYDescribing the full operation of

a microcomputer system, i.e. whathappens instruction by instruction,is a very long-winded procedure.

MACHINE CODE. Basic microprocessor language,straight binary.

MICROCOMPUTER. A general term referring to asystem containing a microprocessor and support i.c.s suchas memories.

MICROPROCESSOR (met)). The "brain" of a micro-computer, a circuit capable of highly advanced calculationability.

PROGRAM. A complete list of instructions that tells theMPU what to do with its data.

RANDOM ACCESS MEMORY (RAM). A type ofmemory usually used for implementing data memory i.e.the MPU can read information in it.

READ ONLY MEMORY (Rom). Implements programmemory. Information once stored in it cannot usually bealtered by the MPU.

SOFTWARE. A general term for computer programs (asopposed to the computer's physical construction, hard-ware).


ETC.

98

99

100

101

102

ETC.

PROGRAM MEMORY

Fig. 4. The MPU uses program counter register to address program memory.

What basically takes place how-ever is relatively straightforward.The MPU fetches instructions fromits program memory, interpretsthem in its instruction decoder andthen executes them. The numberof permissible instructions for amodern microprocessor is in therange 70-100, quite large enoughfor all the possible data manipula-tions that can take place.

This "fetch -execute" cycle canbe broken down into sub -operations. The MPU in factaccesses instructions in the pro-gram memory by addressing them,location by location in turn via itsprogram counter.

Only when each instruction hasbeen acted on by the MPU is theprogram counter incremented by 1to address the next location (Fig.4). The program memory also con-tains the addresses in the datamemory of the data, i.e. "num-bers" on which these instructionshave to be performed.

INTERRUPTSWe extend the data and

address buses through "input/out-put ports" to the outside world,so with the right devices (forexample tele-typewriters) we can

MAIN PROGRAMe.g. GIVING DRIVER

DIRECTIONS TODESTINATION

SUBSIDIARY INFORMATIONAVAILABLE TO DRIVERTHROUGH MPU ON AUTOMATICINTERRUPTe.g. ENGINE TEMPERATURE?

FUEL AVAILABLE?SPEED?

Fig. 5. The Car of the Future?

OTHER INFORMATIONAVAILABLE ON DRIVER -REQUESTED INTERRUPTe.g. ESTIMATED TIME OF

ARRIVAL ATDESTINATION

"talk" to the MPU and it can com-municate with, and even control,external equipment.

A particularly important featureof this communication is the pro-vision for interrupt signals. TheMPU can after all carry out in-structions in mere microsecondsbut the outside devices it is dealingwith, for example teleprinters, arerelatively slow by comparison.

So we can squeeze the mostusage out of the MPU (and this isthe important thing in any com-puter system) if we operate two ormore of these peripheral equip-ments seemingly simultaneously,but in fact by fast switching, oneat a time.

We can even run the MPU norm-ally through a main program andonly break off what it is doingwhen a peripheral device signals"interrupt". When the MPU hasdealt with the peripheral in ques-tion it can rejoin the main programagain exactly where it left off.

Fig. 5 and Fig. 6 show howfuture in -car and domestic micro-processor systems may be able tomultiplex themselves to give agreat range of "simultaneous"facilities, with such techniques.

WHAT'S IN IT FOR US?"Big deal," you may say. "We

can add two numbers together bymicrocomputer. But we can addthem with a simple logic circuit,too. What have we gained?"

Apart from the small size andpower consumption of the MPUand the fact that we could prob-ably do upwards of a hundred -

thousand of these additions everysecond, what we've really gained(as we hope you've realised) isversatility. A dedicated binaryadder is an adder all of its days,but give a different program to amicrocomputer and it can do adifferent job entirely.

We may find the same micropro-cessor chip in a counter/timer, asewing machine, a piece of testgear, a robot -controlled car or ina calculator. The functions of theseequipments are all different butthe principles of their operationare basically the same.

"ISN'T PROGRAMMING TOOCOMPLICATED FORMOST PEOPLE?"

The programming in machinecode can be a long and tedious


ANCILLARY PROGRAMSe.g. ELECTRONIC TV DAMES

CENTRAL HEATING CONTROLLER1111. MONITORS INDOOR TEMPERATURE

AND OPTIMISES ENERGY EXPENSE

BURGLAR ALARMAVAILABLE BY IMMEDIATEAUTOMATIC INTERRUPT

1OF MPU OPERATION

HOUSEHOLDMPU FIRE ALARM

CALCULATOR IIIINFORMATIONSTORE MAIN MPU COMMUNITY

BUSES TO CIVIC SERVICESPOLICEFIREAMBULANCELIBRARY etc

Flo. 0. Is this the House of the Future?

business and it won't make micro-computers many friends.

However computer engineers-fiendishly clever as they are-have simplified it enormously. Wecan "talk" to the processor inmnemonic words rather than exclu-sively binary. These mnemonicwords are translated into machinecode by the computer system forthe MPU.

If you have a large computerhandy you can even use a reallysophisticated language like FOR-TRAN or BASIC in your programs.It will translate the high levellanguage into MPU type machinecode.

"WHAT DO I NEED TOSET UP A MICRO-COMPUTER SYSTEM?"

Most manufacturers markettheir own MPU "low cost develop-ment kits" aimed at getting thesmall user interested. They containall the essentials needed to get abasic microcomputer functioning-typically the MPU chip itself plusmemory and interface i.c.s and allthe terminal equipment necessaryto enter the display data.

It's this equipment which can be-come the most expensive part ofthe whole system. The ideal input/output or terminal devices areprobably the teletypewriter or

visual display unit (VDU) butthese are probably too costlyfor most people (although buildinga VDU is now certainly withinscope of the home enthusiast).

Fortunately the manufacturershave got round this to some extentat least by supplying calculator -type keyboards and displays toenter and display programs. In thecheaper type of development kitbanks of switches and 1.e.d.s per-form the same function.

So if your pocket stretches to it-or if you can club together witha few friends at school or collegewhy not take the plunge and setup your own computing system? I=1

JACK PLUG & FAMILY... BY DOUG BAKER

WHILE YOU WERE GETTING READY WE. PLAYED THECATCH -A -LIGHT GAME, AND MIKE AND I BEAT DADEVERY TIME. HE'S REALLY SLOW AT SWITCHINGTHE LIGHTS ON

I SHALL HAVE TO BOOK YOU.YOU'RE DRIVING WITHOUT

YOUR LIGHTS ON.


RADIO MODULATIONTHIS month we continue with the subject of Radio.

RADIO WAVESThe possibility of radio waves was glimpsed by

Michael Faraday, worked out theoretically by hisyounger contemporary, James Maxwell, and laterdemonstrated by Heinrich Hertz.

Faraday said nothing about his ideas except thathe wrote a mysterious note which said, in effect, "I'vegot an idea that electromagnetic fields could be usedfor communication, but I haven't time to investigatethis now." He never did.

According to one of his biographers Faradayprobably visualised the field of a magnet Fig. 9.1, aslines of force curving outwards into space like someinvisible, weightless array of wires. The arrayextended to infinity.

If a line of force could be plucked like a harpstring the vibration would travel out into space alongthe line. An observer at some distant point along theline could, in principle, detect the vibration. Thevibrations could therefore be used to transmit in-formation.

To transmit electrical energy required changes ofboth voltage and current. As we have seen, currentis always associated with a magnetic field. Voltageis associated with an electric field. Both kinds of fieldcan extend into space. If both are varied, in sympathy,power is transmitted. This is what happens in radiotransmission.

ey

"YuroNGEoRGE

RECEIVERS

Fig. 9.1. The field of a bar magnet is represented here by thecontour lines of ever -widening diameter.

ELECTRIC FIELDSAt the receiver you can pick up either the magnetic

part or the electric part or both. The coil on yourferrite rod responds to the magnetic field, whichinduces a voltage. An aerial wire responds to theelectric field. In effect, the aerial joins together pointsin space where the voltages are different, so that acurrent flows in the wire.


The electric field and the magnetic field are alwaysat right angles to each other. If you could see thesefields with your eyes and you looked at a radio trans-mitter with a vertical aerial the electric field wouldbe vertical and the magnetic field horizontal. Such atransmission is said to be vertically polarized, thedirection of the electric field shows the polarization.

Radio waves travel through empty space at thespeed of light. This is not surprising because lightis just a very short -wavelength (around half amillionth of a metre), electromagnetic wave.

The speed in air is only very slightly less. In moresolid media it may be much less. Although the speedof electromagnetic waves is high, 300 million metresper second, their passage can be timed by fast elec-tronic timing methods. Time intervals down to abouta thousand -millionth of a second are fairly easy tomeasure nowadays.

A wave travels about 300mm in a nanosecond.To return to your radio receiver, Fig. 7.12. It is of a

kind which used to be called an 0-V-1. That meansthere is no (0) amplification of the incoming radiofrequencies, one detector stage (V) and one audioamplifier stage (1).

You will have realised, no doubt, that the ferrite -cored aerial coil and its capacitor, CT form a parallel -tuned LC circuit which gives selectivity. You may wellalso have realised that the selectivity is not very good.

If you remove the tuned circuit and just connectan aerial Fig. 9.2, and a resistor to discourage mainshum you will be able to see what happens when there

Fig. 9.2. By connectingjust an aerial to the inputof an amplifier, interestingresults can be obtained.

is no selectivity at all. You can use as long an aerialas you like for this experiment.

One thing you are likely to pick up is the local TVsignal. You may also hear short wave signals.

SUPERHETERODYNE RECEIVERSGreat selectivity is needed to pick out weak stations

from among strong ones on frequencies close by.For many years the standard way of improving

selectivity has been to make use of the fact that itis easy to change one frequency into another. Thestrategy is to change the frequency of the wantedsignal to a standard frequency called the intermediatefrequency. The receiver has highly selective filtersset to pick out the intermediate frequency.

The method of changing the frequency makes useof an effect called intermodulation. When two fre-quencies are fed to a device such as a diode or tran-sistor, which does not obey Ohm's Law, two morefrequencies are generated. These are the sum of thetwo original frequencies and their difference.

Thus if the two original frequencies are 10kHz and1 IkHz the new frequencies are 21kHz and 1kHz. Thehuman ear does the same thing. This is why, whenyou hear two ]cud sustained musical notes close toone another in frequency you also hear a third note.

This is a low frequency throbbing noise, thedifference between the two notes. It is called a beatnote or beat tone.

An a.m. transmitter modulated with a single purenote shows this intermodulation effect. In additionto the nominal frequency, called the carrier frequency,sum and difference frequencies are generated. If thecarrier frequency is 1000kHz and the modulatingfrequency is 1kHz the sum and difference frequenciesare 999kHz and 1001kHz.

These fall syn-.metrically on each side of the carrierand are called side frequencies. When the carrier ismodulated by speech and music, which consist notof single frequencies but mixtures of frequencies awhole series of side frequencies is generated on eitherside of the carrier. These side frequencies are knowncollectively as sidebands.

DETECTIONThe process of detection is also an intermodulation

process. When applied to the detector, the carrier andside frequencies give rise to different frequencies.

In the example quilted each side frequency beatswith the carrier to produce a side frequency of 1kHz.This of course is the original audio frequency, whichis thereby recovered by the detection process. Whenintermodulation takes place the strongest signal isdominant. In amplitude modulated signals the carrieris always at least twice as powerful as the sidebands.So the sidebands beat with the carrier, not with oneanother.

To change the frequency of an incoming transmis-sion to the intermediate frequency the usual type ofreceiver uses a local oscillator. Its output is fed tothe intermodulation generator called the frequencychanger along with the incoming station Fig. 9.3.

1000kHz

AERIALTUNING

LOCAL

OSCILLATOR

FREQUENCY

CHANGER

1SOOkHz

INTERMEDIATEFREQUENCY

FILTER500kHz

TO I FAMPLIFIERANDDETECTOR

Fig. 9.3. Simple block diagram of a superhet receiver. Theimportant section to note is the frequency changer.

IMAGE FREQUENCIESOne snag about the system is that there are always

two signal frequencies which can beat with the localoscillation to yield the wanted i.f. In the examplegiven, this other signal frequency is 2000kHz Fig. 9.4.

The aerial tuning circuit has to be selective enoughto eliminate this unwanted other frequency calledthe image frequency or second -channel frequency.

This is not very difficult for the frequencies shown.Other signal frequencies near the wanted frequency

also beat with the local oscillator to producedifference frequencies.


IFWANTEDSIGNAL[ ,000

SIDEBANDS

LOCALOEC

1500

IMAGESIGNAL

t't

2000 kHz

Fig. 9.4. Illustrating how image signals or second channelfrequencies can be produced.

These fall on either side of the chosen i.f. and arerejected by the i.f. filter. Sum frequencies are alsogenerated and similarly rejected.

This kind of receiver is called a superhet, which isshort for "supersonic heterodyne". Here heterodynemeans beat frequency and supersonic means too high-pitched to be audible.

Your kind of receiver, with tuning only at theincoming radio frequency is called a tuned radio fre-quency receiver. Practical t.r.f. receivers usually in-corporate positive feedback to improve selectivity.

TODETECTOR

Fig. 9.5. The principal of a t.r.f. receiver. This circuit isessentially the same as an LC oscillator.

The principle Fig. 9.5, is essentially the same as inan LC oscillator, but the feedback is adjustable. Tomaximise selectivity the receiver operator sets thefeedback control so that the circuit just fails tooscillate. Since the LC aerial circuit has an impedancewhich is highest at the tuned frequency, the feed-back via R1 is greatest at this frequency, which isemphasised most.

The general effect is shown by the dotted curve inFig. 9.6. The feedback, usually called reaction orregeneration increases gain as well as selectivity.

IMPEDANCEOF

TUNEDCIRCUIT

to (tuned freq)FREQUENCY

Fig. 9.6. Graph showing how the Impedance of a tunedcircuit varies with frequency.

MODULATIONA radio transmitter sending out a steady frequency

is not a very effective communicator. You might saythat the only information it is sending out is that itis switched on! This is true in spite of the fact thatlots of change is in progress, the waves emitted gothrough their regular cycles of positive and negative.

However, all these cycles are identical. Lookedat in terms of Francis Bacon's code, if you call apositive half cycle A and a negative half cycle B thenthe transmission is an endless alternation of A'sand B's.

No matter how you divide this up into groups offives (or any other number for that matter) it justgoes on repeating the same code.

To convey more information it is necessary to varythe signal in some way. The simplest is to switch thetransmitter on for A and off for B. Thus the trans-mission pattern for A B B A A would have a short"on" period, a double -length "off" period then adouble -length "on" period. Fig. 9.7.

A

ON I OFF ON CODE

TRANSMITTEDWAVEFORM

Fig. 9.7. Switching a transmitter on and off for certainperiods, a code such as A B B A A can be sent. In this wave-form the code is sent as a series of waves.

This sort of code involves precise timing. It is nottoo bad for teleprinters, where the timing dependson the design of the machine. Even then, however, itis usually necessary to transmit an extra A at thebeginning of the sequence to mark the start of asymbol and an extra one to mark the end.

CW TRANSMISSIONHuman beings are not at all good at reading this

sort of code and they hate having to work at anabsolutely steady, machine -like pace. So, in theMorse code, which was designed for human operators,the task of distinguishing between time intervals ismade easy. There are short intervals, dots and longones, dashes.

The transmitter is turned on for both dots anddashes. So the international distress code, the SOSsignal, consists of three dots, three dashes, and threedots. Fig. 9.8.

"0" -STRANSMITTEDCODE

CODE ASRECEIVED

Fig. 9.8. The top waveform is a perfectly transmitted morsecode signal. The bottom waveform Is the shape sometimesreceived on a distant receiver.

So long as the human recipient of the message candistinguish between dots and dashes, and also recog-nise the complete sequence as one meaningful codethe desired information is successfully received.

Also, it does not matter if the on pulses are ratherrounded, the lower pattern is still quite recognisable.


This kind of Morse transmission is usually calledcarrier wave transmission. The carrier wave is thenominal frequency of the transmitter. Strictly speak-ing, of course, a broken up or pulsed transmission isnot a pure carrier wave at all. It should be given someother name such as pulsed carrier wave, or inter-rupted carrier wave.

The basic characteristic, however, is that thestrength of the transmitter is varied according to thesignals transmitted. In a Morse transmission thetransmitter is just turned hard on or hard off. Youcannot get a bigger variation in strength than that.Morse code does not have to transmit signals of vary-ing strength, it is a binary system in that respect.

Speech and music are very different. Their strengthvaries all the time, and of course their frequencyvaries too.

AMPLITUDE MODULATIONTo transmit sound by making the strength of the

transmitted waveform vary in sympathy needs thesort of waveforms shown in Fig. 9.9. The transmitteris turned on all the time, even during silent periods.

SIL ENCE

APPLIED MODULATION

111111 0104 11101111Fig. 9.9. An audio waveform as depicted by the upper curve isapplied to a carrier as in the lower curve. As can be seen theaudio is "carried" both by the negative and positive sides of thecarrier.

The sounds make the strength of the carrier increaseor decrease. This enforced variation is called modu-lation, and the strength, in engineering terms, isamplitude. So we end up with amplitude modulation.

SIDEBANDSIf a complex sound signal is analysed it is found

to consist of mixtures of sine waves of different fre-quencies, which add or subtract to produce the com-plex wave. Each of these sine waves, when it modu-lates the carrier wave, produces two new frequencies,one above and one below the original frequency.

A 1kHz sine wave signal modulating a 100kHzcarrier creates frequencies of 99kHz and 101kHz aswell. Note that these new side frequencies differ fromthe carrier by the audio frquency. To transmit a10kHz audio frequency, additional frequencies of90kHz and 110kHz are generated. To transmit all fre-quencies up to 10kHz fills the band between 90 and110kHz. This bandwidth is 20kHz, just twice thebandwidth of the audio signals.

This is wasteful. In effect, the audio is transmittedin duplicate, once above the carrier frequency andonce below it. Also, the carrier itself, as we sawearlier, conveys no information.

If the carrier and one sideband are removed, andonly the other sideband is transmitted, we have asingle sideband signal, s.s.b. In the example above,the s.s.b. signal for 1kHz modulation on a carrier of100kHz is 99kHz (lower sideband) or 101kHz (uppersideband).

SINGLE SIDEBANDSingle sideband is used a great deal for commercial

purposes and by radio amateurs but not for soundbroadcasting. The reasons for this become clear whenyou examine the receiving end of a communicationssystem. To illustrate :he point we shall use an ampli-tude -modulated signal. Fig. 9.10.

Here the audio is a sine wave shown dotted, andthe carrier frequency is the waveform inside theaudio envelope.

TI E

7 7

Fig. 9.10. A modulated carrier is shown at (a). To recover the audiofrom this, samples are taken at regular intervals as shown by (b).The samples thus p'oduced d.c. pulses, which can then be "filled"in to farm the audio.

To recover the audio from the a.m. signal you haveto sample it at each, say, positive peak, this isrepresented by the second graph. The samples arethen d.c. pulses as shown by the third graph. Theirheights follow the shape of the audio wave. It is veryeasy to fill in the gaps between samples.

The usual way is to use an RC time constant. Ifthe sample pulses are pulses of current these can beused to charge a capacitor. A resistor discharges it,slowly enough to retain most of the charge from onesample to the next, but quickly enough to allow thestored voltage to follow the audio variations.

Normally, the carrier frequency is much higherthan the audio, so there is no difficulty in finding atime constant which can fill in the gaps withoutaffecting the audio.

FREQUENCY MODULATIONThere is another common method of impressing

information onto a carrier, that is used widely in v.h.f.and u.h.f. systems, including TV sound.

This is called frequency modulation or f.m. forshort. Unfortunately we do not have the space to dis-cuss this particular method in the present series.

(a)

Ic)


BEAT FREQUENCIESBy now, many of you will be wondering why all

this fuss is being made about sampling. Surely, youare asking, all you need to do, to get the audio back,is rectify the transmitted signal? If half wave rectifi-cation is used the output is as shown in the last graph.This is obviously a mixture of d.c., audio, and thecarrier frequency.

With ordinary a.m. signals like this it is easy. Butwhat about single sideband, signals? In s.s.b., asteady modulation at a fixed audio frequency producesa pair of steady side frequencies, each unvarying inamplitude. Rectifying one of these, Fig. 9.11, pro-duces d.c. only, and no audio.

(01

1 _A (b)

TIME

Fig. 911. For recovering the audio from s.s.b. signals (a), samplesmust be taken at different Intervals as in (b). The output samplesnow go both positive and negative to produce a low frequencysine wave.

To produce audio, you have to sample at a differentrate, as in the second graph (b). The output samplesnow rise and fall and go positive and negative (c),and clearly have a low frequency sine wave in them.What frequency?

Well, this obviously depends on the difference be-tween the side frequency and the sampling frequency.The bigger the difference the faster the samplingtimes go in and out of phase with the s.s.b. signaland the higher the output frequency. What is hap-pening is the production of a beat frequency betweensignal and sampling frequencies.

We need a beat frequency which is equal to theoriginal audio frequency at the transmitter. If youthink about it, you will find that to remake theoriginal audio, the sampling frequency must be theoriginal carrier frequency. This is the one samplingfrequency which produces the correct audio fre-quency from any side frequency.

You can now see the virtue of transmitting thecarrier frequency of an a.m. signal. When the com-plete a.m. signal is rectified the carrier makes therectifier conduct at just the right instants; the peaks.

For s.s.b. reception a frequency equal to theoriginal carrier must be generated at the receiverand used to control the sampling process. This isknown as "re-inserting the carrier". How exact needthe reinserted carrier frequency be?

Suppose, as is commonly the case, the originalsound is not a pure tone but also contains harmonics.Say 300Hz with a second harmonic at 600Hz and athird at 900Hz. If the locally generated carrier is inerror by 50Hz, the effect is to change each of thesefrequencies by 50Hz.

So instead of producing 300, 600 and 900Hz youget, 350, 650 and 950Hz. These false frequencies areno longer harmonically related. The true harmonics

of 350Hz are 700 and 1050Hz. The effect of this is tomake the sounds of speech and music take on apeculiar croaky quality and become less intelligible.

To keep the frequency correct calls for a verystable local oscillator. If the true carrier frequencyis 10MHz and the permissible error is 10Hz then thisrequires a frequency accurate within 1 part per mil-lion (1Hz in 1MHz). This is a very stringent require-ment, difficult to meet. A possible way out is totransmit, along with the s.s.b. signal, a carrier smallin amplitude, cften called a pilot carrier. This can bepicked out and amplified and used to reconstitute themissing carrier.

PRACTICAL RECEIVERIt is all very well discussing the theory of modula-

tion etc, but the best idea is to actually hear thedifferent types. To do this some type of receiver isnecessary. A suitable design is shown in Fig. 9.12.This receiver covers part of the medium wave bandbut goes on to cover the lower short wave bandsas used by shipping, commercial users, and radioamateurs etc. This part of the frequency spectrumis often called the Trawler Band. The exact coverageobtained depends on the coil and tuning capacitor.Basically however we want you to use the receiverto experiment.

CONSTRUCTIONThe covercard required for the receiver module is

shown in Fig. 9.13. No problems should be encoun-tered in construction, however a few points need tobe observed.

The coil is homewound on a large insulated former,in our model we found a cylindrical container whichonce contained pills. If no container of suitable sizecan be found then a substitute can be made by rollingseveral layers of paper together to make a stiffformer. The former is about 38mm in diameter andabout 90mm in length, the actual length is not toocritical.

The larger coil, Ll, has 45 turns of ordinaryinsulated wire, and the coupling coil L2 has 5 turnsof the same wire wound about 20mm from the oneend of Ll, see Fig. 9.13.

Capacitor C2 need only be a few picofarads in valueand we make it ourselves, by connecting short lengthsof stiff insulated wire to the top of LI and TR2collector then twisting them together as shown onthe layout diagram.

The two conductors are plates, and the insulationis the dielectric. The more twists the greater thecapacitance.

As will be mentioned later the two coils, LI andL2 and capacitor C2 may need slight adjustment toobtain a satisfactory coverage. It is advisable there-fore to wind a few extra turns on both coils, so thatlater separate windings can be easily removed. It isfar easier to remove turns than to add extra!

Once constructed and, as always, checked for anymistakes, a battery may be connected. The audio out-put from this simple circuit is not really largeenough to drive a loudspeaker direct, so take the out-put to the input of the POWER AMPLIFIER.


SHORTWAVE

RECEIVER

R

027 Ai:

L7-1 C 7

I100pr

Fig, 9.12. Circu t diagram for our Short Wave Receiver.

T81

9V I

SHORT WAVE RECEIVER

.111111111=1UL

ly()

at-nion--0

3.3k0

300pF 100ka

TUNE REACTION

Fig. 9.13. Covercard required for the receiver. This is shown full size and may be traced.


OPERATIONSince the receiver relies on positive feedback it

needs careful adjustment. Positive feedback (reactionor regeneration) exaggerates differences betweentransistors, battery voltage, etc. The circuit consistsof a radio frequency amplifier, TR1 followed by adiode detector D1 and D2.

Positive feedback is controlled in two ways. First,C2 is a preset reaction control which feeds part of thesignal back from the collector of TR1 to the tunedcircuit Cl, Ll. The two coils Ll, L2 form a trans-former and by connecting the right end of L2 via C3to the base of TR1, positive feedback is obtained.

The other reaction control is VR1, which suppliesbase bias current to TR1. Reaction is usually mosteffective at the high frequency end of the tuningrange and least effective at the low frequency end.

To adjust C2, turn VR1 fully clockwise and adjustC2 so that the circuit just oscillates. This is heard inthe loudspeaker as a whistle which varies in pitch asa station is tuned in. If you get a steady whistle allthe time it means you have too much reaction.

The adjustment of C2 is made with an aerial andearth connected. A short vertical aerial (half ametre of wire) can be connected to point Al. If youlive in a steel -framed building or other difficult loca-tion you may have to use a longer aerial connectedto point A2.

The earth connection should ideally be buried inthe ground but a water pipe, radiator or any largemetal object in the house is better than nothing.

REGENERATIONA good regenerative receiver works without "back-

lash". That is, it should be possible to turn up thereaction control so that the circuit slides gently andimperceptibly into oscillation. A bad circuit will sud-denly burst into uncontrollable oscillation and youhave to turn down the reaction control a long way tostop it.

Your receiver should behave itself if C2 is set cor-rectly. If it does not, but gives the sort of behaviourjust described, remove a few turns from L2 and re-adjust C2. If you still cannot get any oscillation atall but still pick up a few stations it probably meansthat L2 needs its connections reversed.

If there is a fault somewhere, check with yourVOLTAGE INDICATOR. The collector should be at almostlice when the slider of VR1 is anticlockwise, fallingto above 2V when it is clockwise.

The two diodes conduct alternately to form a sortof full wave rectifier.

The components RS, CS and C6 form a storage andsmoothing circuit to remove the radio frequencyripple.

Diode detectors must have a d.c. load, which hereis R4. Resistor R6 and C7 are not strictly necessary.They form a decoupling circuit to prevent feedbackfrom the power amplifier, which can upset the re-action, especially when the battery is old and tired.

You can add or remove turns on LI to adjust thetuning range, C2 must be readjusted after any majorchange. When all is correct you will find yourself inthe fascinating world of shortwave reception, a world

full of whistles, buzzes, clicks, Donald Duck speechnoises, and foreign programmes.

If you use an outside aerial, earth the downlead(the connection to the set), outside the house inthundery weather for safety.

ZERO BEATOne effect worth looking for is synchronisation of

a weak oscillation in your receiver with an incomingcarrier. If you lune in very slowly the beat frequencysuddenly drops to zero. This is a tiny "dead zone",or null in which you can change the tuning withoutproducing a beat. In this zone the incoming carriertakes charge.

Another phenomenon is "hand effect". Putting yourhand anywhere near the circuit when it is in a sensi-tive condition has an audible effect. This is proofthat electric fields extend into the air, but otherwiseit is just a nuisance.

Bringing a piece of metal, for example, a coin, nearthe coil when the set is oscillating has an effect onthe frequency, audible as a change in a beat note.This is used in one kind of metal detector to revealburied metal. You will find that the detection rangeis very short. This is because the magnetic field ofthe coil diminishes rapidly as you go further away.

Next month we shall introduce the subject of Logic.

QUESTIONS9.1. A superhet receiver tuned to 2.7MHz experi-

ences "image" interference from a second trans-on 1-3MHz. The receivers intermediate

frequency is;a. 465kHzb. 700kHzc. 1.4MHz

9.2. In C.W. transmission the carrier wave is;a. the frequency of the transmissionb. the code transmittedc. the sidebands

9.3. An a.m. t-ansmitter sending on 800kHz is modu-late() by a steady 1kHz signal. The frequenciestransmitted are;a. 800kHz onlyb. 799kHz and 800kHzc. 799, 800 and 801kHz

9.4. An s.s.b. transmitter on 3MHz sends the lowersidebands. When modulated by a steady 2kHzsignal the frequencies emitted are;a. 3MHz and 2.998MHzb. 2.998, 3.0 and 3.002MHzc. 2.998MHz

9.5. Which frequency is supersonic (ultrasonic);a. 30kHzb. 3kHzc. 30Hz

ANSWERS(To part 8)

8.1. 40W (c)

8.2. 20V (b)

8.3. 180' (a)

8.4. 200mA (b)

8.5. 140V (a)


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LOGIC PROBEUsing one i.c. and associated components, this pocket-sizeinstrument can be useful for tracing faults in projects, and fortesting ex -computer i.c.s.

SHORT WAVERADIO

Tuning from around 3MHz to 16MHz, this simple t.r.f. receiveroffers the constructor an introduction into the fascinating worldof short wave radio.

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Flg. 1a. The circuit diagram of the power supply section of the 100W Power Slave.

shown in Fig. lb which is seen tobe a full complementary directcoupled amplifier with output shortcircuit protection.

Input to the amplifier is at SKIand the input signal appears acrossVR1 which acts as a volume con-trol. A second socket SK2 is wiredin parallel with SK1. This is notintended as a second input,although it could be used as such,but is a means of linking to anotherpower slave input.

The wiper of VR1 is coupled tothe base of TRla via d.c. blockingcapacitor C4. TR1 is arranged to

form a differential amplifier whichis a convenient means of settingthe d.c. voltage level at the outputto OV, enabling the amplifier to bedirectly coupled to the loud-speaker. D.C. stability is accom-plished by means of 100 per centfeedback from the output to theinput by resistor R6.

The ratio of 116 to R5 governsthe closed loop a.c. voltage gain.Zener diode D5 is used to set thed.c. current through the differen-tial amplifier and provide a.c. humrejection from the negative powetsupply line.

Transistor TR5 serves as a con-stant current source for the d.c.bias current which flows throughTR3 and the dual bias diode D6.This diode has been selected todrop the precise amount of voltage(between the bases of TR6 andTR8) to bias the output stage tothe verge of conduction.

The resulting output from thedifferential connected pair (collec-tor 1) is directly coupled to thebase of TR3 connected as a highgain common emitter amplifierwhich feeds the two compoundpairs in the output stage, TR6/7and TR8/9. As can be seen thesefunction as emitter followers whichprovide high current gain withunity voltage gain. Therefore, TR3must be capable of handling thefull load voltage swing (peak -to -peak).

The positive portions of thesignal are handled by TR6 andTR7 with the negative excursionsbeing dealt with by TR8 and TR9.

The amplified signal is fed tothe output sockets SK3 and SK4wired in parallel through emitterresistors FI15 and R16 and a chokeLI.

The latter is incorporated in thecircuit together with resistor R30to dampen the output responsewhen feeding highly capacitiveloads (e.g. hi fl speakers incorporat-ing cross -over networks).

Flg. 1 b. The circuit diagram of the audio amplifier section of the 100W Power Slave Incorporating electronic short-circuit protection.

1-4-34V,415V)

SKI

(INPUT)

SK2

Fir4'71

CtKipF

-34,o

OS

R7

7004

TC307SIPSUSSR2TR3

9(MPSUS21

TR1MDB001

PAD80031

R35.1811

75

CO

".700pF

3901227007

PA

560ti 2.41,

96 *K.;

TR4B57237

50pF

D6+10239

TR5uPSu06

I mPSJ5

9137000

a

TR6MPS JO 6N4P6u071

TR7Aso:

077.50

917 8(0(520123

R150.3912

919

2.2kA,

9212.2.0

990)

R2633012

TRIOuPst.ci

iE

4'5'02(2: R27 929

3101; 20(1

928R24 3302.

6.14,

SKI

*SEE TEXT


100

90

80

30

OUTPUTPOWER 60(WATTS)

50

40

30

20

10

0

0 0.4 08 12 16 20 2.4 28 32 36 l0NORMALIZED LOAD IMPEDANCE

Fig. 2. Maximum obtainable output power as a function of loadimpedance. The normalised load is obtained by dividing thespeaker impedance by the nominal load, 4 or 8 ohms. (Motorola).

A Sobel network composed ofR29 and C9 are included forreasons of stability when feedingreactive loads.

SHORT CIRCUITPROTECTION

The short-circuit protection net-work active components compriseTRIO, TR2 and D7 for positiveportions of the output signal andTR11, TR4 and D8 for negativeportions. The protection networkhas been designed so as not tointerfere with a "normal load"under worst case conditions whichoccurs when there is phase shiftof 60 degrees between voltage andcurrent. This is particularly thecase in hi fi speaker systems wherethe load can appear highly capaci-tive or inductive as well as resis-tive.

For positive half cycles of thesignal, resistors R17, R19, R20 andR21 form a voltage summing net-work. The voltage appearing at thebase of TRIO is determined by thevoltage drop across R15 (which is

+0.5

0

OUTPUTPOWER 05( dB I

10

15

200-01 C -I 10

FREQUENCY (kHz)10 20

Fig. 3. The output power as a function of signal frequency into aresistive load; 0dB represents 100 watts r.m.s. (Motorola).

proportional to the current flow-ing in TR7 and therefore into theload) and the voltage between thepositive supply rail and the output.Since this arrangement detectsboth current and voltage, it effec-tively senses the peak power dissi-pated in TR7.

The values of the componentsin the summing network havebeen calculated with the worstcase conditions mentioned abovetaken into consideration to causeTRIO to turn on when the peakpower dissipation in TR7 x posi-tive rail voltage x maximum powercurrent flow) is exceeded. WhenTRIO conducts, its collector movestowards OV and turns on TR2which steals the drive current fromthe base of TR3 and hence limitsthe power dissipated in TR7.

Similarly for negative excursionsexceeding the predetermined level,TR11 conducts which in turncauses TR4 to conduct. This shutsdown TR5, the constant currentsource, thereby limiting the dissi-pation in TR9.

Zener diode D7 is included to

TYPICAL PERFORMANCE FIGURESOutput Power

100 watts r.m.s. into 4 ohms or 8 ohms (dependent on version built)Input Sensitivity

775mV into 10 kilohms for full outputFrequency Response

Less than 3dB roll -off from 10Hz to 100kHz referenced to 1kHzPower Bandwidth

100 watts r.m.s. ±0 5 from 20Hz to 20kHzTotal Harmonic Distortion

Less than 0.2% at any power level between 100mV and 100W at any frequencybetween 20Hz and 20kHz

Intermodulation DistortionLess than 0.2% at any power level from 100mV to 100W (60Hz and 7kHz mixed 4to 1)

Damping FactorGreater than 150 at any frequency from 20Hz to 20kHz ;Motorola)

prevent TRIO from conductingunder normal load conditions whenthe output swings negative; D8 hassim:lar action on positive outputswings.

The protection network will alsooperate if the nominal supply linevoltages are exceeded by 10 percent or more.

OUTPUT PERFORMANCEThe circuit has been designed

to operate under any load condi-tions including a short circuit, butmaximum output will only beobtained for a precise load, in thiscase 4 or 8 ohms according to theversion built. The graph of Fig. 2shows the output power as a func-tion of the impedance of the loadas a result of the inclusion of theprotection network. A power-band-wid:h graph is shown in Fig. 3.

CONSTRUCTIONThe majority of the components

are mounted on a printed circuitboard. In the prototype fibreglassboard was used but this is notessential.

The pattern to be etched isshown full size in Fig. 4a.

A lmm drill will be suitable formost of the holes but those allo-cated to resistors R15, R16, R29and R30 may need to be enlargedas these leads can be quite thick.Use is made of Veropins as thesemake wiring up much easier as willbe seen later. The board fixingshould be drilled for 4BA clear-ance.

Begin by assembling the resis-tors and capacitors according toFig 4b. Inductor Ll is made by


Fig. 4,' The underside of the printed circuit board shown full-size. The black areas are the regions of copper to remain afteretching.

TR7

ti -:-.7%

Q= VEROPINS

+34V11-4551VIA F52

OV (SOLDER TAGON Ti CHASSIS)

SK3EARTH TAG

SK3SIGNAL TAG

Fig. 4b. The layout of the components on the topside of the p.c.b. together with wiring information to other components.


winding 20 s.w.g. enamelled copperwire the full length of resistor R30and soldering the ends to the resis-tor leads close to the body. Nextinsert and solder in position theVeropins.

Finally position and solder thesemiconductors paying specialattention to polarity and connec-tion details, see Fig. 5.

Close inspection of some of thetransistor cases will reveal that thelead connections are printed on thebody. This is not so with theMD8001 (MD8002) and this mustbe orientated with reference to thetag on the body. It is wise to usea heatsink on the leads of thissemiconductor to prevent thermaldamage.

The author found that theleads on the Uniwatt transistors(MPSU06, MPSU07, MPSU56 andMPSU57) have very thin leadsand are easily sheared, so becareful to bend the leads correctlyfirst time. The driver transistorsTR6 and TR8 require heatsinks. Itis best to position these on theboard and then secure the heat -sinks before soldering. A layer ofheatsink compound between thetab and heatsink will produce amore efficient thermal contact.Mica washers and insulatingbushes are not required formounting TR6 and TR8 as long asseparate heatsinks-not in contact,are used as in the prototype.

0

TR2,TR4

b

TR7,TR9e b c

TR3 TR5,TR6,TRI3

Fig. 5. Shows lead -out details of the semi-conductors specified. All are viewed frombelow with the exception of the Uniwattdevices which are seen facing the colouredbands on the body.

e 0 0b

TRIO,TRII

METAL TAB

POWER HEATSINKSThe power output stage heatsinks

should next be drilled to accom-modate TR7 and TR9. Also drillthe heatsinks for mounting to thechassis with 2BA clearance holes.

It is imperative that the outputtransistors be mounted using amica washer and insulatingbushes, see Fig. 6. The collector

COMPONENTS -74701Resistors

R1

R2R3R4R5R6R7R8R9R10All watt carbon filmwise. (*wirewound)

Capacitors

68052 R11 1.2k52 R21

10kfl R12 68 (10on) R225.1 kit R13 10011 R235.6kfl (8.2K1) R14 1000 R2439052 (2705I) R15 0.3911 5W R2510k12 R16 0-3912 5W R261000 R17 1kfl (51012) R27100 R18 1kf2 (51052) R281005 R19 8.2kf2 (9.1k52) R29331d1 (39k0) R20 2.2k12 (1.8142) R30

47012470512.21d1 (1.8k11)8.2kfl (9.1 k51)330P3301233052330521012 2W1012 2W

or metal oxide +5% except where stated other -

C1 4700/4F 50V elect. radial tag C6 100/2F 10V elect..C2 4700/LF 50V elect. radial tag C7 50pF ceramicC3 0.1µF plastic or ceramic C8 50pF ceramicC4 10/2F 6V elect. C9 0.1/4F plastic or ceramicC5 0.1,uF plastic or ceramic

SemiconductorsTR1TR2TR3TR4TR5TR6TR7TR8TR9TRIOTR11D1 - D4D5D6D7D8

MD8002 (MD8003) dual transistorBC307 silicon pnpMPSU56 (MPSU57) silicon pnpBC237 silicon npnMPSUO6 (MPSU07) silicon npnMPSUO6 (MPSU07) silicon npnMJ4502 silicon pnpMPSU56 (MPSU57) silicon pnpMJ802 silicon npnMPSLO1 silicon npnMPSL51 silicon pnpPW01 6A 100V bridge rectifer400mW 10V ZenerMZ2361 silicon forward reference7.5V 400mW Zeier7.5V 400mW Zeier

MiscellaneousVR1 10k52 log. carbonT1 9010 (9011) ma ns primary/50V 5A (65V 3.5A) centre -tappedS1 mains on/off toggle [secondarySK1, 2, 3, 4 standard jack socket (4 off)LP1 mains panel mounting neonFS1 1A 20mmFS2, 3 5A (3.5A) 20mm (2 off)PL1 panel mounting 3 -pin mains plugPrin:ed circuit board size 160 x 102mm; 20mm panel fuseholder forFS1; 20mm chassis fuseholders for FS2, 3 (2 off); heatsinks: Redpointtype 4W and CH77 (2 off each); TO -3 mica washers and insulatingbushes (2 sets); vertical mounting capacitor clips for C1 and C2; 5Aconnecting wire; screened cable; 18 s.w.g. aluminium for chassis;rubber grommets (4 off); 4BA threaded spacers 25mm long for p.c.b.mounting (4 off); 2BA nuts, bolts and washers (10 sets); 4BA fixings:bolts, washers (16 off), nuts (8 off), solder tag; 6BA nuts, bolts andwashers (6 off each); 6BA solder tags (2 off); materials for front andrear panels (metal), base panel and case; Veropins.

silicon npn

diode

See

VACpage 485

Values and type numbersin parenthesis refer to the

8 ohm version only

connections to each output tran-sistor is at the case and this ismade via a solder tag under oneof the transistor fixing nuts.

Attach ample lengths of heavyduty insulated wiring to each tran-sistor connection. A mechanicaljoint prior to soldering is advised.Use different colours for each of

the six leads for easy identificationwhen wiring to the p.c.b.

Dimensions, drilling details andshape of the main chassis are shownin Fig. 6; 18 s.w.g. aluminium wasfound to be suitable. Three sets ofwires will be fed through thischassis and each feed hole shouldbe fitted with a rubber grommet.


35 20 10

122

50761 -

25

300

IS

MICA WASHER

BOLT

ut.ttimmnm Ill

TR7,9

DRILLING DETAILS

A= IBA CLEARANCEB= 2BA CLEARANCEC= 9mm DIA.ALL DIMENSIONS IN mm

Fig. 6. Drilling and bending details for the main chassisassembly, 18 s.w.g. aluminium is a suitable material. Alsoshown are the fixing details of the output transistors ontheir heatsinks. Use heatsink compound on the inter-faces for good thermal contact.

Feed the wires from each transis-tor through to their appropriatehole and bolt each heatsink to thechassis. Now secure the p.c.b. tothe chassis using 4BA bolt/washersand threaded spaces and then wireup the output transistors to theboard at the Veropin anchorpoints. Make mechanical jointsprior to soldering. This applies toall other Veropin connections. Thisassembly, to be called the mainchassis assembly is complete andcan be put aside until later.

POWER SUPPLYDetails of the power supply

chassis are shown in Fig. 7 and isagain made from 18 s.w.g. alu-minium. This also acts as a heat -sink for the bridge rectifier. Mountthe capacitors in their clips andsecure to the chassis using 4BAnuts, bolts and shakeproof washers.Do likewise with the bridge recti-fier and fuseholders and wire upaccording to Fig. 7 using heavyduty insulated wiring. The supplyline wiring is passed through afeed hole in the chassis whichmust be fitted with a rubber grom-met. Do not insert the fuses intotheir holders at this stage.

FRONT PANELDrilling details for the front

panel are included in Fig. 8. Inthe prototype this was made from4mm plywood and after the fixingrail had been fitted using counter-sunk screws, was covered in blackFormica to produce a hard glossyfinish. Self-adhesive labels with

si

I

Fig. 7. Dimensions and drilling details for the power supplychassis with complete wiring up details. This has been drawn"flat" for reasons of clarity. This chassis is held in place on thebase panel by four self -tapping screws.

DRILLING DETAILS

A= 2BA CLEARANCEB -SELF TAPPING

SCREW POSITIONS

ALL DIMENSIONS IN mm

8

NYLON BUSH

SOLDER TAG

/In'/WASHER

NUT

HEATSINK


eo

130

40

o"DOWELPOSITION

As

DRILLINGDETAILS

9 DIA.13

11

12

13

ALL DIMENSIONS 'AT rnm.

FROM r.FIN i4

I

FROM /PIN B

VRt (6-1

20

es_43

\ DOWEL; POSITION

SKI

FIXING RAIL

20

352

125

Fig. 8. Shows dimensions and drilling instructions for the front panel showing positions of components (viewed from rear) and connectiondetails to other components. Aluminium or steel plate is recommended in place of the plywood employed in the early prototype shown inthe photograph.

Letraset were used to identify thefront panel controls.

Assemble the components onthe front panel and wire the pairsof sockets in parallel as shown. Donot make any other connections atthis stage.

BASE PANELIt is now necessary to make the

base panel. Drilling details of thisare shown in Fig. 9. The eight largeholes are ventilation ports for theoutput transistors, the heatsinkssitting directly above.

The transformer fixing holes are2BA clearance and are positionedto suit the specified transformer,and may need to be altered tosuit other types that may be used.These holes need to be counter-sunk on the underside as do themain chassis fixing holes to allowthe base plate to sit squarely onthe base of the cabinet sleeve. Bolthead clearance recesses are re-quired under the power supplychassis which is held in place by6mm long self -tapping screwsthrough the chassis into the base.

ASSEMBLYFix the transformer in place

followed by the power supplyassembly. Note that one edge isbolted to the transformer framefor rigidity reasons. Note also thatthe upper fixing is fitted with a2BA solder tag to act as the mainearthing point. Next bolt the mainchassis in place.

The back panel ( having the samedimensions as the front panel) is

IS 15

-490 4,1

I

aa 45

"4-30 30 30

DRILLING DETAILS

2BA CLEARANCE 63-4- -aB.. 25mm DIA.C - SELF TAPPING

SCREW POSITION

ALL DIMENSIONS IN mm 89

A A

25

t

fi/4) ///' %fie

90

300

30 30

125

%NI

REAR PANEL FIXINGBRACKETN

50

90

255

T19

V

1.11 90

Fig. 9. Dimensions and drilling instructions for the base panel which in the prototype wasconstructed from 9mm thick plywood. Note that the rear panel fixing rails are shown screwedin place.

fitted with a 3 -pin panel mountingmains plug, see photograph.When this has been constructed,the wiring up can be carried outaccording to Figs. 4, 7 and 8 andthen the front and rear panelsfitted to the base panel by meansof self -tapping screws through thefixing rails. Note that the upperfixings of the back panel areattached to the case one in eachtop corner and the back panel issecured to the transformer frame.

When the wiring has been car-ried out and thoroughly checked,the amplifier is ready for testing.A mains lead needs to be builtup terminated in an insulatedshrouded socket to suit PL1.

TESTINGDo not insert the fuses FS2

FS3 at this stage. Plug intomains and switch on at Si.neon should light. Measure

andthe

Thethe


power supply output voltage levelsat the input sides of FS2 and FS3with respect to earth. On FS2 thevoltage reading should be +34V( +45V) and that on FS3, - 34V( -45V) or up to 10 per cent more.

If all is well, the amplifier shouldbe switched off and FS2 and FS3inserted. Care should be exercisedhere as the smoothing capacitorswill be charged up, and could givea nasty shock if touched. It maybe as well to discharge them firstusing a resistor of about 200 ohms.

With the fuses connected, noinput signal, and no speakers orother load connected, switch onand measure the voltage at the out-put socket. It should read OV orvery close to this. If all is well aspeaker load can now be con-nected. Do this with the amplifierswitched off. With power back onthe voltage across the speakershould still read OV. A signal fedinto SK1 should be heard in thespeaker and become louder as VR1is advanced.

It only remains to check theshort circuit protection. This canbe done by wiring a heavy dutyon/off switch in parallel with thespeaker load. With a signal passingthrough the system operate thisswitch. The sound from thespeaker will of course disappearbut sound should return when theswitch is turned off.

Space does not allow details ofthe case to be given, but a photo-graph of the prototype case isshown above. This may of course

The finished prototype 100W Power Slaveremoved from Its cabinet.

ine 11`..

Photograph of the prototype main chassis assembly corn-pletpd and ready for installation on the base panel. Obser-vant readers will note that TR1 has been replaced by twoTO -18 type transistors, BC109's in fact, as these were tohand at the time of construction. This substitution wasfound to have no adverse effect on performance.

Photograph of the prototype sleeve -typecabinet. This was constructed from 13mmchipboard with triangular batten formingthe front lip. The finished amplifier is fedin from the rear and held in place by thecabinet feet fixings. This cabinet is avail-able ready built as shown, see Shop Ta/kfor details.

be changed to suit individual tastesbut it is important that ventilationgrills be included in the design andfor these to be sited directly aboveand below the output transistorheatsinks.

Also the cabinet base must beraised to provide an air passageto the lower grill. This is accom-plished by using about 25mm highplastic feet on the base. The fixingsfor the feet in the prototype werelong enough to also serve as thebase panel fixing screws. 1c1

Next month we shall be taking a lookat pop, disco PA and hi fi systemsusing a 100 Watt Power Slave.


EncapsulationI have recently encapsulated a small

radio in Plasticraft liquid plus hardener.I thought this would be an ideal way tostop components from coming adrift.

However the radio after a time ceasesto work. Could this be due to some typeof screening effect? Incidentally only thecomponents, not the aerial, were encap-sulated.

I would be interested in your commentsor if anyone else has tried this. If in factit does work, there must be possibilitiesif vibration is likely to occur in the useof any project.

P. G. Sherwood,Manchester.

The idea of sealing electronic circuits is ofcourse well known in the professionalareas, but is not used widely in the amateurarea.

We see no reason why the radio shouldnot work because of any screening effect.Only metal would completely screen anyradio waves. It is possible then that thesealant has caused some damage to thecomponents themselves.

Have any readers any ideas on this? Anyideas will be welcome and be consideredfor publication.

Light DisplayI have just built the Chaser Light Display

in the February issue, and have found thefollowing modifications very worthwhile.

By adding four single -pole switches inseries with the wipers of S4 and the junc-tions of the I.e.d.s and base resistors, amore versatile display is achieved. Insteadof the basic two patterns, we have four.

H. Bowker,Sandy,Beds.

Photograph of the RTV31 taken at Erith,by Mr. Cooper.

Photoflash SocketIn the Photoflash Slave Unit in the

December '77 issue, a flash socket wasrequired. It was said in Shop Talk thatthese are not generally available, howeverI have found at my local shop, a socketmanufactured by Kaiser Foto Technik.

Their pack number is 1327, and the pricewas E1-02. This could be cheaper thanbuying the extension lead from Dixons assuggested.

N. Mortimer,ly`iInthorpe,

Cumbria.

Clunk -Click TripI should Ike to draw readers' attention

to an inprcvement to the "Clunk ClickJogger", circuit No. 13 in the PopularCircuits feature.

Some readers may experience difficultyin preventing spurious firing of CSR1when the car engine is running. All seemswell until the engine is started whereuponthe device would fire spontaneously.

Although my prototype did not sufferfrom this defect and was tried on a fewvehicles, it seems that some cars tend toproduce excessive noise from the charg-ing circuit and the spikes tend to fire theCSR through capacitor C1.

This defect was corrected by reducingthe value of C1 to 0-01µF instead of 0.1µF.This, of course, would also occur in caseswhere C1 was on the high side of its toler-ance.

T. R. de Vaux-Balbirnie,Huntingdon.

LoudspeakersFirst may I compliment Mr. J. Smith on

his excellent article on loudspeaker enclo-sures in the February '78 issue.

However, I am surprised that no mentionhas been made concerning the "phasing"of the speakers. This means that thecones of a:l three speakers move in thesame direction at the same time. And not"one in -one out" so to speak. As this wasnot mentioned, The project may be a dis-appointment to the beginner.

It is a good idea to mark all one'sspeakers with the correct polarity forfuture reference. A simple way of doingthis is to use a 14 volt battery, connectedacross the speaker coil. If the cone movesout, then the positive of the battery isconnected to the positive of the speaker.

Finally I would like to say that the authoris quite right when he implies that thequality will be unexpectedly good.

J. W. Robson,Newcastle upon Tyne.

Cranfield Place. The ContinuingStory ...

I must agree with Mr. U. F. Wood thatTracked Hovercraft Ltd., was not atCranfield, see letter in the February issue.

The Institution of Mechanical Engineers,Railway Division, paid an official visit tothe site and installation of T. H. Ltd., atErith, Cambridge in April 1972 at whichI was privileged to be present.

Enclosed is a copy of the Institutionnotice and the notes, handed out at thetime, about T. H. Ltd., together with acouple of not very good photographs ofthe experimental vehicle taken on the day,which you will note is identified RT V31and not TSR2.

P. C. Cooper,Derby

Mr. Hope replies . . .

I enclose a strip of negative film (seephotographs-Ed.) showing on the samestrip wo shots I took at Cran field, one of thetracked hovercraft and one shot of the Good-year airship.

The fact that both shots are on the samestrip surely proves that I haven't taken leaveof my senses. I really did see both the airshipand the tracked hovercraft at Cranfield onthe same dayl -Were there two RTV31's?

By the way the TSR2 (unless / mis-remem-ber the code word title) was a very fast lowflying aircraft.

Crossword No. 4-Solution

rj1 I ,C K U 3I) a E0A U 'SCREENTtY; P L G LF iz/LLI S

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Mr. Hope's photographs, showing on the left the RTV31 at Cranfield. On the right the Good-year airship-also at Cranfieldl


Everyday NewsA NEW TESTIMONY

BY ELECTRONICSIt is not often that an electronics magazine is invited to a

film premier, but this is what happened when the film, TheSilent Witness, produced and directed by David W. Rolfe forScreenpro Films, was first shown in London recently.

The film traces and investigates the amazing history of theHoly Shroud of Turin, which millions believe was used tocover Jesus after the crucifixion.

Displayed to the public only three times in the last hundredyears, the 14ft long and 3ft wide Shroud is kept behind barsin Turin Cathedral. Recently, however, leading internationalscientists and scholars were allowed to examine the Shroudfor the first time and The Silent Witness presents, exclusively,the results of their research.

Some of the questions facing the investigators were asmysterious as the cloth itself. Why is the image a photo-graphic negative? Why does it possess anatomical and medi-cal detail centuries ahead of its time? This is where elec-tronics plays an important part in the investigators' findings.

For an analysis of themedical evidence on theShroud, the film crewtravelled to Los Angeleswhere they have the busiestand most modern forensicmedical centre in the world.The chief forensic medicalexaminer, Dr. R. Bucklin, atAustin, Texas, reconstructedthe exact manner of deathof the man on the Shroud.

A team of American scien-tists from the AtomicWeapons Research Labora-tory and the US Air ForceAcademy also produceddramatic discoveries usingelectronics.

On one research projectUS Air Force physicistsfound that the image is en-coded with 3.dimensional in-formation that can recreatea perfect 3D picture on acomputer screen-no otherpainting or photograph, itclaimed, in the world pos-sesses this quality! Thesupervisor of image enhance-ment at the Jet PropulsionLaboratory and responsiblefor the analysis of the pic-tures sent back on the MarsMariner space mission, Dr.D. Lynn, subjected the imageon the Shroud to a frequencyanalysis to detect any form

of "directionality' or handpainting - results show,graphically, that it cannotbe the product of a humanhand!

Together the scientistsconclude that the only causeof the image that will fit thenew data on the Shroud is amicro -second burst of intenseradiation.

We found the film a verypersonal and moving experi-ence and all credit to its pro-ducers in that it leaves theaudience to form their ownverdict. Unfortunately, at thetime of going to press, thefilm is to finish its run in

London and although it ishoped to move it to anothercinema no definite date hasbeen finalised. Also, it ishoped to show The SilentWitness in other parts of thecountry.

* The latest information wehave is that the film is beingput on to 16mm and will beavailable for hire to any in-terested parties. Details canbe obtained from the dis-tributors, Namara Entertain-ments Ltd., 18b WellingtonCourt, Knightsbridge, LondonS WI.

PARIS COMPONENTS SHOWThe 21st Salon International Des Composants Electroniques

was held in Paris from 3 to 8 April.This year special emphasis was given to quality of products,

and prototypes of components having obtained the CECC(CENELEC Electronic Components Committee) certificatewere on display in a special stand.

The CECC includes representation from 11 European coun-tries, and is responsible for establishing norms, specificationsand procedures with which the certified components mustcomply.

The French equivalent of "Viewdata" known as ANTIOPE(Acquisition Numeriques et Televisualisation d'InformationsOrganisees en Pages d' Ecriture) was in operation andattracted much interest.

Thirty different nations were represented amongst the totalof 1,200 firms exhibiting. The UK had the 4th largest contin-gent, with 87 participants. These included all the big namesin the UK semiconductor industry, and a variety of firms inthe passive component, solder, materials and hardware busi-ness.

Kits for home constructors were displayed by severalFrench distributors. Also on show with its French name Dis-cosonn, was the Chroma-Chime microprocessor -based doorchimes.

After successfully launch-ing hobby computers in theUSA last year, Heathkit haveintroduced them to the UKmarket.

Name DroppingA link with the past was

broken when the nameElliott was dropped fromMarconi -Elliott Avionic Sys-tems Ltd. The company isnow to be known as Mar-coni Avionics Ltd. and itsAmerican associate as Mar-coni Avionics Inc.

The name of Elliott hasbeen in the title since 1969when Elliott Flight Automa-tion and Elliott AutomationRadar Systems came intothe Group. Marconi Avionicshas now grown to 9,000people employed, with

equipment used in some 150different types of civil andmilitary aircraft.

Transatlantic DateThe Post Office transatlan-

tic Packet Switching Serviceis due to start on July 1. Itenables computer data to betransmitted both ways be-tween the USA and the UKin "packets", providing sub-stantial cost savings.

Tornado RadarThe air interception radar

to be fitted to the air defencevariant of the Tornado air-craft now being built for theRoyal Air Force will have atarget detection range of100 miles. Its Skyfiash mis-siles can be engaged on tar-gets at a range of 24 miles.


from the World of Electronics

Engineers' SalariesThe average chartered

electrical engineer's salary,according to a survey carriedout by the Institution ofElectrical Engineers, in-creased by only 5 per centlast year, well below thenational average. This repre-sents an increase from£5,890 to £6,210 p.a.

An interesting statisticemerging from the surveyis thai the predominant fieldof employment for IEEFellows, Members and Asso-ciates is now electronic ortelecommunications equ i p-ment development or manu-facture and not, as one mighthave assumed in the IEE, inheavy electrical engineeringor electricity generation anddistribution.

Military OrderIn conjunction with Cinct-

natti Electronics Inc of theUSA, Marconi Space and De-fence Systems has won a de-velopment contract for theUS Army SINCGARS-V(Single Channel Ground/ AirRadio Systems VHF).

This is the first time aBritish company has beenable to compete on levelterms with US contractors.The development cr.-Atract isworth $6 million and it issaid that if successful thefollow-on production ordersmay amount to as much as250,000 equipments.

The 19 - member ArabLeague is spending about£10 million in consultancyfees to Comsat General Cor-poration to advise on a com-munications satellite systemfor Arab States. The systemwill be called Arabsat.

The Impactof Electronics

The keynote address to theLondon conference, The Im-pact of Electronics, by JackAkerman, Managing Director,Mullard Ltd., has been re-printed in an attractive bro-chure with illustrations ofhistorical interest. The storyconcludes with a happy pros-pect for blind persons, whomay be able to see with theaid of synthetic eyesight bythe year 2000. This kind ofachievement makes elec-tronics truly the great ser-vant of man.

Copies of this booklet areavailable from Central En-quiry Handling Unit, MullardLtd., New Road, Mitcham,Surrey.

A new department hasbeen set up by PostOffice Telecommunications toaccelerate the development ofSystem X, the all -Britishelectronic exchange equip-ment that, it is claimed, willrevolutionise the nation'sphone system.

TOMORROW'SBROADCASTING

A few points from a lecture by Dr. Boris Townsend, of theIndependent Broadcasting Authority, delivered at the IBAlast February.

MECHANISMS INTO MICROCIRCUITS"Mechanisms grow more and more expensive to produce,

while electronics become cheaper and cheaper. Compare the£70 monochrome television receiver, of dubious performance,which sold in 1938, with its contemporary £100 small motorcar: and then take today's large, bright, reliable monochrometelevision receiver, still at £70, and its contemporary £2,000Mini. So whenever we can replace mechanisms by electronicswe shall."NEW STUDIOS

"In the future, real background scenery will be unnecessary,although super -stars will probably insist on having it. Toyscenery and chroma-key techniques will do, with computercontrol of the scenery camera, which looks into the minia-ture stage through a periscope, keeping the perspective ofthe background correct as the foreground camera is crabbed.After a few years, even the toy scenery will disappear. The

ANALYSIS

MOST SECRETSecret written codes are known to have existed for over

2,000 years but it wasn't until the invention of the telephoneand, later, the radiotelephone, that systems had to be in-vented to make voice communications secret because tele-phone lines can he tapped and radio transmissions monitored.Speech scramblers, as such systems are popularly known, havebeen mainly used by governments, security services andarmed forces but, today, industrial espionage has reachedsuch proportions that many business firms are now usingsimilar equipment.

In fact, what used to be a comparatively small esoterichush-hush back -room activity has now blossomed into anindustry in its own right called Communications Security,covering not only voice but data communications andfacsimile.

So, over the years, there has been a build-up 01 move andcounter-move. On the one side, big spending on increasinglysophisticated message encryption systems, on the otherequally big spending on means of defeating the systems,generally by using huge number -crunching code -breakingcomputers.

The big advances of recent years are entirely due to elec-tronics, in particular digital electronics and large scaleintegration (LSI) which have enabled very complex systemsto be built in quite small packages and at reasonable cost.One commercially available equipment, for example, is builtinto an ordinary document case. With it you can go into apub ic telephone :all -box and providing the person you arecalling has decoding equipment you can have a conversationsecure from eavesdroppirg.

The same firm makes a tiny encoder which can be clippedon to a military manpack radio so that even a platoon sergeantin the front line or battle can report back to his commanderswith freedom from intelligible reception by enemy monitoringstations.

Brian G. Peck

scenery camera will look at a flatly lit photograph of therequired background and. the graphics computer will adjusta perspective and 'he shadows of the transmitted image asrequired."

TOMORROW'S TELEVISION SET"By the 1980s we can also expect the domestic television

receiver to be as much a computer visual display unit as itis a television set and television will face more competitionthan does radio. Micropracessors will turn this colour VDUinto an indoor games centre."

WHAT IS POSSIBLE?"Our technology has reached a rather exciting stage-a

very democratic stage-an open stage. 7'elevii.ion researchengineers have some powerful technologies at then disposaland organisational methods which enable them to more fastin meeting a demand. The question is no longer 'What ispossible?' We have to decide between a bewildering arrayof possibilities."

ENERGY SAVING"Perhaps the most significant teelmirel development in tele-

vision has already been mane --in ten years we have reducedthe power consumption of domestic receiters by two-thirds;this saves, every night 700 megawatts, or enough electricityto rescue 100,000 old people from hypothermia."

"It is no longer a question of what can the engineers do?It is a case of what will the programme makers of the 1980swant? What will the Governments of the 1980s permit? Whatwill the public of the 1986s pay for? Who will tell es?"


VISUAl

TIO

I T Is often required to be able todo a quick continuity test,

usually a simple battery and bulbcombination will suffice. It is how-ever, limited to a circuit with aresistance not exceeding 100 ohmsresistance or thereabouts.

It is with this idea in mind thatthis circuit was formulated. Thebasic idea is that the tester candifferentiate between various typesof resistive circuits.

CIRCUIT DESCRIPTIONThe circuit of the Continuity

Tester appears in Fig. 1, and as

E-3

can be seen is very simple. Threeindicating devices are provided,the first, LP1 is connected inseries with a resistor of 22 ohms.

This part of the circuit is ableto provide an indication of the con-tinuity in circuits where the "con-tinuity resistance" is less than 100ohms (Low).

The second indicator Dl is alight emitting diode with its serieslimiting resistor and can just beseen to illuminate when only 0.2milliamps flows, therefore beingable to indicate when the "con-tinuity resistance" is any value upto about 39 kilohms (MEDIUM).

1C1By A. Sproxton

For continuity through highervalued resistances an amplificationstage is required, and this isaccomplished by means of TR1which is loaded with the third in-dicator D2 (HIGH), a similar lightemitting diode to Dl. The "con-tinuity resistance" forms the baseresistor in series with R3.

GAINAccording to manufacturers

data, the minimum gain of a BC108transistor is 120. Now the currentrequired for the l.e.d. to be illu-minated is, as we have seen earlier,


COMPONENTS -1'7

ResistorsR1 220

All 4W carbon 4-10%ValtR2 5600R3 27042

page 485

See

O

SemiconductorsTR1 BC108 silicon npnD1 TIL209 green light emitting

diodeD2 TIL209 red light emitting diode

MiscellaneousLP1 6.5V 0.06A I.e.s. bulbPL1, 2 2mm plugs (1 red, 1 black)B1 PP3 9V batterySK1 to 6 2mm sockets, black (3 off),

red, green, white (1 off each)Plastic case, size approximately 115 x75 x 50mm; battery clip to suit B1;flexible wire for test leads; two croco-dile or other clips; connecting wire;mounting h irdware for I.e.d.s and LP1;6BA solder tag.

GODANCL.o,

%0. ESTIMATED COSTOF COMPONENTS

£2.00excluding case

II 1 SK3

IMEDILM

SK2 SK4

RI R22212 I560A

LP16.5V0.065A

DITIL209

BIT9V

R3270kfl

SK5

HcHD2TIL209

TR1BCIOS

Fig. 1. Complete circuit diagram for the Visual Continuity Tester.

Showing how all components are mounted and interwired on the front panel.

CROCODILECLIP

FLAT

,R1

UNDERSIDE VIEWS

21 E 72

OR

2 OFF EACH REQUIRED

MI .1PLUGS

Fig. 2. Wiring details for the unit. Note the earth tagwhich is trapped under the front 3anel when this is fullyassembled. If a panel other than metal is used be sureto provide an ext-a wire from the emitter of TR1 to thenegative os the battery.


about 0-2 milliamps. The base cur-rent required to cause this collec-tor current to flow is 1.6 micro-

0-2mA)amps (-120

Therefore the maximum valueof the base resistor from Ohm's law

8.4VC1 6µA) =5-25 megohms. From

this we must subtract the fixedbase resistor of 270 kilohms to ob-tain the upper limit of the HIGHrange which is seen to be about 5megohms.

STARTHERE FOR

CONSTRUCTION

CONSTRUCTIONThe construction is quite

straightforward, all the details areshown in Fig. 2. Nothing is particu-larly critical about the layout, andcan be varied to suit the case used.

The only points to watch for arethe correct orientation of the 1.e.d.and the transistor.

Two test leads are made upusing 2mm plugs and test clips (orcrocodile clips). In the prototype,flexible multistranded leads wereused and found most convenient.

The completed Visual Continuity Tester prior to mounting in the case.

TESTING AND USEOnce constructed and the circuit

checked for any errors the batterycan be connected. It was notthought necessary to provide anon/off switch as the current drainis negligible.

In use the test leads are con-nected to the appropriate rangeand then clipped to the circuitunder test. For example, if theresistance of the circuit is unknownfirst try the MEDIUM range. If thereis no light then it can mean thatthe circuit is either open circuit orthe resistance is greater than 39kilohms.

Using the Visual Continuity Tester for checking resistancebetween two points on a printed circuit board.

Now try the HIGH range, if theresistance is not greater than5 megohms the 1.e.d. will light.

If when the MEDIUM range istried and the 1.e.d. lights up thismeans there is continuity but theresistance could be between nearzero and 39 kilohms. To find out inwhat range it could be, the Lowrange is used. This will then tellyou where the resistance of thecircuit lies. That is, between 0 and100 ohms or 100 ohms to 39kilohms.

The brilliance of bulbs and l.e.d.swill be seen easily if they areshielded from extraneous light. ti


P.C.B.'s and COMPONENTSfor E.E. PROJECTSPrices shown are for kits of on board mountedcomponents including potentiometers but excludinghardware and transformers. Send s.a.e. for fulldetails naming kit. All prices below include VAT.P & P 30p.

Components P.C.BRef. Kit P.C.B.

Jan MetronomeTouch SwitchCode ScramblerRapid Diode Check

Feb Car AlarmLead TesterChaser Light DisplayAC Meter Converter

Mar Audio TesterC.R. Substitution BoxCatch -a -lightWeird Sound

Apr Roof Rack AlarmMains Delay SwitchPocket Timer

01

02030405060708091011

121314

15

1 891.062.78

781.161.268 191.748.403.482.652.711.521.711.34 A

P.C.B.'s designed by TAMTRONIK toE.E. specified dimensions.

TAMTRONIK LTD. (DEPT. E.E.)217, Toll End Road, Tipton,West Midlands, DY4 OHW.Telephone: 021-557 9144

65*74*81*52*80*51

1 7560*

(2) 1 74*

82

62*60*94*60*

Buy it with Access

Be anELECTRONIC

ENGINEERDo something PRACTICAL about your futureFirms all over Britain are crying out for qualified people With

the right training, you could take your pick of these lobsNow, the British Institute of

Engineering Technology will train Courses inyou in your spare time to be an C & G Elect. TechniciansElectrical Engineer.

C & G Elect. InstallationsYou risk nothing ! We prom-

Telecomms. Technicians Examsise to get you through your Television Servicingchosen course -or, refund your Radio Maint. & Repairs (BIET)feel Pratt. Radio & Electronics

So, loin the thousands whoPlus over 60 otherhave built a new future through

home study courses.home study Engineering courses.

POST COUPON FOR FREE 44 PAGE GUIDE

BRITISH INSTITUTE OFENGINEERING TECHNOLOGY

Aldermaston Court, Dept. TEE 33

NAME (Block capitals please) -' ADDRESS

Reading RG7 4PF.

POSTCODE

AGE',Accredited by CACC of AeccMember

IM MN NI no E. IM

Everyday Electronics, June 1978

Other Subjects

CATALOGUE/CROW ronmSEND S A E

700+ Top quality components for the beginner and expertalike. Despatched by (1st Class for small packets)subject to availability. Discounts. 5% above L.S. and 10%above C20

741ONLY

0555

501551IP

T11.209ON15P

1N4001ONLY5p

Comporents below are a small sample from our range.Many more semiconductors available. Additionally we cansupply priced component lists for all E.E. projects from Oct77 onwards. Send SAE for up to fou. Let us quote you forany requirements-Export welcome.

Capacitcr, CasesElectron-

P Transistors TransistorsPolystyrene Min. Horiz.

Value (HP) MB2 6598; 10031-ep BC309 lip 2NI893 25p

BC308 lip 2N171I 24pAxial MBI

l/63V 10p M83 13p 2 2M S1BC327 1115 2N2219 29p2 2/63V 10pBC328 ISp 2N2369A 22p

(at I, 2-2+ BC337 15p 2N2646 92p4-7/63V 10p 4 7 decades) BC338 ISp 2N2905 llip10/63V lOpI0/25V Vero Cases BC44I 34p 2N2926G 1315

22125V 110p0p75 Series BC461 36p 2N29260 lip

47/25V 10p410 390p Min. Vert. Sp BC547 13p 2N3053 22p

100/63V 25p ' 411 430p 100.51.1 M SI BC548 13p 2N3054 73p412 555I00/25V 10p

(at I. 2-2 + BC549 14p 2N3055 65pp

220,125V 25p237 240p 4 7 decades) BC557 16p 2N3702 Ilp

470/63V 37p238 300p BC558 ISp 2N3703 11p239 350p BC559 15p 2N3704 Ilp

470/25V 34p1000/63V 46p

798 450p Transistors BCY70 20p 2N3705 IlpI000/25V 54p

AC126 20p BCY7I 20p 2N3706 Ilp1200/25V 85p

AC127 20p BCY72 16p 2N3771 210pAC128 27p BDII5 54p 2N3772 195p65 Series AC.I41 2Ip BD123 110p 2N3773 2.80p2514 180p AC142 2Ip B0124P 90p 2N3819 24p

5111015Tantalum 2 A-176 28p BD I 31 i68p 2N3866 97p

0-47/35V 14p25168 AC187 lip BDI32 70p 2N3904 Ilp

1.0/35V 14152520 260p2522 p ACI87/8MP

AC188 2Ip 80131/ 2N3906 12p2.2/35V 1615

340 2MP 140p 2N5457 42p4-7/35V 1715

2523 690p 53p BD133 SOp 2N5458 42p10/25V 2115 ACI87K 2Ip BDI35 41p 2N5459 43p22/16V 24p AC.188K 21p BDI36 39p47/6 3V 24p Vero Boards ADI49 79p BDI37 40p

0 I" AD161 75p BD I 38 4Sp Signal2 5" ,L. 3-73" AD162 75p B0139 42p Diodes

Polyester- SOp ADI6I/2 BD140 47p AAI 19 7pRadial 3 75" x 3-75" MP 160p BFI80 35p 0A47 9p

59p A:127 36p BF181 35p 0A90 7p0 001 7p 2.5".5" S9p A:139 48p BF194 13p 0A91 7p0 0022 7P 3.75" >. 5" 66p A:239 Slp 13F 195 13p 0A202 fp0 0047 7p0-01 7p BC107 13p BF196 13p 1N4148 4p

Dec & BlobBC108 13p 8F197 13p0.022 715 BC109 13p BFX84 24p

o-0477p

S. Dec 216p BCI26 20p BFX87 29p RectifiersBC140 35p BFX88 29p BY127 14p

0-47

.1 SpT. Dec 399p0-22 9pIllp BC142 30p BFYSO 23p N4001 Sp

1.0 lip2.2 36p Blob 0. I'

BC143 30p BFY5I 23p N4002 7pB' -I47 10p BFY52 23p N4004 7pBC 148 10p B5X20 lip N4005 Sp2.5"/5" 33p

2 5"/3.75" 2Sp BCI49 Ilp M)480 12.5p N5401 14p

3.75"/5" 50pBCI54 16p MJ481 I 55p N5404 16p

Polystyrene BCI57 12p MJ490 137p W04 31pValue (pF) BCIS8 lip MJ491 I73p10 P BC159 ISp M12501 246p22 6p LE DS BCI61 32,3 M13001 20Sp Zeners33 6p T1L209a 15p 131=167 12p MJE340 49p 400mW47 6p TIL209G 3Sp BC168 lip M15520 Slp 3 -3V -15V Ilp100 6p TIL209Y 3Sp BC169 12p MJE2955 ffp150 ap LEDO.2"R ISp BCI70 16p M153055 115p220 ap LED0-2"G 35p BC171 1 I p MPF102 40p Re ulators330 6p LE D0 2"Y 35p BC 172 13p 0C28 120p 780 15Sp470 6p DL707 iOOp BC173 14p 0C35 lip 7812 ISSp680 6p BC177 19p 0070 35p 7815 155p1000 ap BC178 19p 0071 I6p 723DIL 60p1500 ap I.C. SKTS BC179 19p 0081 35p

23230000

6p 14 PIN OIL BCI83L Ilp TIP32A 44p IX.,apBC182L Ilp TIP3I A 42p8 PIN OIL lip

4700 11p 24p BC184L lip T1P4IA S9p 741 30p10000 fp 16 PIN DIL BCI 86 25p TIP42A 59p 747 flip

27p BCI87 27p TIP2955 104p 748 SOpBC207 1 1p TIP3055 6Sp 555 SOp

Ceramics BC208 Ilp T1543 35p 556 99pSOV BC209 lip ZT X107 14p 4001 26p

(Pack 3) 10p Resistors rif22 (Packs of .)

BC2I2L lip ZTXI08 14p 4011 26pBC2I3L Ilp ZTX109 14p 7400 IS

33 6p BC2I4L Ilp ZTX300 17p 7402 Illp47 BC237 16p ZTX500 lip 7490 112p100 BC238 16p 2N697 lipISO Carbon Film BC239 16p 2N706 lip220 Son BC301 32p 2NI131 30p Switches270 I Z-10M.a. BC303 32p 2NI132 30p Slide DP lip330 512 Values BC307 Ilp 2N1613 24p Push MakelOp4705601000 All prices include VAT. P&P FREE over i2 20p2200 Name47000.01uF Adress0.022/sF0.047uF

Oct an ACE up woo slocuelACE AMILTBONIX ITO

OtetEE Tool Street

WalefelSW.Ukeire WFI5JR

519

The Extraordinar

Experi-ments

of

Proie55Ernes

Evemureby linthony John Bassett

"u ELLO there, Bob!" the Prof's" voice came from a small loud-

speaker concealed in a nearbyarmchair. "Caught you again; dosit down!"

"Oh peanuts!" Bob was frus-trated again, "Prof., I never domanage to spy on the secret experi-ments you carry out when there'sno-one else in the laboratory."

He sat in the armchair, whichwas one item of the Prof's collec-tion of experimental remote -con-trolled mobile furniture. With agentle whirr it lifted slighty tohover a few centimetres above thefloor then whisked Bob along thecorridor to arrive once again inthe presence of the Prof. in hislaboratory.

Bob knew there was a lot hecould learn from the Prof. andoften tried to get to know moreabout some of his most advancedexperiments.

But the Prof. wisely insisted thatBob should learn more of thebasics first.

VALVE AMPLIFIER"Prof., I was fascinated by your

use of transistors as interfacedevices between circuits whichoperate from different supply -voltage levels, and I have noticed

that recently some of my friendsare beginning to show a lot ofinterest in thermionic valves andvalve -operated equipment.

I would like to know a lot moreabout valves, but first I would liketo ask your advice on a specificproblem: can valves also be usedas interface devices in conjunctionwith transistors, in order tooperate at even higher voltages?One of my friends is in a smallband which uses a lot of electronicequipment and effects and he hasa Vox AC -30 amplifier.

Unfortunately the gain of theamplifier, which is an older modeland is his favourite, is too low togive adequate volume with his newguitar, so he uses a small transis-torised preamplifier. Occasionallythe battery in the preamplifier unitruns out at the most inconvenienttimes; usually at night, on stage inthe middle of a booking, his guitarsound fades and becomes dis-torted. He would like to have apreamplifier built into one of theinput -channels to provide gain,especially at high frequencies ashe also wants some treble -boost.

I seem to remember you men-tioning to me a circuit where oneof the valves acts as an element inthe power supply for a transistorpreamplifier, and at the same time

amplifies the output of the pre-amplifier further, and this savesthe expense and complication ofan extra mains power supply forthe preamplifier.

This sounds like a very interest-ing circuit and I wonder whetheryou could tell me about it so Icould use it in this amplifier?"

Suddenly Bob spotted, on anearby workbench, the old butcherished Vox AC -30 amplifierwhich belonged to his friend.

"What! How did that get here?"he exclaimed.

"Because you mentioned to yourfriend that you were coming toconsult me, Bob, and he decidedto call round and leave the ampli-fier at the laboratory. So now wecan not only discuss possible solu-tions to his problems, but also putthem to use for your friend! How-ever, he has mentioned that theamplifier has developed a faultwhich seems to be getting worse.At first there was a crackling andsome distortion when he playedloudly.

OUTPUT TRANSFORMERNow the distortion has become

worse, and commences at a muchlower volume, but only after hehas played a few notes, some of


15-240 Watts!HY5Preamplifier

HY3015 Wattsinto 80

HY5025 Wattsinto 80

HY 12060 Wattsinto 8

HY200120 Wattsinto 8u

HY400240 Wattsinto 40

POWERSUPPLIES

The HY5 is a mono hybrid amplifier Ideally suited for all applications All common inzntfunctions (mag Cartridge, tuner, etc) are cat. ed for internally. The desired function is achissieither by a multi -way switch or direct connection to the appropriate pins. Th internal volumeand tone circuits merely require connecting t external potentiometers (no: included). The HYSis compatible with all I.L.P. power amplifies and power supplies. To ease construction andmounting a P.C. connector is supplied with each pre -amplifier.FEATURES: Complete pre -amplifier in single pack-Multi-function equalization-Low noise-Low distortion-High overload-Two simply combined for stereo.APPLICATIONS: 111-FI-Misers-Disco-ludar and Organ-Public addressS PECIFICATIONS:INPUTS. Magnetic Pick-up 3mV; Ceramic Plck-up 30mV: Tuner 10OrriV Microphone lOrriV:Auxiliary 3-100mV; Input impedance 4 7k0 it 1kHz.OUTPUTS. Tape 100mV; Main output 500m% R.M.S.ACTIVE TONE CONTROLS. Treble* 12015 at 1004z; Bess j at 100Hz.DISTORTION. 0 1% at 1kHz. Signal/Noise Patio aide.OVERLOAD. 38d5 on Magnetic Pick-up. SUPPLY VOLTAGE * 111-50V.Price LI' 22 + Up VAT PAP free.

The HY30 is an exciting New kit from I.L.P. It features a virtually indestructible I.C. with shodcircuit and thermal protection. The kit consists of I.C., heatsink, P.C. board. 4 resistors, 5capacitors, mounting kit, together with easy to follow construction and operating instructions.This amplifier Is ideally suited to the beginner in audio who wishes to use the most up -to -datatechnology available.FEATURES: Complete K11 --Low Distortion-Short, Open and Thermal Protection-Easy toBuild.APPLICATIONS: Updating audio eoulprrent-Guitar practice amplifier-Test amplifier-audio oscillator.S PECIFICATIONS:OUTPUT POWER 15W R.M.S. into SO: DISTORTION 0 1% at 1-5W.INPUT SENSITIVITY 500mV. FREQUENCY RESPONSE 10141-18kHz-3d15.SUPPLY VOLTAGE ± 1BV.Price Li 22 + Sip VAT P&P free.The HYSO leads l.L.P.'s total integration approach to power amplifier design. The amplifierfoetus, an Integral heatsink together with the simplicity of no external components. During thePast three years the amplifier has been refined to the extent that it must be one of the moatreliable end robust High Fidelity modules In the World.FEATURES: Low Distortion-Integral Heateink-Only fine connections -7 amp output tran-sistors-No sternal componentsAPPLICATIONS: Medium Power HI -Fl systems-Low power disco-Q.1Sr amplifierSPECIFICATIONS: INPUT SENSITIVITY 500rnVOUTPUT POWER 25W RMS into 50 LOAD IMPEDANCE 4-1110 DISTORTION 0.04% at 25Wat WUSIGNAL/NOISE RATIO 75011 FREQUENCY RESPONSE 10H1 -45k141 -3d11.SUPPLY VOLTAGE ± 25V SIZE 105 50 25mmPrice L5 U + sip VAT P&P friarThe HY120 is the baby of I.L.P.'s new high power range. Designed to meet the most 'nettingrequirements Including load line and thermal protection this'amplifier ars a new standard Inmodular design.FEATURES: Very low distortion-integral hsatsInk-Load line protection-Thermal protec-tion-Five connections-No external componentsAPPLICATIONS: HI-FI-High quality discc-Public address-Monitor amplifier-Goiter andorganSPECIFICATIONSINPUT SENSITIVITY 500mV.OUTPUT POWER 80W RMS into BO LOAD IMPEDANCE 4-100 DISTORTION 0.04% at 00Wat 1kHzSIGNAL/NOISE RATIO POde FREQUENCY RESPONSE 10111-45kHz- 3d5 SUPPLY VOLTAGE*35VSIZE 114 50 85mmPrise 415 W + 41 ft VAT PAP free.The HYPO° now Improved to gins an output of 120 Watts has been designed to stand the mostrugged conditions such as disco or group while still retaining true Hldl performance.FEATURES: Thermal shutdown-Very low distortion-Load line protection-Integral heatsink-No external componentsAPPLICATIONS: Hi-Fi-Disco-Monitor-Power slave-Industrial-Public AddressS PECIFICATIONSINPUT SENSITIVITY 500mVOUTPUT POWER 120W RMS into 80 LOAD IMPEDANCE 4 -ISO DISTORTION 0 05% at 100We t

SIGNAL/NOISE RATIO MS FREQUENCY RESPONSE 101.41-411kHz- 3411 SUPPLY VOLTAGE*45VSIZE 114 50 85mmPrice L23. 32 + h 87 VAT PAP free.The HY400 is I.L.P.'s "Big Daddy" of the range producing 240W into 401 It has bean designedfor high power disco address applications. It the amplifier is to be used at continuous highpower levels a cooling fan is recommended. The amplifier includes all the qualities of the restof the family to lead the market as a true high power hi -fidelity power module.FEATURES: Thermal shutdown-Very low distortion-Load line protection-No externalcomponents.APPLICATIONS: Public address-Disco-Power slays-industrialSPECIFICATIONSOUTPUT POWER 240W RMS Into 40 LOAD IMPEDANCE 4-150 DISTORTION 0 1% at 240Wat 1kHzSIGNAL NOISE RATIO 5445 FREQUENCY RESPONSE IOW -MHz- 3011 SUPPLY VOLTAGE*45VINPUT SENSITIVITY 50ZunV SIZE 114 100 85mmPrice EU 17 + L2 57 VAT PAP free.

PSU36 suitable for two HY30's 13 22 plus Sip VAT. P/P freePS1.150 suitable for two HY50's G 82 plus lip VAT. P/P Ira,.PSU70 suitable for two HY120's 113 75 plus 11 II VAT. PiP free.PSUIO suitable for one HY200 412 if plus It 91 VAT. P/P free.PSU180 E23 IS + Et 85 VAT.B1 La 411 +G N VAT.

Aik640*44

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MULTIMITIER BARGAINSA special bulk purchase of EagleMultimeters enables us to offer twofrom their range at up to 15% offEagle's own recommended retail price.

EP2OKN20,000 opv multimeterwith anti -parallaxmirror, 'off' dampingDC volts: 0 to 0.25,5, 25, 125, 500, 1,000(20,000 opv). ACvolts: 0 to 10, 50, 250,1,000 (10,000 opv).DC 0 to 50uA, 2.5 mA, 250 mA.Resistance: 0 to 60K,600K. 6 Meg. Deci-bels: -20 to +22 dB. Dimensions:118 x 86 x 34 mm.PRICE L16.16+ 8% VAT.

POWER SUPPLY UNITTYPE PP1'

Switched 3, 44, 6, 7}, 9 and 12 volts at500mA. With on/off switch and pilotlight.Size: 130mm x 55mm x 75mm approx.OUR PRICE:Only 6600 8% VAT

C1095 20,000 opv multimeter withhinged 4 -position scale for easy -readingbench use. Anti -parallax mirror, 3 -

colour scale, overload protection.Ranges: DC volts: 5, 25. 50, 250, 500,2,500 (20,000 opv). AC volts: 10, 50,100, 500, 1,000 (10,000 opv). DC

50 uA, 2.5 mA, 250 mA.Resistance: SO K, 5 meg. Decibels:-20 to +22 dB. Dimensions: 140 x85 x 35 mm.PRICE: 114.31 -- 8% VAT

ABS PLASTIC BOXESHandy boxes for construction projects.Moulded extrusion rails for P.C. orchassis panels.Fitted with I mm Front Panels.1005 = 105 x 73 x 45mm = Up1006 = 150 x 74 x 47mm = 11.051022 = 107 r 85 45mm = 80p(sloping front) Plus 8% VAT.

POPULAR DUALIMPEDANCE

MICROPHONEUni-Directional Car-dioid Dynamic Micro-phone. Type No. UD130.Freq. Response: 80-14,000 Hz.Impedance: Dual -

600 ohm or50k ohm.

On -off Slide Switch.Supplied with Mic. Holder (I^ thread)and approx. 17ft of cable with micro-phone connector and lack plug attached.PRICE: 110.00 + 12}% VAT.

BARGAIN PROJECT BOXA Plastic Box with moulded extrusionrails for P.C. or chassis panels withmetal front plate fitted with fourscrews (all supplied).Size: (internal): 81 x 51 x 28mm.PRICE: 60p + 8% VAT.

FERRIC CHLORIDEAnhydrous Ferric Chloride in doublesealed one pound 'Polypaks'.PRICE: LI -15 per lb + 8% VAT.

'BARGAIN TRANSFORMER'240v PRIMARY 12-0-12v, 300m/ASEC. Approx. size: 60 x 40 x 50mm.Fixing centres: 75mm.

PRICE: 11.80 -- 8% VAT.

ACCESS AND BARCLAYCARD ACCEPTED-PHONE ORDERS WELCOMED.ALL PRICES INCLUDE POSTAGE-PLEASE ADD VAT AS SHOWN-S.A.E. WITH ALL ENQUIRIES PLEASE.Personal Callers Welcome at: 21 Green Lanes, Palmers Green London, N.13.Phone: 88R-3206 and 13 SOUTH MALL, EDMONTON, N.9. Phone: 803-1685.

ANNEDUNCIN4GA NEW SETelf UAWlEILECTIND%11CSThis 5 volume set contains over 500 pages.Bound in stiff linen. Cover size 8%in x 5in.Price f7.50 per set (we pay the postage).

Book 1. Introducing Electronics Book 4. Meters/Voltage-dividersBook 2. Resistors/Capacitors Book 5. Transistor Project CircuitryBook 3. Inductors/DiodesThe manuals are unquestionaby the finest and most up-to-date availableand represent exceptional value.This series has been written in a fascinating, absorbing and excitingway, providing ar approach to acquiring knowledge that is a veryenjoyable experience. Suitable for industrial trainees, City and Guildsstudents, DIY enthusiasts and readers of electronic journals.Each part explains electronics in an easy -to -follow way, and containsnumerous diagrams and half tone blocks with construction details andcircuit diagrams for making the following transistor projects: LampFlasher, Metronome, Wailer, Photographic/Monostable Timer, MetalLocator, Geiger Counter, Radio Receiver, Intercom., Intruder Alarm,Electronic Organ, Battery Eliminator, Anemometer, Sound Switch,Light and Water-ooerated Switches, Pressure -operated Switches, Lightmeter, Radio Thermometer, Ice Alarm,

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which are loud, and clear of thedistortion which he complains of.This leads me to suspect that thefault may be in the primary of theoutput transformer, although in-termittent faults with cracklingand distortion can easily occurelsewhere in the circuit due tovibration from the loudspeakersand from the frequent transportwhich these amplifiers are usuallysubject to."

"Why do you suspect the outputtransformer, Prof?"

"Because this component is sub-ject to particularly high voltagesurges when a loud note is played,especially if the input is a squarewave. Then the inductance of theprimary winding causes voltagespikes at the leading and trailingedges of the square -wave.

INSULATION BREAKDOWNThese high voltages sometimes

result in a breakdown of the insu-lation between adjacent windingsor between nearby turns of thesame winding, and I think that thismay be the problem with thisamplifier. When the insulationbreaks down between adjacentturns of the same winding, a par-tially conducting track of carbonforms between the nearby turns.This absorbs power when theplayer strums loudly, but muchless when he plays quietly, as thereis then very little induced voltagebetween the turns.

When he plays loudly, the powerabsorbed by the conducting carbontrack causes it to raise in tempera-ture. This produces more carbonfrom nearby insulating materialand the fault worsens, until, as Isuspect in this case, more power isabsorbed in the carbon than isdelivered to the loudspeakers.

This results in a low -volume, dis-torted output from the amplifier,and if he continues to try to playloudly, the rise in temperaturewithin the transformer may causeit to produce smoke and fail morecatastrophically.

VALVE BASESAnother component where car-

bon tracks can be formed withsimilar results is the valve base inwhich each output valve is held.Each of the output -valve bases issubject, along with the valve itself,to the same high -voltage spikesproduced by the output trans-former, and a track of hot carbonis formed, spreading until it mayreach a point of low potential andcause the valve base to catch fire.

"What I usually recommend insuch cases is replacement of theplastic valve -bases with ceramicones. Although these are more ex-pensive and may have to beordered specially, it is impossiblefor them to carbonise, and so it isworth the trouble of obtainingthem."

The Prof. finished unscrewingthe back of the amplifier. He slidit out of its cabinet and fitted anextension to the loudspeaker ter-minals, as he knew that it is, forthe most part, unwise to operatea valve audio power amplifierwithout a proper load on thespeaker terminals. He then re-moved the base of the amplifierto reveal the connections to theprimary of the output transformer.

NEON TEST"Now," he told Bob, "I am going

to show you a simple test whichwill often reveal the presence ofshorted turns in an audio outputtransformer of a valve amplifier.Here is a neon indicator lamp withsymmetrical electrodes, and it isalso fitted with a 270 kilohm serieslimiting resistor."

Bob could see the small neonbulb contained two parallel wireelectrodes. The Prof. soldered the

leads of the neon indicator, to-gether with its 270 kilohm limitingseries resistor, to the opposite endsof the primary winding of the out-put transformer. Then he pluggedthe amplifier into the mains supplyand switched on. Plugging the out-put of an audio signal generatorinto one of the inputs, he told Bob:

"When I turn the volume up,both electrodes of the neon shouldglow with equal intensity if thetransformer is satisfactory and thesignal I am injecting is symmetri-cal."

However, even at maximumvolume the sound from thespeakers was very weak and dis-torted, and neither electrode ofthe neon lamp glowed.

SHORTED TURNS"It seems to me that we have

here a very severe example ofshorted turns in the output trans-former. Usually even if it is faulty,at least one electrode of the neonwill light as the fault usuallyoccurs in one half of the primaryof a push-pull transformer, anddespite the damping effects of this,the other half will usually producesufficient voltage surge to light oneelectrode of the neon."

The Prof. switched off the ampli-fier and unplugged it from themains supply socket. Then he useda multimeter to ensure that thehigh voltage from the h.t. supplyhad drained away, before workingon it. He removed the faulty trans-former and, with a few instruc-tions in a strange robotic language,handed it to his experimentalrobotic assistant.

"Now whilst the Robot rewindsthis transformer using new copperwire and insulation I will draw thecircuit diagram of the output, andwill discuss what went wrong andhow to prevent it, as rewinding orreplacement of these transformerscan sometimes be expensive, notto mention the embarrassment ofhaving equipment fail before anaudience. This, incidentally, is arare occurrence with the Vox AC -30, which is a very popular ampli-fier and this one probably failedfrom sheer old age and very heavyuse!"

Deftly the Prof. began to drawout the circuit diagram of the four -valve output stages of the ampli-fier.

To be continued


THE DYNAMIC DUO

The C15/15 is a unique Power Amplifier providingStereo 15 watts per channel or 30 watts Mono andcan be used with any car radio/tape unit. It is simplywired in series with the existing speaking leads and inconjunction with our speakers S15 produces asystem of incredible performance.

A novel feature is that the amplifier is automaticallyswitched on or off by sensing the power line of theradio/tape unit, hence alleviating the need for anon/off switch.The amplifier is sealed into an integral heatsink and isterminated by screw connectors making installation avery easy process.

The S15 has been specially designed for car use andproduces performance equal to domestic speakersyet retaining high power handling and compact size.

C15/1515 watts per channel into 412Distortion 0.2% at 1 kHz at 15 wattsFrequency Response 50Hz-30kHzInput Impedance 813 nominalInput Sensitivity 2 volts R.M.S. for 15 watts outputPower Line 10-18 voltsOpen and Short Circuit ProtectionThermal ProtectionSize 4 x 4 x 1 inchesC15/15 Price L17.74+£2-21 VAT P&P free

Data on S156" Diameter51" Air Suspension2" Active Tweeter20oz Ceramic Magnet15 watts R.M.S. Handling50Hz-15kHz Frequency Response40 ImpedanceS15 Price per pair L17.74-1-£2.21 VAT P&P free

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Crossland House,NackIngton,Canterbury. KentTel 01227) 83218

EL ECTRO ALUEAll the many types of components we supply are BRAND NEW andguaranteed and only from manufacturers direct or approved suppliers.

(No surplus, no seconds)CMOS-buffered and protected (BE)4000 239 4013 519 4023 13p 4043 1 004001 23p 4014 1.04 ' 4024 I 04 4044 94p4002 23p 4015 1.14 4025 23p 4046 1.404006 1-14 4016 Slp 4026 I 75 4049 54p4007 13p 4017 114 4027 60p 4050 53p4008 99p 4018 1.32 4028 9Sp 4060 1.404009 62p 4019 62p 1 4029 1 13 4069 30p4010 63p 4020 1 32 4030 51p 4070 50p4011 23p 4021 I 14 4041 64p 4071 16p4012 239 4022 113 4042 96p 4072 26p

4081 1394082 26p4510 1.424511 1.504514 3.304516 1.444518 1.264520 I 264543 1-304583 1.45

OUR COMPUTER TAKES GOOD CARE OF VOUR ORDERSSIEMENS CAPACITORS World-famous for quality and depend-ability -exceptionally large stocks held.PCB TYPES-7.5mm PCM 0.001 to0.01 Sp each: 0.015 to 0 -047 6p each:0 068, 0.1 7p each.CERAMIC - 2.5mm PCM 0.01,0022 4p: 0-033. 0047 Sp each:0.068 6p each: 0 17p.ELECTROLYTICS--1/100, 10/25,10/63, 100/25, etc. etc.For full range see our current lists.

RESISTORS1, }, } watts 2p each: metal film,metal oxide and I watt carbon Sp each: Good quantity discounts. Magneticfield dependent from L1 .S0. Halleffect from L1.23.

SIEMENS TRANSISTORSSilicon npn and pop from 8p each:LEDs, red 19p: yellow or green 23p(3 or 5mm): Photo transistors from76p.

KEEN PRICES GOOD SERVICE WIDE RANGESDISCOUNTS5% if list value of order over LIO10% if list value of order over L25-where cash (P.O. or cheque) is sentwith order.

V.A.T.-Add 8% to value of orderor 124% with items marked.(No V.A.T. on overseas orders).Goods sent post free on C.W.O.orders

in U.K. over a list value. Ifunder, add 27p per order.

MONTHLY BARGAIN LISTS S.A.E. brings monthly list of bargains.Also current quick reference price list of all ranges.Cash with order (P.O. or cheque payable to Electrovalue Ltd) or your

Access or Barclaycard number.TRADE AND INDUSTRIAL ENQUIRIES INVITED

For all round sat,sfact,on-be safe-buy it from ELECTROVALUE

ELECTRO ALOE LTDDept E.E.7,24 St. Judes Rd, Englefield Green, Egham, Surrey TW20 OHS.Phone Egham 3603. Telex 264475.Northern Branch (Personal shoppers only), 680 Burnage Lane, Burnage,Manchester MI9 I NA. Phone (061) 432 4945

Fit anew tape head

and transform theperformance of

your taperecorder

QUALITYREEL TO REEL

AND CASSETTE TAPE HEADS

Please enclose

Full Catalogue 25p 20p P&P with order

B24 -RP stereo cassette glass/ferrite record/playback E9.84812-01 mono cam. playbk. E1.60 824-Q1 stereo eau. playbk. E2.80

A28-05 stereo 8th cartridge E1.80 E 12 -09 stereo/mono cass. erase £1.80

5/7 Church St, Crewkerne, Som. Tel. (0460) 74321

£1995X A.T.El 60

Sok our communication problemswith this 4 -station Translator Intercomsystem 11 master and 3 Subs). In robustplastic cabinets for desk or wall mount-ing. Call/talk/listen from Mader toSubs and Subs to Master. Ideallysuitable for Swine'''. Surgery. Schools.Hospitals and Office. Operates on one 9%'battery. On/off switch. Volume control.Complete with 3 connecting wires each6611. A Battery and other acceuories.Adaptable for mains. Battery eft-Mator 14116 (optional) P & P. 99p.

Latest transistorised Telephone AmpMier with detached plug-in speaker.Placing the receiver on to the cradleactivates a switch for immediate two -stay conversion without holding thehandset. Many people can Men at atime increase efficiency in office shop.workshop. Perfect for "conference"calls: leaves the user'. hand. Tree tomake notes. consult Alec No long

ONLY waiting. saves time with longdielance

£1595 calls. On/off ...Bch, tolunie control.conversation recording model at

V.A.T. 11:211 Ill 96 VAT El 52. P. A P. 99p.y price refund guarantee on all

WEST LONDON DIRECT10-daSUPPLIES (EEC 169 1:11181110208items.RION "ream. LONDON. Wt01-937 6548

524 Everyday Electronics. June 1978

ROOM THERMOSTATFamous Satchwell, elegant design, intended towall mounting. Will switch up to 20 amps at main -voltage, covers the range 0.30 C. Special snip th,month E3 H.ROD THERMOSTAT -L3 -N,WINDSCREENWIPER CONTROLVary speed of your wiper to suitconditions. All parts and instruc-tions to make E3.76.

MICRO SWITCH BARGAINSRated at 5 amps 250V, ideal to make aswitch panel for a calculator and for dozensof other applications. Parcel of 10 (twotom-, Et.

RADIO STETHOSCOPEEasiest way to fault find, tracts signalfrom aerial to speaker when sierral stopsyou've found the fault. Use It cn Radio.TV, amplifier, anything. Kit comprisestransistors and parts includ-no probelobe. twin stethoset. 13 Si.

MULTISPEED MOTORSSix speeds are available 500, 850 and 1,000r.p.m. ano 7,000, 9.000 and 11,000 r.p.m. Shaftis I in diameter and approximately 1 in. long.230/240V. Its speed may be further controlledwith the use of our Thyristor controller. Verypowerful and useful motor size approx. 2 India. e S in. long. Price 12.

I2V MINIATURE RELAYdc operated wale IvV0

sets of change over contacts. The unique lesson ofthis relay is its heavy lead out wires: these provideadequate support and therefore the relay needs noflung: on the other hand there is a fixing bolt protrudingthrough one side so it you wish you can fix the relayand use its very strong lead outs to secure circui com-ponents -an expensive relay; but we are offerien it toronly 17p each. Don't miss this exceptional barpein!

EXTRACTOR FANEx computers -made by Woodsof Colchester, ideal for fixingthrough panel -reasonably quietrunning -very powerful 2500rpm. Choice of two sizes 5" ortir die Ea 43.

MAINS RELAYSWith triple 10 amp changeover Contacts -operating coil wound for 230V a.c. Chassismounting one screw fixing, Pi ice

f f2S

MICRO AMPLIFIEREx behind the ear hearingSi complete with volumecontrol. 12 N. Case notsupnlinn

MERCURY BATTERIESBank of 7 Mercury cells type 625 : "41,which are approx. tin diameter ' areaby thick in plastic tubegiving a total of 10.7V.Being in a plastic tube it Is very easy tobreak up the battery Into separate cellsand use these for radio control andsimilar equipment. Carton of 25 batteriesE1 N.

PP3/PP9 REPLACEMENTJapanese made in plastic container withleads size tin. 1/in. 1/In., this is ideal topower a calculator or radio, it has a full waverectifier and smoothed output of 9V suitablefor loading of up to 100mA. E2 53.

SWITCH TRIGGER MATSSo thin is undetectable under carpet but willswitch on with slightest pressure. For burglaralarms, shop doors, etc 241n. 18in. £2.55.13in 10.n Et .95.

MAINS TRANSISTOR PACKDesigned to operate transistor sets and amplifiers. At....siableoutput 8V. EV. 12V for up to 500mA (class D working) Takesthe place of any of the following batteries: PP1, PP3 PP4,PP6, PP7, PP9 and others Kit comprises: main transformerrectifier, smoothing and load resistor condensers end In-structions Real snip at only E2.1141.

CONTROLDRILL

SPEEDS

DRILL CONTROLLERElectronically changes Wes trout ap-proximately 10 revs to maximum. Fullpower at all speeds by fingertip controt. Kit Includes all parts, case every-thing and full Instructions 13.45.Made-up model /1 extra

8 POWERFULBATTERY MOTORSFor models, Meccanos, drills, remote controlplanes, boats, etc. Lt.

ROTARY PUMPSelf Priming. portable, fits drill or elec-tric motor, pumps up to 200 gallons perhour depending upon revs. Virtuallyuncorrodablii, use to such water. oil.petrol, fertiliser. chemicals. anythingliquid. Hose connectors each end. 12.

SHORTWAVE CRYSTAL SETAlthough this uses no battery it givesreally amazing results. You will re-ceive an amazing assortment ofstations over the 19. 25, 29, 31 metrebands. Kit contains chassis frontoanel and all the parts Et 94 -crystalearphone 51p including VAT andoostage.

MULLARD UNILEXA mains operated 4 + 4stereo system. Rated oneof the finest per`ormers in 'E. ,11.the stereo field this wouldmake a wonderful gift for almostanyone In easy-to...Nimblemodular form and completewith a pair of Plessey speakersthis should sell at about EN -but due to a special bulk buyand as an intent ye for you to buy this montn we offer thesystem complete at only E15 MI including VAT and postage.

HUMIDITY SWITCHAmerican made by Ranco, their type NoJ11 The action of this device dependsupon the dampness causing a membraneto stretch and trigger a sensitive micro -switch adjustable by a screw, quitesensitive -breathing on it for instancewill switch it on. Micro 3 amp at 250V a.c.Overall size of the device approx. 3E1n.long. 1 in. wide and 111n. deep. 75P.

DELAY SWITCHMains operated -delay :an be accu-rately set with pointers knob for periodsof up to 2/ hrs 2 contacts suitable toswitch 10 amps -second contact opensfew minutes after 1st contact Pip.

25A ELECTRIC PROGRAMMERLearn in your sleep. Have radio playing and kettle boilingas you wake -switch on lights to ward off intruders -have

a warm house to come home to.All these and many other thingsyou can do if you invest in anelectrical programmer Clock byfamous maker with 15 amp on/offswitch. Switch -on lime can beset anywhere to stay on up to 6hours independent 6C minute mem-ory jogger. A beautiful unit.

MULLARD AUDIO AMPLIFIERSAll in module form, each ready built complete with heatsinks and connection tags. data supplied Model 1153 500m W.

power. output Et II8Model 1172-10 watts powe output E3Model 1172 1W. Dower output E2 25Model EP9000 4 watt power output E2 NEP 9001 twin channel or vireo pre -ampE2

PRINTED CIRCUIT KIT PROJECTSCONTENTS (1) 2 CopperLaminate Boards 411n. 24in(2) I Board for Matchbox Radio.(3) 1 Board for Wristwatchr Radio, etc. (4) Resist (5)Resist Solvent (6) Etchant. (7)Cleanser/Deg r (8) 18 -page Booklet Printed Circuitsfor Amateurs (1) 2 MiniatureRadio Dials SW/MW/LW.Also free with each kit (10)Essential Design Data Cir-cuits. Chassis Plans, etc forPROJECTS. Et MI.

SOUND TO LIGHT UNITAdd colour or white light to your amplifierWill operate 1, 2 or 3 lamps (maximum450W). Unit in box all ready to work. DM.

MINI -MULTI TESTERAmazing, deluxe pocket size pre-cision moving coil instrument--tee/oiled bearings -1000 090 -mir-rored scale11 Instant ranges maalli.re:-DC volts 10. 50, 250, 1000AC volts 10, 50. 250. 1000DC amps 0-1 mA and 0-100 mAContinuity and resistance 0-150Kohms.Complete with insulated probes,+ads, battery, circuit diagram andinstructions.

Unbelievable value only ES NO + SOP POst and insurance.FREE Amps ranges kit enable you to read DC current from0-10 amps, directly on the 0-10 scale. It's free if you purchasequickly but if you already own mini tester and would like onesend E1 50p.

TERMS: Cash with order -but orders under 16 must add 50Pto offset packing etc.BULK ENQUIRIES INVITED. PHONE: 01-8881833

).BULL (ELECTRICAL) LTD(Dept. EE), 103 TAMWORTH RD.

CROYDON CR9 ISO

IT'S FREEOur monthly Advance Advertising Bargains List givesdetails of bargains arriving or lust arrived -often bargainswhich sell Out before our advertisement can appear -it'san interesting list and it's free -lust send S.A.E. Beloware a few of the Bargains still available from previoustines.

MAINS TRANSFORMERSAll these have 230 24av Mhz PrimaryVOLTAGE CURRENT REF.

2 amp TM 14v 5 amp TM 2

7 amp TM 321 amp TMI amp TM 37200 mA TM 21100 mA TM 21750 mA TM 7100 mA TM 332 amp TM 41 amp TM 12

amp TM 121 amp TM 51 amp 'c' core TM 63) amp TM 115 amp TM 3825 amp TM 15121 amp TM 154 amp TM 27I amp TM 9

amp TM 71 amp TM 1050mA TM 191 amp TM 412 amp TM 117 amp TM 273/ amp TM 273) amp TM 35

amp TM 12amp TM 13amp TM 14

5 amp TM 2712/ amp TM 156 amp TM 15100 mA TM 211) amp TM 162 amp TM 172 amp TM394 amp TIN 4011 amp TM 182 amp TM393/ amp TM 278 arnp TM 1537 amps TM 34

TM 15TM 22TM 29TM 24TM 23TM 24TM 24TM 25TM 25 L702TM 28 E3 71TM 25 ET etTM 36 L371TM 36 E3 78TM 36 L376

to

Sv5vSv-0-6 Sr5v-0-8 5.3v-0-6 3.3vSy

Sy + 8 5- sep winding

Dv10v10v -0-10v12v -0-12v12r13v12v12v -0-12v12v -0-12v15e tapped By15e15v -0-15v15v -0-15v17v18v20v20v20v20v -0-20v13v24v24v24v + 2v 7 amp24v25v26v30v tapped 24, 20. 15 6 1230v37u40v tapped 30v, 20v .1 10v 6 amp50v-2 amp korth 6 3v shrouded50v 8 amp80v 5 amp75e-3 amp with 6 3v shrouded75v 4) amp80v tapped 60v el 75v 4 amp100v 1 amp100v -0-100v

I

amp130. tapped 120v amp200v amp250v -0-250v with 8 3v 2A 50 mA250v 100 mA500v 50inA

PRICEEt NL1 62E275Se $5Le 65El 62L1 62E2 1$/1 62E1 MEt 62Et 52Et S2L1 81L279E3 24E4 81E414 12Ell 05E2 11111 IliEt 6213 24E2 78E4 22E4 3214 36E1 62El 90E1 62E4 32E4 86Li 8611 62E2 12E2 70E2 117E3 1$E2 43E2 NE4 32E4

131 HE4 N14 MI

C11 OSE752ES 10E7 62E7 12ET 02

Add 25% tc transformer prices to cover postage etc.3611mA E VOLTS MAINS UNITIdeal for power 6 volt equipment, cassettes. tape recorder oramplifier or other appliances requiring more than the averagemount of current. This is a really well made unit in plasticcase made for Crown Radio intended originally to clip IntoPollution. this has external battery type contacts but it Is aSimple matter to solder leads straight on to these contactsend this unit employs full wave rectification and is recom-mended in every wa, Price LI M.CALCULATORSBy famous makers like Texas. intended originally to be soldat quite high prices new and unused. Type 1. Basic functions-add. subt act, multiply, divide etc. Price ES 15. Type 2. -again basic functions but with rechargeable nicad batteriesPrice El *N. Battery sharpers for same a 71. Type 3 -basic functions but with memory and rechargeable batteries,

AM/FM RADelL11Sep IO+ 134o

Complete chassis, has turning scale with pointer volumecontrol. on off etc. Controls have edgewise knobs Theseradios can be mounted on or lust inside extension speaker.then you have a first class "music while you work" receiver.Reception on both AM -FM is better than average and evenin where FM is notoriously bad. good results have beenobtained. The output also is above average. the speakerpower is probably around I/ -2 watts. They can be poweredby fly batteries or 6v power supply, in fact the Crown RadioOne menticn above is ideal. would no doubt function asan AM,FM Tuner -real bargain i E5 SS + 810.UV TUBES (PHILLIPS ATINIC)Useful for bringing out water marks in stamps and specialcolours In rocks, similar specimens. We have these In twosizes 9" gsv once Et N + 12p. Post 50p + 4p 2ft 20 wigE2 N + 18c. post 75o + 8P1 POLE 1111 WAY SWITCHFor digital displays the 10 positions being evenly spacedthrough the 340 turn, and there is no stop. Silver platedcontacts art rated u 5 amps. normally an expensive switchbut offered Np each.TERMINALSVery good quality. British made. screw down type. topaccepts a 4mm plug The screw down section also has ahole through which solid wire may be passed, withinsulators for metal panel mounting, S popular colours.Price 111p each, Ref TS1. or 10 In a bag for Et 311. Ref. TSI/10.SKELETON PRE-SETMiniature size 2 2k, 10 for 11 N + 12/p.RELAY SASE14 pin standard for many plug in relays Hp + 4p.SPRING TRIGGER TERMINALSRed and black terminals mounted on insulated panel,approximate size 21" r These terminals grip like a vicebut connection in the fl,st place is quick and simple Holdback the trigger -push in wire -let go of trigger, definitely atime

Lsaver. Price Np the pair

VOLTAGE REF. PRICE260v

CURRENT

85; Kt(K5v:K

ifQuantity prices available. Please. unless you are calling.add 25% to your order to corer the cost of carriage. Alsoyou want to Collect, telephone the day before

SmA10mA

1M 301 M 31

TM 44TM 44

Plea! t 2a4pply

Lte 21117 92

80mA TM 26


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RADIO BOOK SERVICEWORLD RADIO TV HANDBOOK 1975 Editton CB 25

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to Had Tont Hen Hoe: A Treesese Lwow, IF O IlayeI (0-14Heat al Korot ..... mon nI Cob., TV, IC FSFun 47Ga.... oak war Eltotreeste Calaulator 'OwlHo. !to louold SY.01 Wave Rfteteo. le A renal,.

COSS

COeeAnnn4a .IckIes Lon. 0I6....G Cares/ [Cis

Se..6.na Trenstetas Rad. Recemstra (0-HSet, 'toe SAtot Wove Cele:seas Int INH.Ha. (1-01PRICES INCLUDE POSTAGE a PACKING.. S.A.E. FOR FULL LIST

4 CNILCNESTER 1011/11,WICK 1117111ECKENNAII KENT 11321111

SIMPLIFIED TV REPAIRS. Full repairInstructions individual British sets £4.50,request free circuit diagram. Stamp bringsdetails unique TV publications. Ausee, 76Church Street, Larkhall, Lanarkshire.

For SaleFOR QUICK SALE, quantity of 5in C.R.T.5UP1. As used in the Heathkit 10-18 Oscillo-scope at £25 each (includes VAT, postageand packing). Brand new, in manufacturer'soriginal boxes. Send Cash with Order to:HEATH (GLOUCESTER) LTD, Bristol Road,Gloucester.

LOGIC PROBE, suita'de TTL/CMOS 5-15Vindicates Logic States and Trigger Pulses.£12 inc. C. MARSHALL, 22 Oakfteld Road,Croyden, Surrey, CR0 2UA.

NEW BACK ISSUES of "EVERYDAYELECTRONICS". Available 60p each PostFree, oven PO 'Cheque returned if not instock. BELL'S TELEVISION SERVICES 190Kings Road, 11.irrogate, Yorkshire. Tel:(0423) 55885.

TRANSISTORS, Thyristors, Diodes, Led,Zeners, Voltage Regulators, Tracs, BridgeRectifieis, Plugs, So( kets ALL NEW. CheapE.G. 2N377.1 -2 15p, BEY% 95p, BD 131 45p.SAE list. JAI Electronics 39 Balvernie Gro,London SW111 SRR.

SMALL ADSThe prepaid rate for classified advertisementsis 16 pence per word (minimum 12 words), boxnumber 60p extra. Semi -display setting L400per single column centimetre. All cheques,postal orders, etc., to be made payable toEveryday Electronics and crossed "Lloyds BankLtd." Treasury notes should always be sentregistered post. Advertisements, together withremittance, should be sent to the ClassifiedAdvertisement Manager, Everyday Electronics,Room 2337, IPC Magazines Limited, King'sReach Tower, Stamford St., London, SE1 9LS.(Telephone 01-261 5918).

CONDITIONS OF ACCEPTANCE

OF CLASSIFIED ADVERTISEMENTS

1. Advertisements are accepted subjectto the conditions appearing on ourcurrent advertisement rate card and onthe express understanding that theAdvertiser warrants that the advertise-ment does not contravene any Act ofParliament nor is It an infringement ofthe British Cod* of AdvertisingPractice.

2. The publishers reserve the right torefuse or withdraw any advertisement.

3. Although every care is taken, thePublishers shall not be liable for clericalor printers' errors or their cons. -q

MiscellaneousARMATURES, Armatures B and D. Wolf.Bridges Makita etc. Exchange armaturesand fields for most power tools obsoletemodels covered. S.A.E. for quotation orring 061-799 0624. INTER -Q -CONTROL, 26Broadway, Worsley, Manchester.

EVERYDAY ELECTRONICS PCB'sIn top quality glass fibre tinned and 4rilled. Forfull list and current boards please send SAE alsoproduced from customers own masters pleasesend for quote.PROTO DESIGN. 4 Highcliffia Way, Wick -ford, Essex SSI I IlLA.

DISCOVER THE PLEASURE of ElectronicGames, including TV Football, Tennis,Squash, Practice; TV Tank Game; Battle-ships; Noughts & Crosses; Roulette. Cheapand easy to build (TV Football less than£10). Eight circuits, plans for only £1-85.Orders to: RIDLEY PHOTO/ELECTRONICS,Box 62, Uckfield, Sussex (reg. office, Wall -send House, Pevensey Bay, Sussex).

1119 RESISTORS 75pTV/ 5% c/FILM 2 2C1-2 2M fl (E12)

10 each of any valueSend stamped envelope for fres sample

COO CASSETTES 309 All Cassettes In Plastic Case1190 CASSETTES 450 with Indes and Screwed

Assembly.All Prices Include VAT. Add Postage 10p In LIQuantity Discounts SALOP ELECTRONICS,10 Unita 5% D WYLE COP,SO Unite 7% SHREWS111

100 Units 10% Tol.1.121111 URY.

METAL DETECTOR KIT type "MD l"(Home Office approved). Supersensitive.Operates with Transistor radio, only £3-75.VOX KIT "A03-VR" High performance.Relay output module £9.75. Other easy-buildkits available. 16p stamps for illu-strated catalogue. WELLTEX Co., 9 SirdtrStrand, GRAVESEND. KENT.

RECHARGEABLE BATTERIES'AA' pncall (HP7) LI 32; Sub C LI 64. C (H PI I,L2 43; '0' (14P2) L3.56; PP3 L4.98. Matching ch16.98 each except PP3 ch L582. Chargingholders for 2, 3. 4, 5 or 6 Nansens 50p. 'C' a 'D' sizeholders. 4 cells only 130o. Prices include VAT. Add 10%post package and insurance orders under L20. 5% overL20. SAE for full details plus 7Sp for 'Nickel CadmiumPower' booklet. Mail orders to SANDWELL PLANTLTD.. Dept. SE. 101 Monmouth Drive, SuttonColdReld, West Midlands. Tel 021 3349764. Callersto T.L.C., 32 C Street, Charing Cross,London W.C.2.

"250/12 Volt inverters now available"

LIST No. 23 NOW READY. Styli illustratedequivalents also cartridges, leads, etc. Freefor long SAE. FELSTEAD ELECTRONICS(EE1, Longley Lane, Gatley, Cheadle,Cheshire.

ENAMELLED COPPER WIREswg I lb 8 zo 4 oz 2 oz14-19 2.40 1.20 39 SO20-29 2.45 1.00 .32 5930-34 2.00 1.70 -39 -4435-40 2.85 1.90 104 75

Inclusive of p&p and VAT. SAE brings Catalogueof copper and resistance wires in all coverings.

THE SCIENTIFIC WIRE COMPANYPO Box 30, London E4 91IWReg. Office: 22 Coningsby Gardens

Amateur Clubs

THE BRITISH AMATEUR ELECTRONICS CLUBcan help you learn more about electronics Specialconcessions, practical help and new series for beginnersIn the B.A.E.C. Newsletter, sent to members quarterly.All four Newsletters for year from January 1st sent tonew members. Annual subscription: U.K. L3 50. Over-seas L4 50 surface or L5 50 airmail, payable in sterling.SAE for details to the Hon. Sec. J. G. MARGETTS,42 Old Vicarage, Green, Keirnshem, Bristol.

Receivers and ComponentsCOMPUTER MODEL KITS. Suitable begin-ners or as introduction to computer circuits.Transistor and IC types available. Pricesfrom £7-50. SAE details. TRANTER, TheOrchards, Buttgate, Grainthorpe, Lincoln-shire.

NO LICENCE EXAMS NEEDEDTo operate this miniature, solid-stateTransmitter -Receiver Kit. Only £9.75plus 25p P&P.'Brain-Freeze'em with a MINISTROBE Kit, pocket -sized 'lightningflashes', vari-speed, for discos andparties. A mere £4.10 plus 20p P&P.Experiment with a psychedelicDREAM LAB, or pick up faintspeech/sounds with the BIG EARsound -catcher, ready-made multi-function modules. £5.00 each plus20p P&P.LOTS MORE! Send 20p for lists.Prices include VAT. (Mail orderU.K. only).

BOFFIN PROJECTS4 Cl2NLIFFE ROAD, STONELEIGH

EWELL, SURREY. (E.E.)

DISCOVER ELECTRONICS. Build fortyeasy projects including: Metal Detector;Wireless Transmitter; Breathalyser; Radios;Stethoscope; Lie Detector; Touch time -switches; Burglar Alarms, et( . Circuits,plans all for £1.29 including FREE circuitboard. Mail only. RIDLEY PHOTO/ELEC-TRONICS, Box 62, 111 Rockspark Road,Uckfield, Sussex.

Electronic Timers UpMini Electronic Buzzers11/9/12 Volt DC 311pMini Buzzer 12V AC Sip800 Mini Speaker 4914Loud Sirens 6 Volt DCL1 31 ea. Buzzer Alarms11 Volt DC 1.5pKey Switch + Key L1-12Small Reed Switch 14pLarge Reed Switch 12pReed Magnets Op a 12pLarge ,, Circular lapReed Relay 3-12V DC lipOn Earphone £ Plug tipEnamelled Copper Wire32.34, 3d.Large Red/Clear LEDs fsp8C10718/8 12p ORP12 75p

Resistors 1W 5% 10Prices include V.A.

15 Watt Miniature 250VSoldering Irons L3 87Stabilised Power Supply8 Volt 120mA L.1 ISMains Motor 250 RPM250V AC 49p TrimphoneWarbler Unit UpCalculator Keyboard 59p240V Solenoids LI 30Pots 10K 1M Lin lipComponent Panel 111pCroc. Clips Red/Black Tp40 Assortment Pak 44p25 Asstd. Capacitors 5Op30 Untested 0,491 241p20 Untested AC128 30025 Untested IC's 39p30 Transistors 311p50 Asstd. Resistors 39p

ohms -10 Meg 20 ea.T. Add 18p Postage.

GRIMSBY ELECTRONICS$4 T ., CLEETHORPES. HUMBERSIDECallers to our Lambert Rd.. Grimsby Shop. 100s ofBargains -Components, Cases, Pots. Vero, Relays.etc. Open Tues., Wed., Fri., Sat. 19-5.3e p.m. ListNo.14 10p. ADVERTS from DEC. ion STILL VALID


71b ASSORTED COMPONENTS £295. SmallAudio Amplifiers. 3 transistors equivalent toAC128. 0072. with circuit. 3 for £1. 300small components, Transistors. Diodes fl .30.No Postage, list ISp refundable. Insuranceadd 15p. J.W.B. Radio, 2 BarnheldCrescent, Sale, Cheshire M33 1NL.

COMPONENTS FOR E.E. PROJECTS.Component lists with prices available for all E.E.projects from October 1977 onwards, includingTeach -In 78. Send S.A.E. stating project andmonth of publication (maximum 4 projects perS.A.E.). List sent by return together with ACEorder form/catalogue.ACE MAILTRONI X, Tootal Street, Wake-field, W. Yorks. WF I SJR.

EducationalHOLIDAY FOR BOYS, 14-11i rears. JULY/AUGUST 1978. Tuition and practical workin Engineering IKartingl, ElectronicsRadio Production and Tape Recording antiPhotography. Nine days in Norfolk. £34.Write for free brochure. INTER SCHOOL.CHRISTIAN FELLOWSHIP. 0 Ashcroft,Old Bolingbroke, Nr. Spilsbs. Lincs.

Service SheetsBELL'S TELEVISION SERVICE for servicesheets of Radio. TV etc. 75p plus SAE.Colour TV Service Manuals on request.SAE with enquiries to BTS, 190 King'sRoad. Harrogate, N. Yorkshire. Tel: 042355885.

SERVICE SHEETS for Radio, Television,Tape Recorders, Stereo, etc. With freefault-finding guide, from 50p and s.a.e.Catalogue 25p and s.a.e. Hamilton Radio.47 Bohemia Road, St. Leonards, Sussex.

PLEASE

MENTION

EVERYDAY

ELECTRONICS

WHEN

REPLYING

TO

ADVERTISEMENTS

DENCO(CLACTON)

LIMITEDDept. E.E.

351-13-9 OLD ROADCLACTON -ON -SEArSSEX C015 3RH

Our components arechosen by technicalauthors and con-structors throughoutthe world for theirperformance and re-liability, every coilbeing inspected twiceplus a final test and

near spot-on alignment.General Catalogue showing fullprodoct range 36p. Overseas Cus-tomers 70p, Air -Mail Post Paid.

U.K. & OVERSEAS MANU-FACTURERS/STOCKISTS

ENQUIRIES WELCOME

Australian Readers Please Note-Our Complete Range of Coils areavailable from Watkin Wynne Pty.Ltd., 32, Falcon Street, CROWSNEST, 2065, AUSTRALIA. P.O.Box 392.

TUACTRANSISTOR UNIVERSAL AMPLIFICATION CO LTDPHONE 01 672 3137 672 9080MANUFACTURERS OF OUALITV AMPLIFICATION AND LIGHTINGCONTROL SYSTEMS

NEW FROM TUAC

ULTRA QUALITY HIGH POWERNew D.C. Coupled Design

AMPLIFIERSFeaturingElectronicElectronic Short Open and Thermal Overload Protection.Brief apse.Input Sensitivity 0.775 v. R.M.S. (0.0.8.) at 25K Ohms.Frequency Response 20 Hz - 20KHz.Hum and Noise -100 dB Relative lull output.T.H.D. at full power 0 1%.T.D. 500 300W Into 2 Ohms.

220W Into 4 Ohms.Size 7" 9" x If" 140W Into 8 Ohms.. L45 SOPower supply P.S. 300 .. [28 SST.D. 150150W into 4 Ohms5" r 2" 100W into 8 Ohms L26 25Power supply P.S. ISO .. VG 2ST.D. 15060 Version SOW into 8 Ohms .. LIT 755" 5" 2" 40W Into 15 OhmsPower supplies P.S. 80 .. L15 25Note-P.S. 300 will drive 2 T.D. ISO amplifiers.All output ratings are R.M.S. continuous sine wave output.

TO ORDER BY POSTMake chaques/P.O.s payable to TUAC LTD., (EVA) or quote Access/Barclay Card No.(We accept holders phone orders 01472 9080).Post to-TUAC LTD.. (EEGS). 119 CHARLMONT ROAD. LONDON SW.17 9AB.Send stamp for our free 28 page catalogue of LIGHTING 6 AMPLIFIER MODULES, etc.

E.E. PROJECTSCHASER LIGHT DISPLAY. Feb78. L19 56 inc. p c.b. Case (3 47.A.C. plETOR CON . Feb,78. C4 25 inc. case.AUDIOTEST. March 78. L19 91 lesscase. Front Panel 66p.CATCH A LIGHT. March 78. E4 32.Case CI 32. Switch cases 55p each.C R SUBSTITUTION BOX L6 20.Case CO 97 11W Raisistors .

WEIRD SOUND EFFECTS GEN-E RATOR. March 78. L3 63 inc. cam.E LECTRONIC TOUCH SWITCHJan 78. L I 44.AUTOMATIC PHASE BOX. Dec.77 L9 83 inc. p.c.b. and case.CAR SYSTEM ALARM. Feb. 71.13 68 inc. case.AUDIO VISUAL METRONOME.lar. L3 59...c case

POCKET TIMER April. 78. (4 09inc. cmTRANSISTOR . Oct. 77.(6 40, use extra C2 98.PHOTOFLASH SLAVE. Dec.E3 68 inc. case. Less lead.VHF RADIO. Nov. CIO 20 inc. case.TREASURE LOCATOR. Oct.L7 98 Case (2 49.SHORT WAVE RECEIVER. Aug.C9 39. Case CI 55.DICE. March. (4 24 inc. case.SOIL MOISTURE. lune. L2 95 inc.case and probe.PHONE DOORBELL REPEATER.July. £4 70 Inc case.RAPID DIODE CHICK. Jan. i2 12inc. case.PUZZTONE UNIT. July. LS 75vc use.ADD ON CAPACITANCE UNIT.Sept. £4 SO inc. case.CONSTRUCTIONAL ARTICLES290 each

1978 COMPONENTS CATALOGUE MAGENTA Magenta gives you a w,de range or the things you need -components -tools -hardware -and lots more. First-class delivery. NO minimum order. Inclusiveprices. All products stock lines. Illustrated catalogue with data. Send 2 x 9pstamps.This Catalogue is MUST for go Ls. Write Today I

AMPLIFIER MODULE -STEREOI I + 12W. 8 ohms. Tone Vol. controlsplus Fascia 9V D.C. L4 90.SIGNAL INJECTOR AF RE probeand lead. L4 98.MULTIMETER. TYPE 1.1.000 o.p.v.with Probes. 2. 3j l LS 95.MULTIMETER. TYPE Z. 20,000o.p.v. with case and probes 5' 74'

It LIO 95.ANTEX XIS SOLDERING IRON25W. Ideal for electronics L3 613SOLDERING IRON STAND.ANTEX ST3 LI 55.DESOLDER BRAID. 62pHEAT SINK TWEEZERS 123p.DRILL. 12 VOLT. 10.000 ...p.n.Hand or stand use CIO 05.DRILL STAND. Adjustable height.LS SI.TRANSFORMERfor 11V drill (15 37.B UZZER. 6V. 74p.INTERCOM. 2 station desk model,Cable and battery L5 9S.HEADPHONES. STEREO. 8 ohm.13.15 KHz. Padded L3 85

HEADPHONES. MONO. 2Kohms. Sensitive. a 50.PHONE PICK-UP COIL. 3 Smrnplug. 65P.EYEGLASS. Jewellers magnification

3 93o.TRIPLE MAGNIFIER. Each lens

5 magnification. CI IS.DENTISTS MIRROR. Adjustable

i 70.SCREWDRIVER SET. 6 miniatureieweliers type, in case. L2 40.SPEAKERS. Miniature (I ohm S9p.64 ohm 13Sp. 80 ohm LI 15.EARPIECES. C 139o. magneticISpF.M. INDOOR AERIAL 49p.S -DEC t2 20.T -DEC C3 98.U -DEC L7 58.TELESCOPIC AERIAL. 6 section.70cm. 9Sp.

MAGENTA ELECTRONICS LTD., EES, 61 Newton Leys Burton -on -Trent, itaft, DEIS 00W. 0283-65435.

TEACH -IN '78 COMPLETE KIT £13.95


SUSI-Nitathe quickest fitting \CLIP ONcapacitive discharge.,#----electronic ignitionin KIT FORM ....IntroductorySPECIAL OFFER£2 OFF Smoother running // Instant all-weather starting Continual peak performance Longer coil/battery/plug life Improved acceleration /top speeds Optimum fuel consumptionSparkrte X4 is performance, high quality capacitive discharge, electronicignition system in kit form. Tried, tested, proven, reliable and complete. It can toassembled in two or three hours end fitted in 1/3 mina.Because of the superb design of the Sparkrite circuit It completely eliminatesproblems of the contact breaker. There is no misfire due to contact breakerbounce which is eliminated electronically bye pulse suppression circuit whichprevents the unit firing if the points bounce open at high R.P.M. Contact breakerburn is eliminated by reducing the current to about 1/50th of the norm. It willperform equally well with new, old, or even badly pitted points end is notdependent upon the dwell time of the contact breakers for recharging the systemSparkrite incorporates a short circuit protected inverter which eliminates theproblems of SCR lock on end, therefore, eliminates the possibility of blowing thetransistors or the SCR. (Most capacitive discharge ignitions are not completelyfoolproof in this respect). The circuit incorporates a voltage regulated output forgreatly improved cold starting. The circuit includes built in static timing light,systems function light, and security changeover switch. All kits fit vehicles withcoil 'distributor ignition up to El cylinders.

THE KIT COMPRISES EVERYTHING NEEDEDDie pressed epoxy coated case. Ready drilled, aluminium extruded base and hestsink, coil mounting clips, and accessories. Top quality 5 year guaranteedtransformer and components, cables, connectors, P.C.B., nuts, bolts and silicongrease. Full instructions to assemble kit neg. or pos. earth and fully illustratedinstallation instructions.

NOTE - Vehicles with current impulse tachometers (Smiths code on dial RV1Iwill require a tachometer pulse slave unit. Price E3.35 int . VAT. post & packing.32 Beth Street Walsall WS1 3DE

ITADS PULSE SLAVE UNIT D.35

Electronics Design Associates, Dept. EE682 Bath Street. Walsall, WS1 3DE. Phone: 109221 614791

Name

Address

Phone your order with Access or Barclaycard

IK VAT. ad PP. QUANTITY REO

X4 ET 11441 tt1.16

ACCESS/BARCLAYCARD No.

I enclose cheque POs for

£Cheque No

Send SAE It brochure onA required

THIS is the Catalogue you Ireto solve your

componentbuying

problems!

The finest componentscatalogue yet published.

Over 200 A -4 -size pages. About 5,000 items clearly

listed and indexed. Nearly 2,000 illustrations. Bargain List sent free. At £140, incl. p. & p., the

catalogue Is a bargain.

Send the coupon below now.NOME RADIO (Components) LTD ept. EE., 234-240 London Road.

Mitcham, Surrey CR4 MID

Q . P/ease write your Name end Address in block capitals

' 44 INAMEh

104.'ADDRESS

yott I

I HOME240C1* a L34

2

RADIO (Components)London Road, Mitcham

LTDSorrier

Dept. EEC114 30.10

'Resin NoLondon 9129 4:

Becomea radioamateur.Learn how to become a radio -amateur in contact with the wholeworld. We give saled preparationfor the G.P.O. I icence.

Brochure, without obligation to:

BRITISH NATIONAL RADIO& ELECTRONICS SCHOOL,

P.0 Box 156, Jersey, Channel Islands.

WAA

EE

NAME

ADDRESS( Bi ock cane foielem).

Published approximately the third Friday of each month by IPC Maga:toes Ltd.. Pleetway Room, Parr ngdon Bt., London EC4 4AL. Printed In England by IndexPrinters Ltd., Dunstable, Beds. Bole Agentsfor Australia and New Zealand-Gordon and Gotch (A/81a) Ltd. South Africa-Central News Agency Ltd. Everyday Electronic* is sold subject to the following conditions namely that it shall not, without thewritten 00120111t of the Publishers Ant given, be lent. resold, hired out or otherwise disposed of by way of Trade at more then the ,.commendedgalling prior shown on cover, excluding Eire where the sellingprim is subject to V.A.T.. and that It Alail not be lent, resold, or hired out or otherwise disposed of In s mutilated condition or In any unauthOrissd cover by way of Trade, or sexed to or as part of anypublication or advertising, literary or pictorial matter whatsoever.

Marshci's ti9er'a pear'clealCall in and see us 9-5.30 Mon -Fri 9-5.00 SatExpress Mail Order TeL orders on credit cards £10 min.Trade and export enquiries welcome

A. Marshall (London) Ltd, Dept EE London : 40-42 Cricklewood Broadway, NW2 3ET Tel 01-452 0161/2 Telex: 21492 & 325 EdgwareRd, W2 Tel 01-723 4242 Glasgow: 85 West Regent St, G2 2QD Tel: 041-332 4133 Bristol: 1 Straits Parade, Fishponds Rd, BS16 2LXTel: 0272 654201 PLEASE NOTE ALL OUR PRICES NOW INCLUDE VAT

TRANSISTORS2146962146972N6982146992147062N706A2N7082147182N718A214720A2147222147272149142149162149172N918214929214929,42149302N930A214171121418892N189021418932N2102214219221421932N2193A2N21942N2194A2N2195

39 2N2195A31 2N221749 214221858 2142218430 214221930 2N2219A30 2N222030 214222154 2N222I A85 2N222245 21422224SO 214236938 2N2369A33 2N264638 214264745 2N290337 2N290437 2N2904 A37 2N290595 2142905.430 2N290630 2N2906A30 2N290730 2142907450 214292358 2N292450 2N292552 214292642 214305345 214305440 2143055

2143390 50 21..,- 182143391 40 215 18

5555 2143392 17 2144 6540 2N3391A IS 2154

35 2143393 17 2144' - 7238 2143394 17 264, 6031 2143395 19 2144 2239 2143396 19 2144.. 1739 214339% 19 21.14 ' 2225 2143438 85 2N, ' 1925 2143440 75 2144'.. 2025 2N3441 92 2N4'... 3525 2143442 45 2144 .1 6527 2143638 17 2144'. 2727 21436384 17 2780 2143702 14 2144' 1955 2143703 14 2144 .. 1960 2143704 14 2144 . 1931 2143705 14 2144 '. 1931 2143706 14 21442.. 3831 2143707 14 2144,.. 2231 2143708 12 2144. 2225 2143709 12 2144. 2225 2143771 16 2144. . 2225 2143772 20 2144 . 2025 214377.3 15 2154 .. 6517 2143819 36 2144' 6517 2143820 39 2144' 7019 2143821 96 2144,.. 8317 2143900 28 21445. 5425 2143901 30 2144.-. 6072 2143903 20 2144'. 7575 2143904 II 21.44.. 15

LINEAR CIRCUITSCA3"18CA40184CA3020CA3020ACA3028ACA302813CA3030CA1030A,CA3038CA30313ACA3045CA3346CA3048CA3052CA3080C A 30804CA3086CA308813CA3089BCA30900CA3130CA3140LM301LM307NLM308NLM309KCLM317KLM318NLM32015LM320112LM320115LM320124LM320P5LM320P12LM320P15LM320P24LM3231(LM339NLM34015LM340115LM340124LM341P5LM341P12LM341P15LM341P24LM348NLM358NLM360NLM370NLM371 HLM350KLM373NLM374NLM377N

7510205090255020901055774573851050879040060430509595354516151515151515IS956088888880808080956000303545353680

LM378NLM379SLM380N8LM380N14LM381 ANLM381 NLM382NLM384Nt M386NLM387NI.M388NLM389NLM702CLM703LM7098LM70914LM710LM71014LM711CNLM723CLM723C14LM726LM741CLM741C8LM741C14LM747CNLM7488LM74814LM1303NLM1304NLM1305N

M1307NLM1310NLM1351N

M1458NLM1496NLM1808NLM1812NLM1820NLM1828NLM1830NLM1841NLM1845NLM1848NLM1850NLM1889NLM3301N

M3302NLM3401 NLM3900N

M3905NM3909N

LM3911NL M7805K

_8.478120 75LM324 75

40 LM7815K 7525 LM7824K 7596 LM78L060208 3070 LM7811269 3032 LM78LI5C55 3088 MM5314 6010 MM5316 6000 NE555 3300 NE556 8581 NE55AN 1 9870 NE560 d 5050 NE561 d SO49 NE562 4 5067 NE565 1 3964 NE566 1 7572 NE567 1 9075 NE57IN d 9545 SAS60 2 7080 SAS70 2 7070 SAJIIO 2 1030 5041P 1 3530 5042P 1 3599 SN7600I NI 30SO SN 76003N 2 3690 SN76013N1 SO15 SN76023N1 SO52 51576033142 3552 TAA263 1 3522 TAA300 3 7010 TAA320A30 1 IS45 T A A350A97 30010 TAA521 1 1020 TAA522 21016 TAA550 0 4890 744560 2 1090 TAA570 2 2090 T AA370A50 6 4598 TA A630 2 4090 TA A960 3 9090 TAA970 4 2060 144611E12 SO55 TAA621 2 5055 TA A661A68 1 6515 TAA661B1 4578 TAA700 4 SO10 TAA930A1 4575 TAA930B1 45

UAA.170UA A1130TLOECCPTLOtICP11.662CPTLOE1CNILOIACNLF35514LF35651

0080243435486070354560706080

00102020

TA13'..01134120TB/ -.'00TBA 7200T/341'0TBA''00TBAY21)TBA 7200TBA7'.0re.41-,007134'40184-+_400TBA` 50TBA7.100TBA16000

TEIA!,70TEI4E7013TBA,7600TBA720A0

2 06TBA;50 2 36TBA7F,00 2 45TBALOI) 1 30TBAE.05 1 30784.120 0 80184920 2 99TCA.60C 2 36TCA 60132 iiTCA270 2 99TCA.730 4 50TC4.740 4 50TCA750 3 00TCA760 2 00TCA105 1 49TCA440 1 651041022 7 50TDA1024 1 24IDA.034 4 75TDA2020AD

501515250

91040458080

LF35714 0 80LF1'..201N 3 00LF13...3IN 3 00LF12741H 0 80LF1,741N 0 SS

LEDS + OPTO

Displays 7 seqcorn anode oroath Red8mrn HT LI SO10nInt HT El SS14mni HT El 57Ifirnm HT CI 85

LEDS Red Gr YellSmall 3men 18 19 19Large 5mrm 20 20 26xtra bright 40 40 40

I red LD271 £0 SSIR receiver E1 45Opto coupler E1 SO

Full range + data in out 1978 catalogue

2145086

148230 214510: 45 AD161 00 BC168B 13 BC184LC 5

2145087 30 2146108 55 00 801680 13 BC212 .521450882145089

3030

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5549

A1106 6052

BCI698BC169C

1313

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.515

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6575

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41

449C107BC107A 6186 BBCCII7777A

2222 12tBBCC2212 A 9',8

2145192 80 2145123 48 BC107B 16 BC17713 25 BC212LB '82N5193 75 2145124 45 BC108 16 BC178 22

BB22211A.5

2N5194 80 2N5125 47 8C1084 16 BC1789 25 .52145195 97 40361 55 BC108B 16 BC17813 35 BC213B :521452452145246

3738

4036240363

45 55 080C130109

1716

BC179BCI79A

2525 BBC2C2133LC .75

2145247 44 40408 82 8C109B 17 BC1798 25 EIC213LA 7214524821452942145295

444444

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82

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32

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261212

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7

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72145296 44 40594 913 BC1828 13 BC2148 '72145298 44 40595 987 BB211,17713 13 BC182L 15 BC214C 172145447 16 40673 8013 BCI82LA 15 BC2I4L T82145448 16 40669 30 BaCCIXL3 13 BC182LB 15 f3C214LB 182145449 20 AC126 48 BCI48C 13 BC183 12 8C2141C2145457 38 AC127 48 BC149 15 BC1O3A 12 BC2378 '52145458 35 AC128 48 8C149C 15 BC18313 13 BC238A .32145459 32 AC151 43 BC157A 15 BC193C 13 BC238B 32145460 65 AC152 54 BC158A 15 8C1133L 15 BC238C 32145484 37 AC153 59 BC158B 15 BC183LA 15 BC2398 162145485 40 4C1531( 59 BC159A 17 BC183LB 15 BC239C 172145486 40 AC176K 70 BC159B 17 BC183LC 15 BC?57A II2145490 64 AC176 54 BC160 38 BC184 12 8C2588 T92145492 64 AC187 59 8C161 38 0C18413 13 BC2598 192145494 65 AC187K 65

C13 3C184C 13 BC300 43

2145496 67 AC188 54 BBCI16677B 13 9C1841 15 BC401 CI2146027 64 AC1886 65 BC168A 13 .3C18416 15 BC302 37

BC303 54 BDI39 0 43 BU530 55BC307 19 BD140 0 43 805J5 70BC307A 16 BD181 1 90 BD536 70BC307B 16 801132 20 BD537 74BC308 16 BD183 35 BD538 77BC3013B 16 BD187 95 80539 60BC3094 16 BD235 46 8D540 60BC309B 16 80236 44 80014 32BC309C 16 80237 44 BOX18 90BC327 22 1313238 44 BDY20 10BC328 20 802394 44 BDY55 90BC337' 20 B0239C 59 1313056 10BC338 23 BD240A 49 13E115 39BC547 13 BD240C 59 81160 33BC547A 13 BD241A 49 BF161 65BC54713 13 BD24IC 65 131167 378C548 13 B0242A 55 81173 37BC549 14 BD242C 62 81177 27BC549B 14 BD243A 65 BEI 78 27BC549C IS BD243C 87 8E179 33BC557 14 BD244A 70 81180 3713C558 13 80244C 87 131181 37BC559 IS BD245A 69 81182 37BCY70 21 80245C 85 8E183 44BCY7I 26 BD246A 72 131184 41scx-. 18 B0246C 93 6E185 37BDil5 88 130433 44 8E194 16013131 55 80434 46 81195 1690132 75 130435 46 81196 16BDI35 40 80436 46 8E197 18BD136 40 80437 55 8E198 198013. 41 BE3438 55 81199 19813138 41 130529 49 BF224J 22

TTL & CMOS 7485N7486N

3636

'4LSI51N SI1 .4C 17314 90 7489N 45AL 5154N 45 /4C174N 90 7490AN 45:41.5155N 20 74C175N 90 7491414 85/4L5156N 20 74C192N 11 7492N 4574LS157N 60 74C193N 11 45'4LS158N 65 74C195N 90:4 LSI6ON 43 7400N 76'4LS16IN 85 740114 749615749414 70'41_5162N 43 7402N 17 7497N 95741.5163N IS 7403N 17 74100N 1 40'4L5164N 43 7404N 17 74107N 35'4LS168N 43 7405N 22 74118N 95.4L5169N 43 740614 56 74119N 40%4LS174N 33 7407N 55 74121N 2814L5175N 26 7408N 22 74122N 5574LS181N 95 7409N 22 74123N 5574LS189N 74 7410N 20 74125N 4574LS190N 00 7411N 26 74141N 8674LSI9IN 00 7412N 20 74148N 35'4LS192N 98 7413N 36 74145N 8674LS193N 98 7414N 80 74150N 20'4L5196N 28 7416N 36 74151N 76'4COON 24 7417N 36 74153N 76'4CO2N 24 742014 22 7415414 20'4C04N 24 7423N 32 74155N 70'4C08N 24 7425N 32 74157N 78.4CION 24 7427N 32 74160AN 10.4CI4N 41 7430N 22 74161AN 1074C20N 24 7032N 30 74162AN 1074C30N 24 7437N 35 74163AN 1074C32N74C42N

24 7438N92 744014

23 02 6427441165NN 3366

74C48N 38 7441 AN 84 74167N SO74C73N74C7415

54 7442N56 744514

4706 2744117245NN 6000

74C76N 54 7446AN 90 74176N 9074C83N 30 7447AN 80 74177N 9074C85N 30 7448N

929274C86N 64 7450N 77:11899INN 0909

74C89N 39 7451N 22 7418214 8074C90N7409314

85 7453N85 745414

2222

74195N741854N

5050

74C95N 04 746014 22 74788414 2574C107N74015014

22 7470N14 747214

430 67418915 60

74C151N 47 7473N 41 74190N 40

7744211551NN 6$ 7474N21 747514

3280

74191N74192N

2020

74C160N 11 7476N 45 74193N 2077442116621NN 11 748014

11 74811460 7419614 20

74C163N 11 748215 74197N 00

74C164N 04 7483N as 74198N 0074C165N 04 7484N 20 74199N 00

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OIL SKTSLow profile IC skis8 pin 15p 22 pin 301,

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CONVERT TV SET TO TELETYPEThe new CRT control chip from Thomson CSFSFF96364. Convert your TV set into an electronicteletype -16 lines 64 characters, requires RAM,character generator 6 little else for a basic teletypeAvailable as chip or full display card. Full curs.,control, 5 volts TTL compatible. hoe erase. full cardincludes DART, Modern, char, gen etc, con,video out front encoded keybd in.

NEW chip £1720Full card E151 00

*MAIL ORDER*Express service on allorders, please add 40pfor p&p to all orders.Tel orders on creditcards £10 rurnrnrurnr 31 DIGIT PANEL METER KIT

INTERSILLCD DisplayEatt operated NEW !Contains allcomponentsrequired for constructionrids PCB. Auto vero extremelyversatile and accurate -easyassembly kit.f2699

CLOCK MODULES DIGITALEuill aedswitches and transformer to complete12 or 24hr alarm modulesPIIA1002F 12hr Sin display 10 45MA1002H 24hr Sin display II 45MA1010E 12hr 84in display 13 TS141A1010G 24hr 84in display 13 75

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AUDIO MIXERA superb stereo audio mixer. It can be equippedwith up to 16 input modules of your choice andits performance matches that of the very besttape -recorders and hi -fl equipment. It meets therequirements of professional recording studios.FM radio stations, concert halls and theatres.Full construction details in our catalogue. Acomponent schedule Is available on request.

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REVERBERATION SYSTEMSHigh quality spring line driver module uses 4 integrated circuits and two transistors. Built and testedcircuit board with wiring instructions for spring lineXI385G, price 1.11 H. Power supply to suit drive.module costs around E2.58 and construction details

are in catalogue, or ask for leafletMES24. Mechanical spring lines'Short line (XLO8J) L4.411; Long line(X1584F) £10 30. (All prices IncludeV.A.T. and p p).

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t14811 · IC radio chip £1.05. Extra parts and peb for radio £3.85. Case LI. Send s.a.e. for free...

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Transcript of t14811 · IC radio chip £1.05. Extra parts and peb for radio £3.85. Case LI. Send s.a.e. for free...