Every oz1 Thursdalik) - World Radio History

AMATEUR WIRELESS, MAY 18, 1921

YOU OUGHT TO BUILD OUR NEW PORTABLE!

Every oz1Thursdalik)

Vol. XIV. No. 362 Saturday, May 18, 19

PE 1-44111 TEST ErefirRegistered at the .P.O. as a Natesaaaar

anal. wtrehn 11MAY IS 1929

Of course Mullard P.M. valves make anyset, but just now we are particularly re-ferring to the amazing performance of thenew Mullard Screened Grid and Pentonevalves in the Mullard S.G.P. Master Threereceiver

To cut a long story short, we knew thaton paper the circuit was a winner. Wefound on test that the Mullard ScreenedGrid and " Pentone " valves turned it intoa world-beater.

MullardTHE MASTER. VALVE

Advert: The Mullard Wireless Service Co., Ltd., Mullard House, Charing Cross Road, 'London, W.0 2.

To Ensure Speedy Delivery, Mention "A.W." o Advertise.7s

MAY 18 1929701 nulteurFWD

Greater selectivity andproved tone is the responseof your receiver when you doit justice by fitting LEWCOSCENTRE TAPPED COILS.The high standard of qualityand skilled workmanshipwhich are characteristics ofall LEWCOS PRODUCTS isyour guarantee of perfectservice.Leaflets, diagrams and fullparticulars will be sent freeon request.

... 1 t9

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Lewcos Radio ProductsFor Better Reception :

I ORIABLE 1. 63 ,voltsPORTABLE 2. 99 ,,PORTABLE 3. 108

Obtainable very**, eThere's a suitable _EVER IttADY replacementbattery for every Portaple.

4 dvert. of The Ever Read. Co.:(433.) Ltd., II ercql," Place, Lyndon, I V ,7

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Patent 271384

The LONDON ELECTRIC WIRECOIVPANY &SMITHS LIMITEDCHURCH ROAD, LEYTON, E.10

'Phone : Walthamstow 2531.'Grams : " LEWCOS, PHONE, LONDON,"

Trade Counter and Cable Sales :7 Playhouse Yard, Golden Lane, London; E.C.1

1 Maximum Inductance is ensured by closemagnetic interlinkage between turns.

2 Minimum Self -capacity is ensured by scien-tifically spaced sectional windings.

3 Citcuit Adaptability. Coils are interchangeableand you have an option of centre tapping.

4 Constant Magnetic Centre. All coils have thesame external dimensions.

IAWAIWCOSRegd

CENTRE TAPPEDCOILS

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mateurWirtle.5 702 MAY 18, 192g,

SAFE!.

The double lengthCossor filament famed forits colossal emission. Notethe seonite bridge holdingit rigidly in position.

W.1111,

3. Note the enormousstrength and rigidity ofthe screen. Built on fourstout supports, capper( bya metal bridge -piece an-chored to seonite insulator

2. Around the twostout grid supports iswound the first grid,electrically welded' attwenty-five points.

4. Finally, observe theconstruction of the anode.Actually two rectangularnickel plates are usedand for greater rigidityeach is diagonally ribbed.

INTERLOCKED!

Made in 3 types for use withZ, 4 and 6 -volt Accumulator

Max Anode Volta ISO, Impedance200,000, AmplificationFactor 200,Grid l..voltsvolts at max. anode Volts. 22/6

Price k either type)

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Cossor makes greatestadvance in valve designsince the introductionof the Dull EmitterThe wonderful new Inter -locked Construction em-ployed in the Cossor Screened Grid Valve eliminatesall the inherent weaknesses in valve design. Underthis system (illustrated here) each element isfirmly braced top and bottom. Every joint isscientifically welded. This girder -like constructionensures absolute rigidity. It positively preventsthe slightest individual movement of the elements.Even the hardest blow cannot disturb their perfectalignment.

As a result the Cossor Screened Grid Valveretains life-long uniformity of its characteristics.Its Inter -locked Construction (exclusive to Cossor)makes it the strongest and most robust ScreenedGrid Valve ever produced. Use Cossor in your

Screened Grid Receiver -there is no substitute for theCossor patented system ofInter -locked Construction.

Only Cossor ScreenedGrid Valves have inter-locked Electrodes

CossorScreened GridBRITAIN'S STRONGEST AND MOSTDEPENDABLE SCREENED GRID VALVE

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Mention of `itimateur Wireless" to Advertisers will Ensure Prompt Attention

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l'.. MAY 18, 1929 No. 362. Vol. XIV '

N 'SS S

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5 5

and Racliovisions s§5

5 The Leading Radio Weekly for the Constructor, Listener and Experimenter5§ = Editor : BERNARD E. JONES =----

§ Technical Editor : J. H. REYNER, B.Sc.. A.M.I.E.E. :: Research Consultant:. W. JAMES :: Assistant Editor : H. CORBISHLEY §

A Surfeit of Politics-Those Morning Talks-How It Is Done-Talkers and Big Figures - Exit Rex-Popular Concerts

A Surfeit of Politics-A dailypaper ran a competition in connec-tion with readers' comments onbroadcast political speeches. Oneof the received comments was verysuccinct. " I must congratulate-on his clear level voice, which gaveme the opportunity to make a fewvery gratifying adjustments to theloud -speaker." The B.B.C. hascertainly "done us proud " thisyear so far as politics are con-cerned, and by the time the GeneralElection is over, those who are un-patriotic enough not to care whichparty gets into power will be thank-ful -that "Mike" has overcome hiswave of controversial talk. Inci-dentally, the Secretariat of the CommunistParty has sent a letter of protest to the'B.B.C., demanding the same broadcastfacilities as the other parties.

Those Morning Talks-It is welcome'news that the morning talks are now broad -!cast from 2LO, as well as from 5XX. Theinnovation of morning talks from 5XXonly was introduced in January last, and aB.B.C. official told an AM'ATEUR WIRELESS!representative that this would be simply anexperimental service for four months. At,the start listeners were invited to expressopinions on the talks. It has been found;that these practical talks at 10.45 a.m. have

Modern Jack's Beanstalks-the beginnings of the masts at theLondon Regional Station at Brookmans Park

real ' low-down number.' " Incidentallythis " low-down number " was S.B. throughtwenty-one stations of the N.B.C. group.

Talkers and Big Figures-Talkerfilms are now " going big," to use anotherAmericanism, and it is rumoured that JohnMcCormack, the famous tenor, is to receive

ioo,000 for taking part in a "one -feature"picture. Incidentally film fans will beinterested to know that after seventeenyears' screen silence a Mary Pickford talkerhas just been released. A short time agothere was a miniature "scare" when anumber of B.B.C. folk went over to thegramophone and talker spheres. It is to be

hoped that all the talent will not berobbed from broadcasting, and thatfigures like the ioo,000 offered toMcCormack will not put the B.B.C.coffers to shame.

QSL Cards -Here's an itemfor DX fans and amateur trans-mitters. We apparently fell intoerror in stating that the R.S.G.B.will not handle QSL cards to orfrom non-members. It should beparticularly noted that the R.S.G.B.will accept and deliver all QSLcards to persons sending stampedself-addressed' envelopes to theheadquarters of the society at 53,Victcria Street, S.W.i.

Exit Rex-So Rex Palmer has gone theway of so many B.B.C. notabilities recently,and has left radio for the gramophoneworld. "Uncle Rex," who was Directorof the London Station for the first threeyears of its existence, is kindly rememberedby thousands and thousands. of listeners.Is the B.B.C. experiencing an influx of newtalent, or must we admit that the gramo-phone and talker -film people are gainingwhat ,will be a big loss to British broad-casting? So many seem to have left theB.B.C. recently for one or other of thesespheres.

Popular Concerts-Londoners whonow justified a permanent alloca- have not yet attended the popu-,tion in the programme. The post § , PRINCIPAL CONTENTS PAGE

',,.

703applications for recipes and menus Current Topics ..The B.B.C. Changes Its "Mike" 704 §referred to in the Tuesday morning 705 §§ Making an All -electric Gramophone ..broadcasts now number I4,000 !

C Are There Two Heaviside Layers? . 707§How It Is Done-The B.B.C. For the Newcomer .. 708 c

Press Notices are gravity itself, as s Jottings 708 .'§

From My Log ..befits a Government Department,On Your Wavelength ..

Secrets of the Test RoomRadio Beograd .. ..Without Fear or Favour.The Talisman Portable

r '. A .W ." Tests of Apparatuspep is only equalled - with her 722My Wireless Den .. ..

724 §avoirdupois, will share the honors Building Your Own Fultographwith Pil Spitalny . . ." "Also Miss .cc Broadcast Telephony .. 726 §Smith will croon 'Mean to Me' and § Our Information Bureau .. .. .. 729'Walking With My Sweetness,' a citev&,,te7),,t.e,&,,,,,,,..,t1teit,,,,_.),.i:Yi

bag in consequence is very big, and clar concerts relayed from thePeople's Palace, Mile End Road,London, E., should book the date atonce, for the last concert of thisseries is on Thursday next, May 23.There will be some good soloists andaltogether this is a B.B.C. outsideevent which should not be missed by

713711 the muscially-minded.but things are done just a little 5'differently in the States. For exam- § 714 § Listen for the Election-Nextple, we have at hand a programme 715 c week there is to be a 1929 edition ofsheet from WJZ which says : " Kate K.N 716 .v that very popular receiver "Britain'sSmith, that ' hot number,' whose S 720 S Favourite Two." Simplicity is the

great feature of this " two " and,together with the new version, willbe given hints on hooking up thecomponents so that they can be usedto get the election results.

emidair WireitT 704 MAY 18, 1929

THE B.B.C.CHANGES

ITS " MIKE "NLESS the London station trans-mission of the B.B.0 has a large

number of breakdowns ere these lines getinto print, a devastating change of micro-phone policy will have taken a firm hold ofSavoy Hill. The high -quality carbon micro-phone has had a long "run" at B.B.C.

RI

48.

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NEXTRPL/F/697;v.

STAGE

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Fig. 1. Method of coupling CondenserMicrophone

stations, and it is about to lose its job. Thecondenser microphone has at last passedits trials I

Hiss!For some considerable time the B.B.C.

has been dissatisfied with the performanceof the studio and "0.13." microphones.These microphones, mostly of the Reisztype, have given high quality but have beensubject to "blasting" on loud passages ofmusic and a large amount of backgroundhiss. From the maintenance point of view,however, they have given splendid service;in fact, I do not think there has been asingle record of a breakdown being causedby a Reisz microphone suddenly going" dud." But that hiss . . . It had to begot rid of, somehow.

The Condenser MicrophoneFrom time to time, the research and

development departments have broughtout new types of microphones, types whichhave varied from modified magnetophonesusing peculiar coils or iron filings to allkinds of electrostatic pick-ups. The electro-static pick-up is another name for thecondenser microphone, and in this type thesound waves impinge upon a tightly stretch-ed disc, varying the capacity of a condenserformed by that disc and a solid piece ofmetal behind. This was the type of micro-phone in which the B.B.C. placed its hopefor the future. Many times condensermicrophones were "tried out" on trans-mission after passing laboratory tests, but

By BAYNHAM HONRIthe percentage of breakdowns and" crackle " they introduced was too high tomake them of practical use.

DisadvantagesThe condenser microphone must neces

sarily be close to the first stage of amplifica-tion; otherwise capacity effects in themicrophone leads and other factors willdecrease the sensitivity and stability of themicrophone circuit. The circuit Fig. z

shows clearly why this is so, The condenserm is really a microphone, and two or threehundred volts of H.T. arc applied to one ofthe plates via a r5-megohm resistance.According to the variation in the capacityof mr, so will there be a varying drop in thevoltage across the large resistance RI. Thisvariation in voltage, which is very small,is passed on to the grid of a valve, througha small coupling condenser. The value ofthe grid leak, R2, is the same as that of themicrophone resistance.

Affected by DampnessUntil quite recently, dampness in the

atmosphere has affected the functioning ofcondenser microphones in various ways,causing "frying" noises and other inter-ference. The insulation between the platesof the condenser microphones must neces-sarily be high, or crackling noises will becaused by any leakage of current. Similarly,the insulation of the r5-megohm resistancerods and coupling condenser must be of ahigh order. I say "until quite recently"because the B.B.C. appears to have got overthis trouble and condenser microphoneshave been used on most musical trans-missions from 2L0 during the past twomonths.

Gramophone RecordingThe condenser microphone is not a new

invention. It has been used for some timeby the gramophone companies with greatsuccess, and more recently it has found itsway into the talking -film studio. In gramo-phone recording, the slightly "metallic"brilliance of a highly -sensitive condensermicrophone has been found to give more" clear cut" reproduction, particularly whenthe records were reproduced on ordinarymechanical type gramophones with soundboxes. Moreover, the actual process ofrecording is not continual, as happens inbroadcasting, and a defective recordingcan easily be re -made should a faultdevelop.

Three TypesThere are three types of condenser micro-

phone. The "high -sensitivity," the '" low -sensitivity" and the " H.F. " type. Thehigh -sensitivity type, already mentioned,has a slightly slackened diaphragm whichintroduces a resonance in the neighbourhoodof 6,000 cycles. The low -sensitivity typehas a fully tightened diaphragm and a veryeven response curve; it does however,necessitate additional stages of amplifica-tion. The third type, the "H.F.," uses anentirely different type of circuit, in whichthe, variation of the condenser varies theoutput of a valve oscillating circuit.

The B.R.C. TypeThe B.B.C. has adopted the e high -sensi-

tivity type of condenser microphone andhas incorporated in it the side of a six-inchcube box holding the first stage of amplifi-cation. The characteristic of the micro-phone has been " cooked " somewhat," andclosely resembles that of the Reisz, theAmplion and other high-grade carbonmicrophones-minus the hiss !

Whether or not this latest edition of thecondenser Microphone will become standardhas not yet been decided. But the tests andmaintenance trials have been " passed "triumphantly, and there is a great likelihoodthat the good old Reisz microphone willgradually be replaced in all stations by it,

Ct

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50 FREQUENCY 5:000 /06:0 -

Fig. 2. Condenser Microphone Curves

The outside broadcasts will probably stillbe " taken " on carbon microphones, owingto the sensitivity of the condenser type toelectrical interference caused by fans,electric -light switch sparks and the like.

Alessandro Banfi, chief engineer of theItalian Broadcasting Company recentlyarrived in America to purchase a 50 -kilo-watt broadcasting transmitter.

MAY 18, 1929 05 Catateur WireL2.s5

The turntable is driven byan electric motor and athree -valve combined dual -

AN amplifier for the reproduction ofgramophone records which is known

to have a good characteristic is a very usefulpiece of apparatus, and the instrumentdescribed herewith was constructed some

The Amplifier is of simple construction

time ago with the object of providing asimple amplifier capable of giving a highoverall amplification with- a satisfactoryresponse curve.

The uses of this amplifier are not limited,of course, to gramophone reproduction. Ithas been shown herewith coupled to anelectric motor and B.T.H pick-up-a com-plete gramophone reproducing equipment.The amplifier, however, may be used forvarious other purposes. For example asimple microphone connected through asuitable step-up transformer to the gridof the first valve will enable the smallestsounds to be magnified up to very goodloud -speaker strength. Finally, the amplifiercan easily be used if desired, for broadcastpurposes, either as it stands or with someslight modification. In either case thecharacteristics of the amplifier, ranging asthey do from 5o to 8,000 cycles, are ofconsiderable value.

The amplifier is unconventional in design.It has often been considered that for good -quality reproduction, resistance coupling isessential. I have on several occasionspointed out that this is not necessarily thecase and the present amplifier is an instanceof an arrangement giving the desiredresults without any resistance coupling at

By J. H. REYNER, B.Sc., A.M.I.E.E.

all. The advantage of the arrangement isthat a much greater amplification can beobtained than would otherwise be the case,while it will be seen from the response curve

(Fig. r) that the amplificaltion is uniform over a verywide range of frequencies,and does not fall off at highfrequencies as a resistanceamplifier is apt to do. Theactual amplificatiori is of theorder of 800, whereas with aresistance amplifier thefigure would be somethingunder 200.

The circuit of the ampli-fier is as shown by Fig. 2.The first valve is followedby a dual -impedance couplerleading to the second valve.In the anode circuit here wehave a 4: r Marconiphone

transformer, feeding the final super -powervalve. A choke -output filter is used notonly in the, interests of the loud -speakerbut also to ensure perfect quality. If anydifficulty is experienced in obtainingMarconiphone Ideal transformer, a Pyetransformer may be used.

It will be noticed that the feed to eachof the first two anodecircuits is obtainedthrough a resistancewith a 2-microfarad by-pass condenser. Thisabsolutely avoids allbattery coupling andit means that thisamplifier can be used onan ordinary dry batteryprovided it is capable ofsupplying the currentwhich is of the order of

milliamps.Points of particular

interest are the in -elusion of a high -fre-quency filter consistingof an H.F..choke and a.0003 by-pass condenserimmediately followingthe first valve, and a

Recommended10/ame Con/rd

_MAW/MVOr-

-C%oke!

I

H.L. -12/0

impedance and transformer -coupled amplifier is used to

amplify the pick-up current

1/4-megohm stopper in the grid circuit ofthe second valve. Since the amplifier isto be used, in many cases, without anyhigh -frequency stages in front of it theinclusion of these components might appear

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Fig. 1. The Response Curve of the Amplifier

to be unnecessary but practical experienceshows that this is not the case. There is anextraordinary amount of high -frequencyenergy in the most unlikely circuits andthis is likely to cause troublesome distor-tion which is very difficult to detect. Inorder to be on the safe side, adequatefiltering arrangements have been insertedand this 'results in the amplifier beingthoroughly satisfactory under all conditions.

Components Required for AmplifierThree valve holders (Formo).H.F. choke (Wearite).

/1/2i/ a6:-2 68-1..71/ /5V

Fig. 2. The Circuit of the Amplifier

6.8-+

ein,,,,follr Wirt:L.15 706 MAY 18 1929

MAKING AN ALL -ELECTRIC GRAMOPHONE (Continued from preceding page)Wire -wound anode resistance ioo,000

ohms (R.I. and Varley).Wire -wound anode resistance, to,000

ohms (R.I. and Varley).Two fixed condensers, i-mid. each

(T.C.C.).

Under side of Gramophone turntable showingG.E.C. Electric Gramophone Motor

One dual -impedance coupling unit(Igranic)..

One L.F. transformer (MarconiphoneIdeal, 4 to c ratio).

One output filter unit (Wearite).Six terminals, marked: L.S. , _L.5. -,

L.T.+, L.T. H.T. , H.T. -Terminal strips, 2 in. by 2 in. and 4 in.

by 2 in..0003 rnfd. fixed condenser (T.C.C.)..25-megohm grid leak (Dubilier).Grid bias battery clips (Bulgin).Glazite wire for wiring. Baseboard.Let us pew consider the operation of the

amplifier. How is it that we can obtain asubstantially straight line characteristicwith such apparatus?The answer is verysimple. A dual -im-pedance coupler hasa curious responsecharacteristic. I tamplifies the high -frequencies exceed-ingly well and

- usually with a slight-ly rising character-istic. Towards thelow frequencies,there is a tendencyto fall off, but thisfall is arrested by aresonance effectwhich results in ahump in the charac-teristic as illustratedin Fig. 3a. The characteristic of a trans-former on the other hand tends to fall off atthe bottom and top ends of the scale. Thecut-off at the top we do not mind, providedit is above a certain frequency. In fact, itis beneficial for it tends to eliminate higherfrequency disturbances which we do not

BLUEPRINT/rA.W /87

require. The cut-off in the bass, however,usually occurs somewhat early and here theresonance effect in the dual impedancecoupler is of distinct assistance.

The net effect is that thetwo curves addedtogether give a tolerably straight linecharacteristic as indi-cated in Fig. 3c. Thisis the type of character-istic actually obtainedon the amplifier and thecurve in Fig. 3 showsa response curve takenat the Furzehill Labor-atories on the particularamplifier being des-cribed. It will be seento be of the same gen-eral form and it main-tains its amplificationfrom 5o up to 8,000cycles. The amplifica-tion is tolerably uniformwith a rise towards thehigher frequencies which is very valuable inoff -setting the loss of high notes inherent inthe average loud -speaker and the averagepick-up.

01,14/NPEORNCE TRRNSFORMEil COMBINEDCION4KTER/S77C

Fig. 3. Showing how the combination of twocharacteristics gives uniform responses

If, on the other hand, one is using thisamplifier with either a pick-up or a loud-speaker which does reproduce the higherfrequencies effectively, then a certainshrillness will be heard. This may easily

Incidentally the amplifier will give areally good test of various forms of pick-up. If the loud -speaker is a good one asregards the higher frequencies, then a goodpick-up used with this amplifier willdevelop a distinct scratch. A poorer pick-up

A plan view of the Amplifier

not having such a good high -frequencyresponse will not show any scratch simplybecause the pick-up cannot reproduce _

frequencies above 2,000 or 3,000 cycles persecond. As I have pointed out in a previousarticle, it is much more desirable to utilisea pick-up which will supply the scratch andthe various higher harmonics of the musicat the same time. The scratch may bethen minimised by inserting a scratchfilter which just cuts out sufficient of thenoise to render the reproduction pleasant.The complete elimination of scratch is notdesirable for it carries with it the elimina-tion of naturalness. Before any experimentsin this direction can be conducted, it isessential to have -an amplifier capable ofreally reproducing the higher frequencies

and the present in-strument complieswith these condi-tions.

One final pointEboniteifixr may be mentioned

regarding volume control.The most satisfactorymethod of volume control isto connect a variable resis-tance, such as a volume -control Clarostat, across theprimary of the dual impe-dance coupler. This willenable the volume to be cutclown without any loss ofquality.

Recommended valves are :First Stage.-DEL2ro (Mar-

coni or Osram), LF210(Ediswan), 2roLF (Cossor), G. P.2 o(B.T.H.).

Second Stage. -220P (Cossor), DEF2 5(Marconi or Osram), LF2 x5 (B.T.H.),PM2 (Mullard).

Third Sice.-DEP24o (Marconi or Osram),P22"; (B.T.H.), PM252 (Mullard).

CHOKEOUTPUT UNIT

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P220VALVE

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NECROME

"DUALIMPEDANCECOUPLINGUNIT

BASEBOARD 174. X 9"

Blueprint available, price 1/ -

be obviated by connecting a condenseracross the pick-up itself and adjusting thevalue of this until the shrillness is cut off.Alternatively, the use of a scratch filtercutting off about 4,000 or 5,000 cycles persecond may be resorted to as has alreadybeen described.

9/PVT

MAY 18 1929

AR!707

ILAYERS_._

entatelir Wwele

WO

4n account of some Recent Researches made by Prof. E. V. Appleton on theLocation of the Heaviside Layer

THEhas awarded the LiebmannInstitute of ElectricalHE American

Memorial Prize for the current year toProfessor E. V. Appleton, F.R.S., in recog-nition of his recent work on the Heavisidelayer. The prize is given each year inrespect of the most important contributionmade to radio science during the precedingtwelve months.

Professor Appleton is Wheatstone Pro-fessor of. Physics at King's College, London,and has been engaged for many years in thestudy of the electrical properties of theupper atmosphere. He was, in fact, amongstthe first to produce acceptable evidence ofthe nature and location of that mysteriousregion known as the Heaviside layer.

A Double LayerIn the course of a series of experiments

designed to measure the actual height ofthe layer above ground, Professor Appletondiscovered the existence of a second layerlocated high above the first. Systematicmeasurements have placed the mean heightof the first layer at 98 kilometres, and that'of the second at 226 kilometres. Theseresults have recently been verified byindependent observations carried out inAmerica.

It has been known for some time that theoutermost parts of the earth's atmosphereare occupied by a zone of ionised air whichacts as a barrier to all wireless waves longerthan, say, 15 metres. If this were not so,long-distance reception would be prac-tically impossible.

Wireless waves tend to travel in astraight line, in just the same way as a ray'of light. Since the surface of the earthis curved, it would clearly be impossible, ifthe straight-line law held good, to transmitmessages through the ether for any con-.siderable distance. After a comparativelyshort travel the waves would leave theearth's surface at a tangent and be lostamidst the stars.

Space Waves and Ground WavesThe problem is not, however, quite so

simple as appears at first sight. In practiceit is found that the energy radiated froman ordinary transmitting aerial can bedivided into two components. There is,

By MORTON BARRfirst, an earth -bound wave which appearsto be linked in some peculiar fashion to theground, in much the same way as a high -frequency current is localised around aconducting wire.

Next there is the space -wave component,which travels upwards from the transmit-ting aerial at an angle to the ground. If itwere not for the existence of the Heavisidelayer this component would never reach adistant receiving station.

The relative -proportion in which space -wave and earth -bound components areradiated in any given case depends in partupon the type of aerial used and in partupon the wavelength employed.

Generally speaking, the shorter the work-ing wavelength, the greater is the propor-tion of space -wave energy present, and viceversa. Again, a very high proportion ofspace -wave energy can be radiated byusing a flat-topped aerial. On the otherhand the radiation from a vertical groundedwire is found to be largely earth bound.

Measuring the Angle of theReflected RayIn attempting to measure the elevation

of the Heaviside layer above the surface ofthe earth two methods are available. Thefirst depends upon the assumption that theangle made by the signal wave, as it meetsthe layer, is the same as that at which thereflected ray leaves the layer.

The second method is based upon thefact that the space -wave must travel over agreater distance to reach .a given receivingstation than the direct or earth -boundcomponent. Actually it traverses two sidesof a triangle, the base of the triangle beingthe track of the earth -bound wave.

In the first method a frame or loop aerialis used to measure the angle at which thedown -coming ray from the Heaviside layerreaches the ground.

It is well known that maximum recep-tion on a frame aerial occurs when the planeof t'he aerial points towards the source ofthe wave. Another way of stating this factis that the frame aerial responds solely tothe magnetic flux of the travelling wave.

This directional effect is generally appliedto the earth -bound wave only. In practice,when the frame is pointing towards a

transmitting station, the magnetic fluxthreading through the windings is a maxi-mum, because the magnetic field vibratesat right angles to the actual direction of thewave -front as a whole.

This action holds good equally in the

Prof. E. V. Appleton, F.R.S.

case where the received wave is travellingat an angle to the earth's surface. Accord-ingly, by using a frame aerial arranged tobe swivelled about a horizontal plane, it ispossible to ascertain the exact angle atwhich the space wave reaches the earthafter reflection from the Heaviside layer.

Once this angle is known, it is merely amatter of triangulation to determine therequired height of the point of reflection,since the distance between the transmitterand, receiver has previously been measured.

The second method is somewhat morecomplicated in practice, though it iscapable of giving more accurate results. Itis known as the " group -retardation "method, and as previously stated, dependsupon the difference in effective lengthbetween the path taken by the direct andreflected space waves respectively.

As a matter of fact, this difference in the(Concluded in third column of next page)

entakur Wirdizsi 708 MAY 18, 1929

111

For the Newcomer to Wireless: GENERATING II

ELECTRICITY II

COMEBODY told me the other dayL.; that it was quite wrong to speakabout a battery generating electricity.Surely that is not so since it obviouslyproduces current.

It would be just as correct really tosay that an electric fan generates air.

I don't see that. Of course, the fandoes not create air. It makes a draughtby setting air in motion. .

Exactly. The fan gives rise to a with a force billions of times greatercurrent of air and the battery produces than gravity; the latter rush through thea current of electricity by setting condueting path-and theft you have aelectrons in motion. ' stream of electrons which forms a current.

An electric current is a stream of Can you tell me roughly what theelectrons isn't it ? - chemical action inside the battery is ?

Yes; electrons are present every- . We will take the Leclanche cell,where and in everything. It is only which is one of the simplest. You knowwhen we cause them to move ina definite . what the electrolyte consists of ?way that we obtain what is termed a Sal ammoniac and water.

Sal ammoniac is another name forammonium chlaride. The chlorine inthe solution proceeds to attack the zinc.

What happens then?The zinc is readily dissolved but does

not give up complete atoms.How are they incomplete?

current flow.Then what does the battery do?We may say that it acts in very

much the same way as a pump. Youcould do work by pumping water froma pond and letting it fall upon the vanesof a turbine.

Each as it passes from the metal intothe solution leaves behind some of itselectrons, In other words it passes intothe solution as a positive ion.

What is the result?Since each departing atom leaves

electrons in the zinc, the metal soon

I follow that.. But how does thebattery pump electricity?

By means of the chemical action thatgoes on inside it, a large assembly Ofelectrons is produced at the negativeterminal and an equally big company ofpositive ions at the positive.

What happens When a conducting becomes charged negatively. Thepath is provided? electrolyte, receiving huge numbers of

The positive ions attract the electrons positive ions, becomes positively charged._There is thus an excess of positive ionsin the carbon rod which serves to makecontact with the electrolyte.

Suppose that we place a conductoracross the battery terminals?

The electrons, as we have seen, rushacross to the positive terminal, neutra-lizing the positive ions. The electrolytecan now get to work again on the zinc,which it promptly does and the eatingaway of the zinc goes on so long asthere is an outside path between thebattery terminals.

Then the battery produces currentby consuming zinc ?

Yes, in the same way as a boilerproduces steam by consuming coal.

ii

is33

THE UBIQUITOUS EAVESDROPPERJottings from my Log. By JAY COOTE

WHAT in these Isles is badly termed alistener, in Germany merely a hoerer,

in France, un ilinateurdeT.S.F.(an ennoblingterm !) is officially styled in Holland, aluistervink (an eavesdropper). I plead guiltyto the last application, for at any momentof the day or evening I may be found con-nected up to my wireless receiver-eaves-dropping ! And these casual and informalcalls on foreign studios invariably result in agoodly collection of interesting items.

A Relay from the Graf ZeppelinTake, for instance, May 2, when I picked

up through Koenigswusterhausen between8.15 and 9.20 a.m. what was apparently arelay from Vienna of some cross -talk takingplace between the Ravag studio and theGerman airship Graf Zeppelin whilst thedirigible was over the Austrian capital onits trip to the Mediterranean. I twirled thedials and found that the broadcast wasbeing put out by several German trans-mitters. The roar of the airship's engineswere clearly discernible as a background tothe voice which gave a list of the notableguests on board, and time after time inorder that there should be no doubt on thesubject the announcer butted in with thecall: "Radio Wien."

This is not the first time that the Austrianhas been in touch with the famous airshipon its experimental flights. Unfortunately,

however, no notice is given of the studio'sintention to carry out this two-way com-munication.

In the French MannerAgain, on May 4, towards II p.m. after

listening to the relay by Milan of the lastact of Puccini's opera La Boherne, as per-formed at the Scala Opera House, quiteby chance I found that PTT Lyons hadswitched me over to some local sportsarena in which heavy athletic competitionswere taking place. The commentator, inthe usual French manner, waxed enthusiastover the feats performed by some of thecontestants.

A Memorable OccasionThe night of May 5 provided a "star"

entry in my log for after most stations hadsigned off, I tuned in the Belgrade trans-mission which for some hours devoted itselfto so wild a programme of music and speechthat I was prompted to ascertain the causeof this unexpected exuberance. It appearsthat accord n to the Russian calendar,Easter Sunday fell on the same day as theSpring Festival or Djurdzepski Uranak, afête dating back to heathen times when bysong and dance throughout the night thenatives greeted the rising of the sun. Iheld the broadcast well for some consider-able time-there was no other st stion on the

air-and .was thus given a true picture of aJugo-Slavian National Festival.

"ARE THERE TWO HEAVISIDELAYERS ? "

(Continued from page 707)

two paths is very largely responsible for thefading effects which are so noticeable itsordinary distance reception,

The space wave travels over a longercourse' o reach the receiving station, and istherefore out of phase with the direct wavewhen the two combine, Sometimes thephase difference is such as to neutralise thesignal, whilst at other times it increases the.signal strength.

By suitably choosing the distance be-tween the transmitting and receivingstations, it is possible, first, to arrange thatthe average strength of signal due to theearth -bound component is equal to that dueto the reflected space wave.

Next, by adjusting the transmitted way e -length the space wave is made to arrive inphase with the earth -bound wave. A slightfurther periodical variation in frequency isthen superposed so as to give rise to a beateffect in the phones, from which the actualpath of the space wave and, therefore, theheight of the Heaviside layer can be calcu-lated.

MAY 18, 1929 709

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Here is the Blue Spot Metal Chassis, completewith cone in position ready for affixing theunit-simplicity itself-and takes five minutesto assemble.

To bolt the chassis to a baffle board, whichyour dealer can supply cut to size, or toa cabinet of your own choice completes aninexpensive speaker giving results little short,of amazing.

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Mention of "Amateur Wireless" to Advertisers will Ensure Prompt Attention

emattuswvaT

*PORTABLES*Choosing,

Buying,

Building &

Operating!

710 MAY 18, 1929

Do you know five good reasonswhy you should read the May" Wireless Magazine"?

It contains an extra 16 -page supple-ment for portable -set buyers.

if There are 45 different featuresappealing to every radio interest

if All the details a set -buyer needs toknow of over 100 portables.More than 200 illustrations makeit the brightest radio journal.

g Descriptions and full particulars aregiven of four home -constructor sets.

THESE ARE SOME OF THE CONTENTSYOU WILL ENJOY READING:-

PORTABLESGetting the Best from a

Modern Portable. ByD. Sisson Relph (AssistantEditor).

How to Choose, Buy, andOperate Your Portable. Six-teen -page Supplement, withDetails of over too Sets.

The Wayfarer. How to Builda Five -valve Super -het. ByJ. H. Reyner, B.Sc.,A.M.I.E.E. (TechnicalEditor).

How I Should Design aPortable. By W. James(Research Consultant).

CONSTRUCTIONALThe Twinflex. A Modern

Two -valve Reflex withoutCrystal Detector.

The Dominions Four. Con-verting it to a Short-waveSuper -het.

Building Your Own Gramo-phone.

The At --home Three. A Dual -range Set Complete withValves, Batteries, and Loud-speaker for LIT.

Planning Your Aerial. ByE. H. Chapman, M.A.,D.Sc.

GENERALHow Will Broadcasting Affect

the General Election? ByB.B.C. Officials.

Do Your Pets Like Radio?In Tune with the Trade !Leaves from a Listener's Log.

By Jay Coote.The Phantom Transmitter.

A Complete Radio Detec-tive Story.

EVERY READERCAN GET A FULL-SIZE BLUEPRINTOF ANY RECEIVERFOR HALF-PRICEBY USING THESPECIAL COUPONON PAGE iii OF

THE COVER.

Russia's Revolutionary Radio.By J. Godchaux Abrahams.

The Inevitable Radio-in theU.S.A.

Japan Has the Most PowerfulStation.

A Countryman's Diary.How the Law Acts When

Your Aerial Collapses.

Speeding News by Air-andRadio, Too !

Wavelengths of the EuropeanStations.

Under My Aerial. Halyard'sChat on the Month'sTopics.

The Music Listener. By C.Whitaker -Wilson.

Broadcast Music of the Month.By Studius.

The Best Dance Records. ByH. T. Barnett.

TECHNICALValves to Use in Your Set.What are Alternating Cur-

rents? Amp and ProfessorMegohm Discuss SomeFundamentals.

Curing Threshold Howl.Decorate Your Linen Loud-

speaker !Is Your Turntable True?Our Sets ! Useful Opinions

from Readers.Noisy Electric Drives.The Horse -power of a Kilo-

watt.Novelties and New Appar-

atus Tested.Reaction-A Mixed Business.Speed Traps for Records.Reference Sheets. Compiled

by J. H. Reyner, B.Sc.,A.M.I.E.E.

You must buy a copy fromyour newsagent TO - DAY 1J.

711

KlaveltAe/t

mum W" et

Condenser MicrophonesTHE long reign of the Reisz microphone

at B.B.C. stations may 'shortly end.The B.B.C. research ,department has been"playing about" for several years withvarious types of condenser microphone,but it was not until a couple of monthsago that a type was evolved which ful-filled the requirements of broadcasting. Agood condenser microphone has an idealresponse to the musical frequencies, ispractically blast -proof, and has no back-ground noise. It does, 'however, sufferfrom the great disadvantage that it has tobe very close to the first stage of valveamplification, gives crackling noises whenit becomes damp, and picks up electricalinterference, such as the spark made whenan electric -light switch is turned off.

Gramophone RecordingFrom time to time experimental con-

denser microphones were tried out on theLondon transmission, but the percentageof breakdowns due to unwanted " crackles "was high, and arrangements had to befixed up so that quick change-overs couldbe made to the Reisz microphones. Broad-casting goes on continuously and suchbreakdowns could not be tolerated. Ingramophone recording, however, the con-denser microphone has reigned supremefor some time. The slightly "metallic"brilliance of a high -sensitive condensermicrophone gave very fine results onrecords, 'and if any crackles or othertroubles developed a recording could beeasily scrapped and another made. Con-denser microphones are also used largelyin the production of talking films, thoughit is a significant fact that for " topicals "the high -quality carbon type of microphoneis frequently used. I noticed that thePathe Gazette people used an Amplionmicrophone of the carbon type for makingthe sound film of the Cup Tie final atWembley. -

Killing the CracklesMost of the troubles the B.B.C. has

had with condenser microphones have beenin the small amplifier which has had to bepart and parcel of the microphone itself.One of the last developments of CaptainA. G. D. West before leaving the B.B.C.was the design of a special condensermicrophone amplifier to overcome all thesetroubles. A great many of the musicaltransmissions from 2L0 during the lastsix weeks have been made with condensermicrophones in the studios, and so far-touch wood-there have been no"troubles." Do you notice any differencein the quality? If you do, you're wrong!

The characteristic of the B.B.C.'s latestcondenser microphone is practically thesame as that of the Reisz. The advantageis in the absence of background noise, suchas that ordinarily made by any microphoneof the carbon type, and the freedom from" blasting " effects on loud passages ofmusic.

Moving CoilsThere are still a few B.B.C. stations

which use the old magnetophone micro-phones, in which a moving -coil is sus-pended in cotton wool in the field of astrong electro-magnet. Round -Sykes micro-phones, as they were called, gave verypleasing results on the horn loud -speakersof three or four years ago. Indeed, theygive finer quality reproduction on hornloud -speakers than the latest types ofcarbon or condenser microphones, except-ing when horns of the exponential type areused. Judged on the latest types ofmoving -coil or cone loud -speakers, thequality from the old magnetophone micro-phone lacked bass and " body."

Resistance CapacityMy remarks on the relative merits of

resistance -capacity and transformer coup-ling a few weeks ago inspired a Manchesterreader to send a most interesting letter ofcomment in which he strongly advocatedthe suppression of resistance capacity notonly in our receivers, but in the B.B.C.amplifiers ! The B.B.C., as you possiblyknow, makes great use of resistance coup-ling. This reader points out that there is aloss of higher frequencies when highmagnification valves, resistances, and leaksare used, and that the B.B.C. must inevit-ably have a great deal of grid -currenttrouble with this type of coupling. I agreethat high value resistances in a resistance -coupled amplifier are not good, owing tothe fact that the capacity of the valveitself then becomes an appreciable factorand higher frequencies are lost. The B.B.C.,however, uses low value resistances and lowmagnification valves, and when theamplifiers are fed from H.T. accumulatorsthe response curve is dead straight from5o to ro,000 cycles, even when five or sixstages of amplification are employed IThere are ten or twelve stages of amplifica-tion between microphone and transmitter,and the overall curve is practically straight.The deviation from the straight and narrowpath, slight though it is, is due to thenecessity of using input and output trans-formers on the long lines between studioand control -room and control -room andtransmitter. This is a big score for resist-ance -capacity coupling 1

Grid CurrentIn regard to the "blasting" on B.B.C.

amplifiers, this is largely taken care of bycareful design. The magnification andgrid -swing of each stage, is carefully con-sidered, and the design of the amplifyingchain is such that the first stage to runinto grid current is that of the modulatorvalves on the transmitter. A "slide -back"meter gives the controlling engineer a"remote reading" of the grid -current meterin the modulator -valve grid circuits on thetransmitter, and this can be adjusted toindicate the maximum modulation withouttransmitter "blast." The blasting effectsthat this correspondent has heard mayhave been caused on the transmitter, butI think the microphone, particularly if ofthe carbon type, is much more likely tohave been the "guilty party."

Mains TroublesHowever, when resistance -capacity

amplifiers have to be supplied with H.T.from dry batteries or mains "eliminators,"the problem takes on a different aspectL.F. reaction, coupling, and even motor -boating may occur. And when the amplifieris connected with a detector and a fewH.F. stages which are sharply tuned, itmay be a disadvantage that the responsecurve is dead, straight ! Such a receiver willrequire an amplifier which has a risingcharacteristid above 5,000 cycles, in orderthat the cut-off introduced by sharplytuned H.F. circuits shall be neutralised,and this characteristic may be obtainedby using good transformers.

Sir John Aird and TelevisionIn an interview granted to a Canadian

newspaper, Sir John Aird, Chairman of theCanadian Royal Commission on RadioInvestigation, who returned to Canadarecently with other members after aninvestigation of radio in Europe, statedthat he was particularly impressed withwireless conditions in the mothercountry. He declared that, in his opinion,Great Britain is ahead in Europe so far aswireless is concerned, with Germany a goodsecond. What impressed me most, though,was Sir John Aird's conviction that it wasonly a matter of a very short time beforetelevision would be quite common in thiscountry. He, with other members of theRoyal Commission, had witnessed a demon-stration of the Baird Co.'s system, andthey were all mast emphatic in theirremarks concerning the progress made.In the opinion of Sir John, we haveadvanced much farther than the Americansin television.

mats ur 712 MAY 18, 1929

On Your Wavelength ! (continued) A Curious Trouble

I came across an interesting snag theother day which I myself, at any rate, hadnever encountered before. I was testinga portable receiver and, as one often doesin hook-ups, I had arranged the panel withthe various condensers and other controlsthereon separately from the rest of theworks, the two being connected by flexibleleads. In order to mount the panel in avertical position, I picked up an cid2-microfarad condenser and placed thisunder the variabh condenser on the panel,this serving to support the whele, arrange-ment practically vertical, so that I couldoperate it without difficulty and stillobtain access to the various connections incase I wished to alter any of them.

The receiver worked fairly well, but Iwas troubled fcr a long time with anintermittent contact which I could notfind. Sundry hangings of the set con-vinced me that there was some sort ofloose contact effect, for any sudden jarwould set up a horrible crackle whichevery wireless enthusiast knows; yet, tryas I would, I could not locate the source ofthe trouble. I went over every connectioncarefully and re -made the greater portionof these, but still this annoying troubleremained. In exasperation I even changedthe L.F. transformers, for, although I hadnever come across a breakdown in thewindings of an L.F. transformer so severeas to give a crackle of this nature, yet Iwas by this time at my wits' end to tracethe difficulty. Rather as I expected, how-ever, the transformers were not at fault,and I was left with the curious position ofhaving tested or changed everything in theset and still apparently having a loosecontact.

Almost HopelessAt this stage the bright and happy reader

says : " Ah, of course, the poor mutt new rtroubled to change his loud -speaker !" Asit happens, however, gentle reader, youare completely and utterly wrong, becausethis was about the first thing I did change,and I can assure you that this was noordinary fault that was causing the trouble.I had practically decided to take the wholething to pieces, aid put it on one side forthis purpose. Almost as a last resort Iswitched on again and found, to myamazement, that the crackle was no longerpresent, although the leads were now quitejumbled up. To cut a long story short, Ifound that in moving the apparatus I wasKO longer supporting the variable con-denser on the 2-microfarad condenser, andthis proved to be the solution to the wholeproblem.

An Unusual CauseWhether the 2-microfarad condenser was

faulty or not I do not know. It did notshow any fault on test and was a perfectly

well-behaved condenser, but it was in athin moulded- case, and apparently thevarying pressure on this case producedsome effect on the foil inside. At any rate,putting the 2-microfarad condenser underthe panel condenser once again, and usingit as a support, immediately caused thecrackle to recur, and I can only put itdown to' some curious capacity to earth.:The 2-microfarad condens'er, -I would say,NN, -as not in circuit at all and was -beingused merely as a support. The moral is :Do not use 2-microfarad condensers orother objects of this nature as supports forelectrical apparatus unless' you wish tohave a harassing time.

Do You Find This?For some little time past I have been

wondering why it is that I do not havenearly the same success with distant sta-tions whose wavelengths lie between about425 and 46o metres as in other parts of theordinary broadcast band. On good nightstransmissions come roaring in on the lowerwavelengths and on those above, but inthis particular patch I always seem toneed much more' reaction to get decentstrength out of it. I used to think that itwas due to a dip in the characteristic of achoke or something of that kind, butexperiments with different breeds of chokeall produce much the same result. To mysurprise I found, on discussing the matterwith a friend the other day, that he hasexactly the same difficulty with just thesame small band of wavelengths. His cir-cuit is quite different from mine and hislocality is much better from a receptionpoint of view than is mine. Do any readersfind the same partial hole in their tuningthat we do, and can anybody offer anexplanation of it?

Good DX ConditionsExcellent conditions for wireless recep-

tion still continue. Atmospherics rarelycause any bother; fading is seldom notice-able except, maybe, for a short time atdusk; and signal strength is extraordinarilygood. I have been quite surprised to findwhat a number of foreign stations thereare nowaday; on the medium band 'whichcan be quite well received in daylight. Asa rule, the approach of summer meansthat the DX man's evening must beginlater and later, but this year a trip abroadis often productive of good results at quitean early hour. The four outstandingforeign stations at the present time areTurin, Nuremburg, Ho'erby, and Cologne.

Next Week :"BRITAIN'S FAVOURITE TWO"

1929 MODEL

The queer thing is that long ranges donot always seem to depend upon the powerbehind the transmitter. Nuremburg, forinstance, is only 4 kilewatts, though hecomes in; as a rule, even more stronglythan Hoerby with ro kilowatts, the rangesof the two being very much the same. The7 -kilowatt Turin is sometimes as strong aseither of them. But the wonder of thebroadcast band is Kaiserslautern, who israted at only point seven kilowatt, butcomes in as strongly as if he had the fullseven without the point. Paris P.T.T. isanother smallish station with a big voice.

More and MoreBerlin Witzleben is now 'sending pic-

tures on most if not all evenings of theweek as a regular part of his programmes,the transmission time being often between7 and 8 p.m. Except on Sunday nights,many of us have rather a business toreceive Witzleben, owing to the wipe-outof 5GB. But it is worth while noting thatthe Berlin station's programmes are oftenrelayed by other big Germans. The othernight, when Breslau was taking his pro-gramme, I found that both he and Glei-witz were sending pictures, conditionsbeing such that excellent reception waspossible. Nuremburg has also been Fulto-graphing, and many other of the Germanstations will be added to the lists veryshortly now. I sincerely hope that theB.B.C. will soon make pictures a regularpart of its programmes.

Earthing SwitchesThe recent instance of the destruction

of a wireless set by lightning rather tendsto emphasise what I have always saidabout the earthing switch. In this par-ticular case the set was supposed to beearthed, but the switch seems to havebeen of very *small size and to have beeninstalled inside the house. Now, the pro-per place for the earthing switch is unques-tionably out of doors, for when you cometo think of it you don't want deliberatelyto conduct currents at a million volts orso into your abode. Further, it should beremembered that the single -pole double -throw switch so often used is practicallyuseless. With this the earth is left con-nected to the receiving set and a shunt pathis provided from the aerial to earth. Ahigh voltage current may jump the gap tothe aerial connection, playing havoc withthe receiving gear. The earthing switchshould certainly be of the double -polechange -over type, cutting the receiving setclean out and providing a straight -throughpath to earth. Better still, don't use aswitch at all, but disconnect both aerial andearth leads from their terminals outside thewindow, hook them together and let themswing away from the house.

THERMION.

MAY 18, 1929 713 Indent Wirele5

The second of a new series ofarticles which will appear fromtime to time from the pen ofour Technical Editor, indicatingsome of the methods employed

DESPITE the increasing use of electric -light mains for supplying current to

wireless receivers, the vast majority of setsstill have to make use of batteries for theirpower. The low-tension, of course, can beobtained from an accumulator which iscapable of being re -charged, but the high-tension supply is more conveniently ob-tained from dry batteries. In certaininstances wet batteries or high-tensionaccumulators may be used, but there is(and will be for some considerable period)a large demand for dry batteries of thezinc -carbon type.

Length of LifeFor some time past, AMATEUR WIRELESS

test reports have quoted the approximatelife of the batteries in milliampere hours.The actual life in practice depends uponthe conditions under which the battery isused. One of the special features of thezinc -carbon battery having an electrolyteof sal -ammoniac or some similar salt is thatit is capable of considerable recuperation.The effect of discharging the battery isthat the chemicals are used up and inconsequence the voltage on the batteryfalls. The battery, however, contains cer-tain other chemicals which tend to arrestthe fall of the voltage, and it is really onlyby virtue of these chemicals that we areable to obtain practicable results.

These chemicals are working to maximumeffect when the battery is in use. When thebattery is taken off discharge and allowedto rest, however, the "depolarising"chemicals continue their action and pro-ceed to some extent to repair the damagewhich has been done by taking the dis-charge from the cells. They cannot com-pletely recover the lost ground, but thecell certainly is in a fresher condition aftera period of recuperation than it was whenit was switched off load.

If the battery is kept on a continuousdischarge, therefore, it will lose its effectivevoltage more rapidly than if it is dischargedfor short periods and allowed to recuperate.For this reason batteries are sometimestested by being placed on discharge for acertain number of houri each day andallowed to recuperate for the remainder of

the time. This certainly approximates topractical conditions, but it is impossible tosay how long a battery will actually beused in practice, and after due considera-tion it appears better to discharge thebattery continuously and to make allow-ance for the increased plerformance whichwill be obtained if the battery is only usedintermittently.

Method of TestingThe method used in making tests, there-

fore, is to place the battery on dischargethrough a constant resistance. This resist-ance again is a somewhat arbitrary value,for a peculiarity of dry cells is that themilliampere -hours life from a batterydecreases as the current increases. If wedouble the current which we take from abattery we might reasonably expect it tolast half as long. Actually it will only lastsomething between .3 and .4 times as long,this effect being due to the fact that thedepolarising action has not had time tocome into full operation. Conversely, ifwe discharge the battery at a very slowrate we can obtain a performance on con-tinuous discharge which is very nearlyequivalent to that obtained by dischargingit at a normal rate for, say, five hours per

HAVE YOU NOTICED-what an untidy job, unlessthe constructor is experienced, isfrequently made over soldering ?And when this is the case, thefutility of taking the trouble tosolder, when the tag to whichthe wire is soldered is itself heldunder a nut ? Thus, as far asgood electrical contact goes, thewire held directly under the nutor terminal head is equally satis-factory. These remarks do not,of course, apply when the tag isan elongation of the part itself,when, naturally, the advan-tages of soldering are self -apparent.

in the testing of manufac-turers' components and appar-

atus. The subject of this articleis the testing of high-tensionbatteries.

day and leaying it to recuperate for theremaining nineteen.

In making a practical test, therefore, acompromise is adopted. Take, for example,the average single -capacity size of drybattery. This is rated to give about7 milliamps economical discharge. Weplace this on test, therefore, connectedacross a resistance so adjusted as to draw7 milliamps from the battery. As thevoltage on the battery falls the currentalso falls, since the resistance has remainedconstant, and consequently the current,instead of being fixed at 7 milliamps,gradually falls away. This process is con-tinued until the voltage on the battery hasfallen to one-half of its initial value. Thecurrent, then, has also fallen by one-half,and at this point the battery is consideredto be exhausted. This method of testinggives slightly better results than would beobtained if the discharge was maintainedconstant at the full 7 milliamps.

Milliampere HoursThe actual milliampere hours given out

by the battery-that is to say, the productof the current and the time during whictthe current is taken-is obtained by asimple calculation. The current is obvi-ously not 7 milliamps the whole of the dis-charge, nor is it 3 4 milliamps, the formervalue being too high and the latter valuetoo small. What we require is the averageof these two values, and a little thoughtwill show that this is three-quarters of theinitial discharge rate. We obtain themilliampere -hour consumption, therefore,by multiplying the initial discharge rateby three-quarters and multiplying this bythe number of hours continuous dischargeobtained from the battery before itsvoltage fell to one-half.

Practical experiments show that thisfigure should be in the neighbourhood ofi,000 for an ordinary dry battery of thesingle -capacity type. Double -capacity andtreble -capacity types should give approxi-mately 2,000 and 3,000 milliampere hours.In the case of the larger sizes of battery,of course, the discharge rate is larger,since these batteries are intended to give

(Concluded in third column of next page)

illftlPivr WireLT

IN a recent issue; Jay Coote, in his1 feature " Jottings from My Log,"spoke about the new Belgrade station.This was officially opened on March 24last and has been transmitting almostnightly.

Whilst the tests were on, Jay Cootesearched on the, wavelength of 26o.5metres allotted to it, under that well-worn scheme, the Plan deBrussels. Theresult was, as is not altogether uncom-mon with foreigners, that Belgrade wasfound to be working just betweenAachen and Porsgrund-that isbetween 450 and 455 metres !

The call is Radio Beograd, the firstsyllable of the second word beingpronounced as the English "bay."The power approaches that of 2L0 andit is therefore interesting in that itprovides new "meat" for the DX fan.

British BuiltThe whole station has been built by

Marconi's Wireless Telegraph Co., andis, in appearance, similar to any typicalmain B.B.C. station. The fact that aBritish firm was called upon toorganise broadcasting in Belgrade issurely a tribute of which we shouldbe proud. The station itself is largeand three studios are used to provideadequate programme service. At presentthere are about 7,000 listeners withinrange and it is estimated that mostof them are valve -set users. The numbershould experience a big jump now thatBeograd is in active operation.

The type "0" transmitter, which is atBeograd, is very interesting becauseMarconi's have designed it as quite astandard job for use as a main broadcastset to serve a comparatively large area.The transmitter consists of the rectifierunit, the master oscillator, the poweroscillator or magnifier unit and, finally,

714

speech amplifiers and

The RectifierThe rectifier unit is a giant in its way,

and its -purpose is to convert ro,000 voltsA.C. to comparatively smooth D.C. Onthe I-I.F- side the master oscillator circuitis one of the outstanding features of theMarconi transmission system. Largeaccumulators supply the L.T and this isalso the case with the main oscillator andthe modulators.

It is worth while to see the way in whichpower is expended in the various circuits ofa typical transmitter, such as is at Belgrade.

the

An interior view of the main transmitting room at Radio Beograd

modulator.

MAY 18, 1929

The anode of the main oscillatingvalve has 1.5 kw., the drive oscillator

kw. and the modulator 1.5 kw. Itis rather surprising that 1.2 kw. isexpended in treating the filaments bymeans of D.C. The main oscillatorvalve takes 24 amps. filament current !

The " Q" type transmitter at Beo-grad necessitates fairly expensivegadgets, which many amateurs, andparticularly amateur transmitters,would be proud to own. Super -capacitybatteries for L.T., motor -alternatorsets, battery charging plants and so onare all included in the list of extras.

Aerial ArrangementsAt Beograd the aerial is suspended

between masts approximately 8o ft.high, which have been erected at thetop of the building. The layout iscomparatively efficient and shouldresult in an effective radiation withoutundue directional effects. Matters ofthis kind, however, are being experi-mented with in initial tests. In theopinion of many listeners in thesouth of England, Beograd is some-times being received at very nearlythe strength of Turin, and in any easequite loudly.

At present no interval signal has beendecided upon-not even the ever -popularmetronome tick -tick. This deficiency ismade up for by the fact that all announce-ments are made in four languages, namelyEnglish, French, German, and Serbian,which latter may not be recognised by manylisteners in this country.

When next making a round of the dialssee if you can log the newcomer on itspresent wavelength.

SECRETS OF THE TEST ROOM(Continued from preceding page)

a higher current, and should thus be testedunder conditions approximating to theirnormal use.

Further tests show that the same batterytested on a continuous discharge and on adischarge of an intermittent nature givesresults in the ratio of i to 1.75 approxi-mately. That is to say, a battery dis-charged under practical conditions willgive approximately 13A times the lifequoted in the actual test report. The testreport, therefore, serves firstly as a meansof comparison between different classes ofbattery. Moreover, the particular testdoes not occupy an undue length of time,whereas the intermittent discharge takessomething like a month in the ordinarycourse of events. Secondly, it serves as aguide to the life to be expected from thebattery, since the reader can easily cal-culate for himself the approximate life bymultiplying the milliampere -hour figuresgiven in the test report by 1.75 and divid-ing this by the average number of hoursuse per day. This will give the length oflife of the battery in days approximately.

MAY 18, 1929 715

WITHOU

)111111111111111111111H

y111 S, C

efi :

1111111111111l111

,A Weekly Programme Criticism by Sydney A. Moseley

AMATEURS have often written to measking how it is that when reaching

out they hear talk, talk, talk from theGerman stations.

An understanding of the local conditions,however, is very enlightening. It is not allponderous talk. The German loves tointersperse his entertainment with intro-ductions of a gently chaffing nature. Atthe tea -dances, music -halls, everywherewhere fun is to be had, you will hear anannouncer entering the'arena and seeminglygive a talk before the next item comes on,but since every sentence is followed by anoutburst of laughter from the audienceyou know very well that it is all part ofthe comedy. I daresay that if the Germanstudios had audiences as we have (ratherfoolishly, I still think), British listenerswould realise that all the talks are not asserious as they sound.

"B.M.," of Wood Green, wants to knowif I am interested in the views of "the veryyoung generation" on the Children's Hour.

"You publish the views of the BigChildren on this important question !"he writes, "so perhaps you will give a littlespace to a juvenile." Oh, certainly !

"My little daughter listens very regu-larly to that part of the day's programmedevoted to children and takes a specialinterest in the birthday greetings. But shedefinitely dislikes the repeated basso,xclamation of 'Hello, twins

"She thoroughly enjoyed a recent hourdevoted to animals at the Zoo. Stories inwhich animals appear and make realanimal noises intrigue her immensely. Ihave taken a census of opinion from otherparents and found this partiality foranimals,. quite general. She likes themusical part, but thinks the Uncles aresometimes rather 'silly.' "

My correspondent finishes up with theremark that, contrary to the generalbelief, "children are more interested inthe real thing rather than make-believe."

Don't you think the opera broadcastshave been really excellent? Surely nobodycan grumble now about not getting theirten shillings' worth 1

A correspondent has gone to great painsin order to point out that I made a mistakein saying the second issue of Gay Sparks

was by Chariot. Sorry, Mr. de Courville I

" We have now heard both StanleyBaldwin and Lloyd George on the wire-less," writes R. Sims, of Marylebone, " andit is interesting to compare the two per-sonalities from a listener's point of view.Lloyd George is easily the speaker withthe greatest wireless personality. He isentertaining and makes his presence felt.Mr. Baldwin, on the other hand, has moreof the lecturer's style and talks at us. Hewas not half as interesting as L.G."

Here is an interesting point of viewwhich ought to promote discussion.

" I am not a sturdy he-man of theNorth," writes H.B.E., of Woking, "butI like to be given what is promised me.One of your correspondents recently saidthat a good orchestra attracts the crowdwhen in competition with a band. I believethat I am right in thinking that bandmusic is just as well recognised a type aschamber music. The other day I read thatone df our foremost composers was givinghis attention to music for bands."

My correspondent maintains that we

Miss Ann Penn-and her impersonations ofNellie Wallace, Dora Maughan, Gwen Farrar

and Grade Fields

have very little of this type of music fromthe Wireless Band and that the music theydo give us is played in the manner of anorchestra, and not as, say, the ColdstreamGuards would play it. "If I am right,"he concludes, "why have an orchestracalled a military band ? "

Now and again one gets a cry of exaspera-tion from a listener who finds that his pro-tests to the B.B.C. direct are apparentlyunavailing. He then complains to AMA-TEUR WIEELESS in order that "somethingmay be done" 1

I am referring to a correspondent whodeplores the amount of time devoted totalks other than those which have a directappeal to him.

"It is no use writing to the B.B.C. aboutsuch things. I have done so frequently,but since they are a Corporation they areoff -hand and disobliging, and their soleidea of development is by the introductionof further talk, talk, talk-either by wayof debates, speeches, or robot plays.

" I begin to think the programmes arefor their own amusement in the studios.They know the cry is for music, goodmusic, and more music; but they show nodevelopment in this direction."

Although my correspondent likes thelanguage talks (because he happens to bea linguist I), he asks for an earlier timingfor talks on gardening, household, farming,and marketing.

" I think I only pay my fee for thelanguage talks and the symphony concerts;practically all the rest of the programme issheer rubbish, and I consider the fee toodear for the latter."

And I know somebody with a gardenwho would be awfully upset if the garden-ing talks were given before he could gethome from the City 1

The Italian Broadcasting Company hasauthorised the Marconi Company to pro-ceed with the manufacture of a short-wavebroadcasting transmitter for Italy. TheItalian station will to a large extent followthe design of 5SW, and will enable theItalian Broadcasting Company to carry ona broad6sting service for the Italiancolonies.

Winding the Frame AerialDETAILS of the construction of the

receiver portion of the TalismanPortable were given in last week's

issue. There remains only the frame to bewound and the receiver to be assembledin the cabinet.

Assuming that the constructor has cutthe fretwork grille, which forms a facia forthe loud -speaker, and that the frame wind-ing terminals and switch have beenmounted, the stranded frame aerial wirecan be prepared for the medium -wave-length winding.

Anchor the beginning of the winding bytying the wire in a knot around the supportnearest to the switch. Now wind on eightturns and connect the wire to one of theterminals on the three-point switch. Thewire that is left should then be connectedto one of the other terminals on the three-point switch and the short-wave windingcontinued until another seven turns have

716

A Highly SuccessfulPortable

by L. A. Chapman :Making the Frame

Aerial :Assembling :

Testing

been wound on. The wire should thenbe anchored off in the same way aswhen first started and sufficient length

left for connecting both the start andthe end of the short-wave winding to

the outer two of the three ter-minals mounted on the frettedgrille. The centre terminal isthen connected to the remain-ing terminal on the three-pointframe aerial switch.

The long -wave windingconsists of fifty-four turnsof No. 32 d.s.c. copper wire,each turn being arrangedclose to its neighbour. This

winding calls for a little care as the wire israther thin and if too much tension isapplied it will be liable to break. On theother hand if insufficient tension is appliedto the wire in winding then the whole ofthe long -wave winding will become stragglyand look untidy.

Anchor the beginning of the winding tothe support nearest to the switch in thesame way as for the medium -wave winding,

- allowing sufficient spare wire for connectionto the terminals on the grille.. Now windon the wire, leaving a space of 3/4 in. betweenthe end of the medium -wave winding andthe beginning of the long -wave winding.Put on twenty-seven turns and then doublethe wire back over itself to form a "bight"and anchor off to the support nearest tothe switch. The bight thus made should belong enough to permit making a direct con-nection to the centre terminal (s) (page 688,No. 361) of the three terminals on the grille.This being done, without breaking the wire,

The first stage in the assembly and wiring-the components on the panel

717

Hints on Tuning :

LISAAN PORTA ,

continue to wind on anothertwenty-seven turns in thesame direction as the firstsection of the winding.Anchor off the wire aroundthe support nearest to theswitch as in the first case.Both the medium -wave wind-ing and the long -wavewinding should be wound onin the one direction.

In connecting up the endsof the frame windings useextreme care in baring theends of the wire of insulation.Twist together the wireforming the beginning of themedium -wave winding andthe beginning of the long -wave winding. Connect thesetwo to the terminal marked c.The wire forming the end of themedium -wave winding and thewire forming the end of the long -wave winding should also betwisted together and these two takento the terminal marked A. See thesmall perspective drawing of the frame andswitch connection (page 688, -No. 361).

Adding the Loud -speakerIf the loud -speaker has not already been

fitted in position this should now be done.Some of the portable types of Graworspeaker are supplied for fixing flush withthe grille, whilst others require smalldistance pieces between the grille and theback edge of the speaker unit. The flush -mounting type has an extended screwedrod fitted to its reed movement.

batteries connected up.Make a final check of all con-nections before putting in thevalves and connect the flexlead to the anode terminal ofthe screen -grid valve beforeplacing the special plug intothe socket. As a final pre-caution, if you have notincluded the fuse in the con-struction of the receiver put

one in the H.T. negativelead for the first trial.

Now switch on thevalve filament switch

and turn on therheostat abouthalf -wayround. If theloud - speakerhowls then re-duce the H.T.tapping for theanode of thescreened - gridvalve. Keep

the reaction condenser set to a minimum. Ifno sound at all is heard then turn your atten-tion to the frame and H.F. coil switches. Seethat the knobs are pulled up for the medium -wavelengths and pushed down for the longwavelengths. Set the tuning condensersto the approximate adjustments for thelocal station or Daventry and bring up thereaction condenser. This should resultfirst of all in a slight rustling noise and by afurther movement a squeal. This will notcause interference with other listeners. Inconnecting up the receiver see that thecentre terminal of the frame aerial is con -

TheTalisman

Portable ready for use

nected to a point giving y2 volts negativeAfter having mounted the unit, place thediaphragm in position and carefully marks,bias on the grid -bias battery.a pencil line around the edge of the dia- With the Pertrix battery used in thephragm- on the back of the grille. Nowtake the special " felt " as supplied with thespeaker unit and gum this over the pencilline right round where the diaphragm willnormally rest. The "felt" should be soarranged that its centre is right over thepencil line first made. Seccotine will befound to be a suitable adhesive.

Bench TestBefore attempting to put the receiver

and the speaker into the cabinet thecircuit should be checked over. The partscan be laid out on the table and the

original set I find that applying the fullvoltage to the H.T. positive 4 terminal and-about go volts to H.T. positive 3 terminal,

it166 volts to H.T. positive r terminal and6o volts to H.T. positive 2 terminal thereceiver gives adequate volume with greatstability. Some variations in H.T. voltagetappings may be necessary according tothe valves in use.

Valves to UseThe valves I use are Six -Sixty 215SG,

21oHIT for the detector, 2ioLF for thefirst L.F. and 23oSP for the last L.F.Other valves I have tried have been Osram

Forty-oneStations

atLoud -speaker

Strength!

S215 for the screen -grid stage, Six -Sixty2roRC for the detector stage also Edis-wan LF2io for the detector stage, Edis-wan LF2io for the first L.F. stage andOsram DEPz4o for the last L.F. stage.The higher the impedance of the detectorvalve the greater the stability of the receiverand the smoother the reaction control, butamplification suffers a little. An H.F.valve gives good amplification and reason-able stability with ease of reaction control.An L.F. valve in the detector position givesmore amplification than the H.F. type valvebut it is inclined to be unstable.

If valves tend to sing or howl then theculprit can be found by flicking each bulbwith the finger when a pronounced " pongwill be heard.

Hints on TuningHaving satisfied yourself upon the

handling of the receiver on the localstation, now try to tune in a few of the morepowerful distant stations. If the frametuning condenser setting differs by manydegrees from the anode tuning condensersettings then try spacing apart the medium -wave frame turns to bring the condensersettings more into step.

The dials should be in step with eachother around the middle readings, thusallowing for a slight variation at, the twoends of the scale.

In the original receiver the two dialswere in step over almost the whole scale,on the medium waves, and out of step afair amount on the long waves. This is notdetrimental and cannot be avoided on thelong waves, as the inductances for eachcircuit on the long waves differ so much.

Calibrating the ReceiverThe set, when working properly, can be

placed in the cabinet. Slip all of the wander-plugs and wires through the lower part ofthe front of the cabinet and ease themthrough into the battery compartment.Before sliding the receiver down into itsown compartment slip the loud -speakerleads through from the battery compart-ment into the receiver compartment andattach the leads to the proper points. Novtake up all slack wires into the batterycompartment and ease the set into the spaceprovided for it.

The flexible battery leads should then bepulled up out of the way of the batteriesand the latter put into place. The grid -biasbatteries fit one by the side of the L.T.battery and one in front of it nearest to thereceiver compartment. This means putting

This photograph shows a front view of the completed receiver portion

r.

einaLtur Wirole.ssj 718 MAY 18, 1929

" THE TALISMAN POR.TABLE " (Continued from preceding page)

in the accumulator before the grid batteries.Arrange a length of thin but strong tapearound each of the batteries to facilitatetheir withdrawal when required. Nowconnect up all batteries as before and alsowire up to the frame aerial. Place thecover over the battery compartment andcalibrate the set according to the list ofstations received on the original set.

Practically every station given in thelist included in these pages was receivedat fair to good volume loud -speaker strength.

With the receiver in use within twomiles of the London station I consider itpossible to get about twelve alternativeprogrammes any night. I hav2 receivedRadio Paris, Hilversum, Eiffel Tower,5XX, 5GB, Brussels, Turin, Toulouse,Zeesen and, of course, 2L0, during day-light hours' at varying strengths on theloud -speaker.

41 Stations at Loud -speaker StrengthIn giving this list of stations received, I

would like to mention that the stations givenhave not been received regularly everynight or on any particular night. It hastaken nearly a month to get them all.Now that I have drawn up a rough calibra-tion curve I find that I can pick on almostany individual station and tune it in duringthe dark hours.

Tuning is not simplicity itself, as somereaders may anticipate, but by careful

This pictureshows clearly the

assembly of the combinedframe aerial and loud-

speaker

handling of the reaction condenser andjudicious use of a pocket compass readersshould have no difficulty in picking upabout thirty-five stations for home recep-tion.

Test ReportThe following stations have all been

tuned in on the loud -speaker, without theaid of phones. Fading has been experienced

with a number of the more distant stationsbut this is only in keeping with normaltypes of receiver. Those stations markedwith an asterisk have been definitelyidentified by their own announcement.

MEDIUM WAVESStation

Unidentified*Budapest

*Munich*Vienna*Brussels*Milan

Aerial Anode... 172.5 172.,. 162 161.5

... 160157

154... 150

15915515215o

For the convenience of constructors whohave not yet completed the constructionof the Talisman, we are again giving thelist of components

Ebonite panel, 14 in by 6 in. by A in. or in.(Becol, Raymond, Ebonart, Paxolin).

Two variable condensers, .000s microfarad(Ormond Midget, Utility, Formo).

Two slow-motion dials (Ormond, Utility, R.I.and Varley).

One rheostat, 15 ohms (Lissen, Igranic, G.E.C.).One variable condenser, .000z microfarad

(Cyldon Bebe, Peto-Scott).One L.T. switch (Wright 84 Weaire, Trix,

Lissen).Dual -range tuning coil (Wright & Weaire).Copper screens (Parex, Wright & Weaire, Ready

Radio).Two H.F. stoppers (Marconiphone).Safety. fuse (Bulgin, Ready Radio).Two fixed condensers, t microfarad (T.C.C.,

Dubilier, Ferranti, Lissen).One fixed condenser, S.P. type with clips,

.0003 microfarad (T.C.C.).One fixed condenser, 2 microfarad (T.C.C.,

Dubilier, Ferranti, Lissen).Four anti-microphonic valve holders (Lotus,

Wearite, Formo, Trix).One H.F. choke (McMichael, Burndept, Polar).One grid -leak holder (Ediswan, Lissen, Dubilier).One anode resistance, cartridge type, 30,000

ohms (Carborundurn, Lissen, Ediswan).One grid leak, 2 megohms (Dubilier, Lissen,

Ediswan, Mullard).Two L.P. transformers (Philips, Mullard.

Igranic, type J).Frame aerial switch, 3 -point type (Wright nd

Weaire, Bulgin, Ormond).Frame aerial wire, zoo ft. (Lewcos).Loud -speaker unit, portable type, and cone

diaphragm (Grawor).Unspillable accumulator, 2 volt (C.A.V. zN.S z

Exide W P.C. 4, Pertrix, Oldham).H.T. battery; too volts (Pertrix, Ever -Ready,

Siemens).Two grid -bias batteries, g volts each (Pertrix

Ever -Ready, Siemens).Eight wander plugs, five red, three black (Clix).Spade terminals for accumulator, one red and one

black (Clix).Glazite wire for wiring and few yards of red and

black flex (Lewcos).Cabinet of dimensions given (Carrington).Fourteen 4 B A. nuts and screws and three small

terminals.Two ounces of No.32 d.s.c. copper wire for long -

wave frame winding.Plug and socket for S.G. valve anode connection

(Clix).Station tuning chart (Bulgin).

Station*Daventry_(5GB)

Aerial Anode144 144

*Merlin 141 141.5*Lyon (PTT) 140 140

Langenburg 137.5 137

Here are the components mountedon the baseboard ready for securing

the latter to the panel*Paris (PTT)*Rome*BruneMadrid ...

*Frankfurt ...Katowice

*Dublin*Hamburg*Toulouse*Stuttgart ...*London (2L0)*Gleiwitz*Cardiff ...*Breslau*Aberdeen ...*Radio Vitus*Belfast ...*Bournemouth*TurinKaiserslautern

*Cologne ...Horby (Sweden)

*NewcastleNurnburgUnidentified

*CorkFlensburg

LONG WAVESStation Aerial Anode

Kovno (?) 152 131.5*Huizen 141 122*Radio Paris 132 113*Zeesen 122 104*Daventry (5XX) ... 112 97*Eiffel Tower rot 87Motala (?) ... . . 82 72Kalundborg (?) 48 47Hilversum ... 29 35

Tuning CoilsAs the coils for this portable are of

particularly simple design, many con-structors will doubtless prefer to maketheir own; full instructions for doing thiswith complete winding data will be givenin our next issue.

. .. 133 132.5 132 131 127 128 . 125.5 126 123 124. 121 122 119 120

114 114. ,o8 109 .

10599

robxoo

83 858, 838o $2

75 7773 76-.57o 7363 6559.5 59.557 5747 5044 48.537 3835 3521 26.516 2212 19.5

MAY 18, 1929 719 (imam, Wireigo

The

"Talisman Portable"results dependon ORMONDSuper QualityParticular attention is called tothe specification of Ormond Com-ponents for "The Talisman Port-able" Receiver as explained inlast week's issue of this journaland on page 716 of this issue. To

I

ensure the best possible resultsalways fit Ormond Components

and enjoy the utmost precision at the lowest price.THE ORMOND SMALL LOGARITHMIC CONDENSERDesigned to meet the demand for a smaller type of condenser and to give the greaterefficiency. where space is limited. Adaptable for " one -hole fixing " baseboard mounting,or alto panel mounting " for drum control.

Capacities .00013 .. 7/ 3 .00025 ... '7/6.00035 ... 7/9 .0005 .. 8/ -

THE ORMOND SMALL SLOW-MOTION DIAL

Fast enough for easy searching, slow enough forfinest tuning. Fine hair line for accurate reading.The cursor moves in the same directicn as therotation of the knob.

Silver Dial, Black Marking, Price, 3/6Black Dial, Silver Marking, Price, 3/6

Leaflets and Booklets on request.

THE ORMOND ENGINEERING CO., LTD.,Ormond House, Rosebery Ave., London, E.C.IPhone: Clerkenwell 33344-6. Grams: "Ormologiengi, Smith." Factories : Whist:in Street, andHardwick Sleet, Clerkenwell, E.C.1. Continental Agents:Pettigrew & Merriman, Ltd.," rbonos,

House," 2 and 4 Bucknall Street, New Oxford Street, London, W.C.1.

HELLESENDRY BATTERIES

Standard Capacity." Wiray" 0 -volt Grid

Bias Type 2/-" Wirin" 60 -volt B.T.

Type ... 10/6"Wirup" 99 -volt H.T.

Type ... 181-" Wisel " 108 -volt }LT.

Type ... 20/ -Treble Capacity.

" Kan " 60 -volt H.T.Type ... 19/-

" Kclup" 00 -volt B.T.Type ... 32/6

Your Ceder Sells Them.

QUIDS INVaughan rang me to -day. Sajdhe was going to buy a HellesenH.T. Battery for his set and wasproposing this time to get a"Treble" capacity instead of a"Standard.""Wise Bird," I said, "you willget three times the capacity atless than twice the cost.""I suppose," he opined, "that'sbecause Mr. Hellesen finds itmore economical to make one bigbattery while he is at it ratherthan three smaller ones.""Precisely, but there is more to itthan that. Your ' Treble' capac-ity will last you longer than everbecause you won't be running it`all out' the whole while. Youwill find your extra outlay just-ified many times over .. bye-bye:'

Supreme 1cr 27 Years.

BELLESEN DRY BATTERIES INSTRUMENTSPOLYMETi MICA te PAPER CONDENSERS

AAND & CYCLE LAMPS, TORCHES, ETC

A, H, HUNT, LTD., CROYDON, SURREY

Please Mention "A.W." When Corresponding with Advertisers

YOU CAN OWNTHE MULLARD

1S. G. P. DOWN

MASTER THREE FORThe latest in Radio Receiver design. First payment £1 and so monthly

payments of 14/-.Assembled by anyone. No trouble. Perfect results. Obtain all Europe. All -wires cut and looped. Baseboard with plan printed on it. COMPLETE KIT OFPARTS AS USED BY MULLARDS at the above payments or cash £7 4s.

Call and hear this Wonder Set.Write for our detailed list. Any parts sold separately'. Price of specified Kit withValves, £10 2s. Od. Cabinet for.this.set in oak, 25/-. Transportable Calenet,52/-. Long range Coils, MULLARD 10'6 pair. Combined Coils, long and short

range, 32/6 pair.-

10/- down secures a BROWNI-1.3 Genuine

LOUD -SPEAKERPay first instalment and three payments of 7,8.

CarriageOnly 400 left. Usual price £3 5s, od. Our PRICE

30/- cash or monthly payments.

CLARION THREEPay 15/- now and secure this marvellous Kit. Includingwire, baseboard and best quality ebonite panel and stripsready drilled. 15/- down and five monthly payments of 15/ -

or cash £4 4s. Od. (Valves extra),

Usually 3/510

NOW 30/-

BURNDEPT S.G. 4 -VALVE PORTABLE. Brings Europe's finest broad-cast programmes to your home. Beautifully made. Light weight. Our gradual

payments for this set: £2 down and s monthly payments of £2 Is. 4d.Limited number of Ediswan Dulcivox SPEAKERS. Makers' price,

£2. Our price, 1 9/6. Beautifully finished in original boxes.

GRADUALPAYMENTS

The very best terms possible on all wireless apparatus (SpeakersKits, Valves, H .T . Units, Wet Batteries, etc.) State your re-quirements and we will quote you by return. Immediate delivery.

Carriage paid on all cash orders.H. & B. RADIO CO.,34 BEAK ST., REGENT ST., LONDON, W.1 Ger. : 2834

720 MAY 18, 1929

"A.W." TESTS OF APPARATUSConducted by out Technical Editor, J. H. REY NER, B.Sc. (Hons.), A.M.I.E.E.

Graham-Farish CondenserTHE physical dimensions of differing

types of .0003 variable condensers donot alter appreciably; they are always ofa bulky nature and ample space must beprovided for when mounting them in a set.This question of condenser bulk is often a' problem to the designer, particularly inportable receivers, since it is apt to limit thepossibilities of a compact layout.

Graham-Farish variable condenser, witha bakelised paper dielectric

It was therefore with some interest thatwe Jested a new design Graham-Farish.0003 capacity variable condenser havinga bakelised paper dielectric. This condenseris housed in a cylindrical insulated casemeasuring ;A in. in 'diameter and Y8 in.thickness, .whilst the overall thickness,including the terminals, is approximately

in: It will therefore be seen that the spaceoccupied by this component is considerablylesrs than is usual for a variable condenser.This, taken in conjunction with the lowcost; is a desirable feature.

It must be remembered, of course, thatthe substitution of a paper dielectriC forthe normal air dielectric materially increasesthe H.F. resistance of the article and inconsequence the efficiency and selectivityof a set may be affected. Used in a normaldetector circuit with reaction,- the condenserresistance may be counteracted to a greatextent by increasing the reaction, althoughthis tends to make searching for distantstations a- more difficult procedure.

In other cases. particularly when utilisingscreen -grid circuits, the H.F. resistance ofthe tuning circuit must not be too low,otherwise chronic self -oscillation will occur.Thus it might be possible to wind efficientcoils and use these with the paper dielectriccondensers and so balance matters.

For a solid dielectric condenser,. themotion cs commendably smooth and hadthe feel of a normal air dielectric article

The capacity range was found to- extendfrom .0000r to .00037. At 40o metres theincrease of H.F. resistance in a circuit dueto the use of this condenser was of the orderof io ohms.

Junit Valve HolderTHE popularity of four- and five -elec-

trode valves has increased to a largeextent during the past year and it hastherefore been necessary to adapt them foruse with the normal valve holdei , althoughthis latter component is not always mostconvenient for these types of valve.

A valve holder made by the JunitManufacturing. Co., Ltd., of 2 RavenscourtSquare, W.6, Ls been designed speciallyfor use with the new four- and five -electrodevalves. It may be mounted either in ahorizontal or vertical position and willtherefore hold a screen -grid valve in thecorrect plane for screening.

An additional terminal is fitted to thehoider and serves as a junction for a flexiblelead to the extra terminal on the pentodeand a rigid connection to H.T. positive.

The four soCkets of the holder aremounted on a small square moulding and theconnections are taken out to four terminalsat the corners. Holes are drilled in the

Junit valve holder

moulding for mounting the holder in twoseparate planes. The component, which iswell -finished, should prove useful to setbuilders.

Loewe Loud -speaker UnitIOEWE components have from time to

time been reviewed in these columnsand generally show a degree of workmanshipand finish which is entirely commendable.The new loud -speaker unit is no exceptionto this rule, and is an exceedingly heat andserviceable component.

The simple electro-magnetic unit, whichconsists of a reed mounted in proximity toan electro-magnet, is housed in an attrac-tively finished moulded insulated former.An adjustment for the unit is controlled

by an external knob and comprises a pistonmovement attached to the reed via aspring. One of the Loewe vacuum variablecondensers is placed across the loud -speakerterminals in order to correct the tone.

We placed this instrument on test byclamping it in a floating cone assembly ofa known efficiency. Mounting was quitea simple matter since two lugs on themoulded casing are provided for this pur-

Loewe reed -type loud -speaker unit,incorporating a shunt condenser

pose. The results we obtained from ourtests, on reproduction of speech and musicwere good and compared favourably without standard cone speaker. There is nodrumming and speech is quite clear; at thesame time the reproduction is sufficientlymellow to give pleasing results on musicalitems. The extent of reproduction wasquite satisfactory for a unit of its type,being very nearly as good in this respect asour standard unit.

This is quite a high-class unit and can berecommended to readers.

HEAVISIDE-LAYER " WOBBLES "RECENT investigations have shown that

the surface limits of the Heavisidelayer fluctuate rapidly from minute tominute, particularly during the daylighthours. On one occasion the layer wasfound to rise at the rate of six miles perminute, and to fall at the rate of twentymiles per minute, over a period of approxi-mately a quarter of an hour. One possibleexplanation for this behaviour is the exis-tence of mysterious electric fields whichimpact on the outer atmosphere from inter-stellar space and swing the free electronsup and down in bulk. B. A. R.

The National Broadcasting Company inAmerica has contracted with 643 radioartistes to broadcast for it exclusively.

MAY 18, 1929 721 ematturWireit5

W RELESS IN PARLIAMENTiI

I ?JN

From Our Own Correspondent

VISCOUNT WOLMER informed ColonelWoodcock that the following revised

licences hadarrangements for wirelessrecently been introduced :-

(1) A wireless licence covers the use inthe premises occupied by the licensee ofany number of sets of receiving apparatusof any character by the householder, hisfamily and his domestic staff. (A separatelicence is necessary for a separate building,such as a lodge or gardener's house, or fora portion of the same address under aseparate tenancy.)

(2) A wireless licence covers the tem-porary use (for example, during holidays)of receiving apparatus of any character atanother residence, provided that no re-ceiving apparatus is being worked at thehome address.

(3) A wireless licence covers not only theuse of wireless sets at one fixed address,but also the use (whether simultaneouslyor not) of one portable set at any place inGreat Britain or Northern Ireland by thelicensee or any member of his household.When a portal.* set is used away from thehome address (for example, on a motor-car) the person using it must carry thelicence with him and produce it if askedto do so by an authorised officer of thePost Office.

The concession in regard to portablesets takes effect immediately, but norebate will be allowed in respect of aseparate licence already taken out for aportable set. The conditions printed onthe licence form will be amended in duecourse.

A French author and playwright broughta libel action against P.T.T. Paris, as on arecent evening, in the course of its newsbulletin, the announcer stated that thedramatist had committed suicide.

A further super -power transmitter is to beerected in Sweden; the Stockholm stationwill be replaced by Marconi plant capableof supplying 6o kilowatts to the aerial.

A new law has been passed by theBelgian Chamber of Deputies dealing withthe organisation of a National Broadcast-ing Institute to be controlled by an officialCouncil with the Minister of Posts andTelegraphs as president. The institute willtake over Radio Belgique and the proposedLouvain station.

With the selecting of a tentative siteat Grand Island, Nebraska, for the masterradio monitoring station, the Radio Divi-sion of the U.S. Commerce Departmentbelieves it has determined the radio centreof the United States. This is the result ofmany months surveys and observations.

esnatearWirek 722 MAY 18, 1929

Weekly Tips,Constructional

andTheoretical-

Earth Connections

IWONDER what proportion of complaintsof poor results are to be traced to a

hurriedly constructed earth > I find theearth connection is often neglected, a pieceof wire being wrapped around a convenientmetal pipe. Even when a water pipe ischosen and the earth wire is carefullywrapped over a clean portion, the earth maynot be a good one.

Sometimes it is, of course, possible toemploy a short earth wire and to connectit to a clip fastened to a water pipe whereit is about to enter the ground, but in manyinstances it is better to provide an earthplate. This may consist of a sheet of zincor copper, two or three feet square. Theearth wire should be soldered to it and theplate buried in the ground.

If the earth wire happens tobe short and the plate is of reason-able size, the earth will be mosteffective and it is surprising howsignal strength and selectivity willbe improved. A good earth is al-ways worth while and will repayany little trouble taken over itsconstruction.

Curing Transformer DefectsDo you know the two principal defects of

poorly constructed transforMers? The firstis an uneven frequency response. Thismeans that the lower, middle, and highernotes are not magnified uniformly, with theresult that distortion is produced.

This is obviously to be avoided whenpossible, or at all events to be 'minimised,and in this connection it will be found thatthe addition of a grid leak will often improvematters. The grid leak should have a fairlylow value of resistance and be connectedacross the terminals of the secondary wind-ing of the transformer.

A suitable grid -leak to try would be onehaving a resistance of half a megohm, butthe most marked improvement in thequality of the reproduction may be ob-tained when a grid leak of one quartermegohm is used. The volume may bereduced a little when the grid leak is con-nected but the effect will be to improve theperformance as a whole.

The second defect referred to is due tothe use of poor iron for the core and results

DEN0\As, AMES

in the creation of harmonics. In otherwords, the output from the transformer isvery different from the input.

This form of distortion is unfortunatelynot to be minimised by the employmentof grid leaks or other accessories-which isa point to be remembered by those con-sidering the purchase of a very cheaptransformer.

A Stabilising ResistanceHigh frequency amplifiers employing

ordinary three -electrode valves are usuallystabilised by suitably arranging the circuitsin order that the capacity of the valves maybe neutralised. For this purpose a neutral-ising or balancing condenser is generallyused:

Another method of stabilising is, however,often used in foreign receivers and takes

A grid resistance used for stabilising

the form of a resistance included in the gridcircuits of the high frequency valves. Thisresistance acts to prevent instability whenit has sufficiently high value, because it isin a circuit which includes the capacity ofthe, valve as indicated in the diagram.

For a given value of resistance, thestabilising effect would be increased byraising the grid - to - filament capacity,marked c in the diagram. A similar effectresults when the resistance is increased.It is, therefore, possible to find by experi-ment a value of resistance which will ensurestability for any type of valve and thevalue of the resistance actually foundsuitable will depend, amOngst other factorsupon the capacity.

Making ConnectionsAttempts to introduce cable connectors

to replace the existing terminals and singlewires have, up to the present, not met withvery much success.

For theWirelessAmateur

I myself have used in a published set, acable or battery cord fitted with t46 -e neces-sary plug or socket but few followed myexample. 'Whether this was due to therelatively high cost of a six- or seven -wirecable fitted' with connectors or to the ideathat the connectors themselves were notalways satisfactory I do not know, but onemust admit that some' contact pins arenot very reliable. They are not of a suffic-iently robust construction, neither are theydesigned to be fool -proof. But these defectswill in time be removed and then I expectthe advantages of joining mains units orbatteries to a set by this method will berecognised._

Mass -production WiringThose who construct and wire their own

receivers take pride in so arrang-ing the various wires that when

set is not on+vefficient but good to look at.

. It is all very well carefully toshape and put in each wire in aset when time is of no great im-portance, but manufacturers have

. to consider cost and it is thereforea necessary for them to so simplify

OH the wiring that relatively unskilledpersons may be employed with the min-imum chances of mistakes occurring.

The usual practice in quantity productionis to employ a cable composed of the neces-sary number of different coloured con-necting wires. These may be shaped in adummy set and where the wires run' to-gether they may be bunched and laced withstring. Operators build up sets of wires andothers drop them in assembled sets andCommence the wiring. The wiring isusually carried out by a number of opera-tors, each one being responsible for a smallnumber of connections. This scheme isthoroughly satisfactory ,and results in thewiring being completed in a very short timewith the minimum of faults.

On a recent occasion a Dutch programmebroadcast by the Huizen (Holland)' high -power short-wave transmitter (PHI) wasrelayed to WGY (Schenectady, New York)and re -broadcast through thirty-five U.S.A.stations.

,;:1-wskidashilingsmies".

M AY 78, 1929 723 onbalawlvird

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71 rLOUD SPEAKERS

TN view of the fact that a new range ofi Brown Loud Speaker's is now in courseof production and will, at an early date,be placed on the market, the followingBrown Instruments have been withdrawnfrom production and credit has beenallowed on supplies returned by ourcustomers

Type H.3. Disc Type.Type H.3.Q. Cabinet T;;pe.C.T.S. Unit and Accessory Set.

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7/6

ellwitarWIrde5

IN ,,AMATEURWIRELESS No. 360

were given construc-tional details forbuilding up the re-producing and relayunits of the Fulto-graph, from the kitof parts supplied byWireless Pictures(1928) Ltd.

When all the parts are assembled as wasdescribed in this article, there remains acertain amount of wiring to be donebefore the picture receiver can be operated.The flex wires attached to the six -socket

holder at one col-ner of the Metal panel aresupported by clips on the underside of the

The Circuit Diagram of the Fultograph Relay Panel

panel and pass up again through a bushedhole at the other end of-the panel and areconnected to the switch blade contacts andso on.

Connecting PointsThe following will serve as a guide to

show how the connections are placed. (a)Long blade of the top switch to socketNo. 2; (b) stylus arm (black cable) also toNo. x on socket; (c) short blade of the topswitch on the magnet bracket to No. 2 onthe socket; (d) screw on anchor plate of ballbearing pedestal to No. 3 on the socket;(e) inner clutch ring contact to socket No.

(f) one end of the electro-magnet coilalso to socket No. 4; (g) long blades of thetwo middle switches to be connected to-gether and to socket No. 5 and (h) the other

Under Side of Relay Panel

724

13uildinaYour Ow

MAY 18, 1929

Concluded fromNo. 360

end of the electro-magnet coil to No. 6 onthe socket. Finally the short blades of thetwo bottom switches on the magnet bracketshould be connected together and to theouter clutch ring contact. The black wire

connected to the stylusarm, which goes to No.

socket, passes througha hole of its own in themetal panel.

Relay ConnectionsOn the relay panel are

mounted the milliammetermagnetic relay with aoI micrcifarad condenserunderneath, transformer,switch, and socket baseswith a resistance bobbinattached to the socketbase designated c/24. Anaccompanying diagramshows how all these parts

wired up. Tinned wire, cut tolength, is used and should be covered withinsulating tubing. All joints should besoldered except at the milliammeter,switch and input terminals where theconnections are made by nuts.

The wander plugs on the ends of thecable attached to the relay unit carryindications showing to which batteriesthey should be connected.

Operating HintsThe correct method of

Fultograph has been fullydealt with in previous issuesof AmATEun WIRELESS, butthere are one of two pointswhich are of. particularimportance to home con-structors. The followingpoints should be given atten-tion. The platinum pointof the stylus should bebent so that it touches thepaper at an angle of about70 degrees. A piece of thefinest emery paper should bpfixed round the drum sothat by rotating it slowlythe end of the stylus canbe slightly ground 'until itpresents a smooth face tothe paper.

Adjustment should bemade so that there is about

are to be

operating theIv con/ ace #1,??.4dutch mg

movement shouldadjusting screw.

Relay AdjustmentsTo test the magnetic relay make all

normal connections from the batteries tothe picture receiver but do not connect up

1/32 inch gapbetween the arma-ture and the magnetpole pieces whenthe catch is restingin the notch. Allowthe catch to dropinto the notch onlyjust sufficiently toprevent the wheelfrom turning. Its

be arrested by the

This Photograph shows the connections toMagnet Bracket

the loud -speaker. Put the G.B. negativeterminal into the 15 -volt tapping and theG.B. positive terminal into , the i8 -volttapping;. Switch on the relay and 'thenmake a few experiments with the H.T. plug.Put the plugs first into, say, the 75 -volttapping and notice if a click is heard fromthe relay. The click must also be heard ifthe plug is withdrawn. 'When the righttapping is found try rapid successive con-tacts and these should work the relay everytime.

The Circuit Diagram of the Reproducer Unit

MAY 18, 1929 725

,sn.ess,a,sam amseWI.12(14DIOGR(INIS

TN the 2L0 vaudeville programme to bebroadcast on Whit -Monday will be

found the names of Heather Thatcher andLawrence Anderson. These artistes willshare the microphone with Leslie 5arony,Geoffrey Gibson, and Bert Copley.

Cupid and the Cutlets, by Percy Green -bank, co-author of San Toy, The CountryGirl, To -night's the Night, etc., .is a newburlesque operetta,: of which the first per-formance is to be given by 5GB (Daventry)on May '30,

On May 25 the Moursgorsky quartet ofRussian singers will broadcast for the firsttime in the course of a variety programme

.arranged for that day. Fred Duptez,Yvette Darnac, Billy Thotburn, DorrieDean, Florence "Bayfield, and Ha.toldKimberley are included in the bill.

Sir Henry Newbolt, the' composer ofDrake's Drum, will be responsible for the2L0 Empire Day programme down fortransmission on May 24. .

Polling Day (May 3o) is to be celebratedby 5GB by the production of Vote-ville, anoriginal revue specially written for the:,casion by Alfred Butler, with additional

numbers by Graham Squiers.A short play in one act entitled The

Turn of the Tramp, from the pen of Con-stance Smedley, will be produced at theCardiff studio on May 3o.

All stations of the northern region duringthe summer season will take programmesfrom famous holiday resorts. The seriesopens on May 25 with a concert fromBlackpool, to be followed on ensuing claysby entertainments from Southport' andBuxton. Concerts are also to be relayedfrom Scarborough, Harrogate, andLlandudno.

A studio performance of Massenet'swell-known opera Le Jongleur de NotreDame is to be broadcast from 5GB onMay 27, and from 2L0, 5XX, and otherstations on May 29. It is described as amiracle in three. acts:

Listeners interested in thrilling advert.;tures of the sea should listen to a talk onmystery ships to be given by CaptainC. E. Harris from the Cardiff station onJune 1. He, was navigating officer of thei,mallest "Q" boat in the service, a ketchchristened :The Record Reign in honour ofQueen Victoria.

The Radio Paris luncheon -hour trans-mission now consists entirely of a broad-cast of gramophone records,

The application list for membership ofthe National Orchestra formed by theB.B.C. in co-operation with Sir ThomasBeecham closed on Saturday, May r r.During the autumn it is propcised toinaugurate a trial season with a view tothe establishment of a permanent sym-phony orchestra of about ninety musicianswho will be engaged on a full-time non -deputising basis.

The Swansea relay station has adoptedthe national common wavelength of-e88.5 metres; the change, however, is soslight that...very little readjustment in thetuning of listeners' receivers will be foundnecessary.

If it were practically possible to usewavelengths of from one to ten metresfor broadcasting purposes there would be,no difficulty , in accommodating some25,000 stations within those limits withoutany risk of mutual interference.

In addition to several short-wave trans-mitters already operating in the BelgianCongo, nine of the existing long -wavestations in that territory are being re -equipped for short-wave working in bothC.W. morse and telephony.

The Koenigswusterhausen and Nauengroups of short-wave telegraphy stations(situated near Berlin) will, it is understood,be augmented shortly by a number of newtransmitters designed to work on wave-lengths between 7 and 5o metres, which arenow under construction.

Dancing, firework displays and throwingof rice cakes were part of the inauguralceremony of the new wireless stationrecently constructed at Nagoya Prefecture,Japan, at a cost of 4,800,000 yen,

Twenty aeroplane licences and permitsfor ground wireless stations have beengranted by the Federal Radio Commissionfor a new aeroplane service between NewYork and Los Angeles to commence onJuly I. Eleven radio stations are to beerected at points along the route to furnishpilots with weather reports and other vitalinformation.

The proposed station in America to beused for checking the wavelengths ofbroadcasting stations will be erected atNebraska.

The Prince of Kambaelig Bejra, ministerof communications for Siam, has issued astatement that all radio apparatus in thancountry is banned at present.

(More Radiograms on page 727)

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YOU NEVER NEED BUY ANOTHER DRY H.T. BATTERYInstall the wonderful Standard Permanent Batteryand it will give you abundant H.T. that will LASTFOR YEARS. Hundreds of thousands of delightedlisteners use it. It recharges itself overnight, and inthe morning is full powered -as fresh as the dawn.Supplies a smooth non -sagging constant pressure ofcurrent that puts new tone in reception. Solve YOURR.T. problem once and for all. Install Standard.

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Running on an average of 3o hours per weekon an output of from 10-15 MIA, has given everysatisfaction, not been attended to in any way.

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This 16e -pp. Look furnishes the most complete i nformation ever publishedabout the many professional qualifications open to engineers such asA.M.Inst.C.E., Mech.E., A.M.LE.E., die.; describes over 150Courses; tells how employers every week fill vacancies with T.I.0.13.students and is crammed with matters of interest to every engineer.It you are ambitious, The T.I.G.B. can help you. Write TO -NIGHT foryour FREE copy of " The Engineer's Guide to Success " to

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OUR BLUEPRINT SERVICEConstructors of receivers described in this burns!should make full use of our Blueprint Service an.i

avoid all risk of failure.

It111) ROAD CAST TELEPHONY

(Broadcasting stations classified by country and in order of wavelengths)Kilo- Station and Power

Metres cycles Call Sign (Kw.)

GREAT BRITAIN25.53 11,751 Chelmsford

(5SW) 15.0243.9 1,230 ...Newcastle (SNO) 1.0258.6 1,260.1 'Leeds (2LS) ..0.13288.5 1,040 *Sheffield (61..F.)0.13288.5 1,040 *Bournemouth

(6BM) 1.0288.5 1,040 *Edinburgh

(2EH) 0.35288.5 1,04o *Hull (6KH) 0.2288.5 1,040 *Dundee (2DE) 0.13.288.5 x,o4o *Liverpool (6LV) 0.13288.5 x,040 *Stoke-on-Trent

(6ST) 0.13294.1 1,020 *Bradford (21.S) 0.13294.1 1,020 *Swansea (5SX) 0.13302.6 99/.1. Belfast (25E) 1.0311 964 Aberdeen (2BD) 1.0323 928 Cardiff (5WA) 1.0358 838 London (2L0) 2.0378 793 Manchester

(2ZY) 1.0396 757 *Plymouth(5PY) 0.13401 748.3 Glasgow (5SC) 1.0482 . 622 Daventry Ex.

(5GB) 17.01,506.5 191.5 tDaventnr

(5XX) 25.0* Relay stations. tRelays 2L0.

AUSTRIA250 1,200 Linz 0.5277.8 1,080 Salzburg (under

construction) 0.5283 r,060 Innsbruck 0.5354.2 847 Graz 0.5'456 694 Klagenfurt 0.5520 577 Vienna 20.0

BELGIUM220 1,360 Chatelinean 0.25249 7,203 Schaerbeek-

Brussels 0.5275 1,090 Ghent 0.5280 1,070 Liege 0.5312 96o Arlon 0.25512 06 Brussels 10.0

CZECHO-SLOVAKIA265 1,228 Kosice 2.0278 x ,o8o Feriby (testing) 12.0305 982 Bratislava 4.0343 873 Prague (Praha) 5.0432.3 694 Brunn (Brno) 2.4

- 339 883 Copenhagen(Kjobenhavn) 1.0

1,156 259 Kalundborg 7.5

ESTHONIA408 735 Reval (Tallinn) 1.3

FINLAND374 Soo lielsingfors

(Helsinki) 0.81,502 /99 Lahti 20.0

FRANCE175 1,714 St. Quentin 0.25200 1,500 Decamp 0.3211.8 1,420 Beziers 0.1238 z;z6o Bordeaux (Radio

Sud-Ouest) 2.0240 1,250 Radio Nimes 1.0245 2,22 4 Line (PTT) 0.8252.1 1,190 Juan-les-Pins 0.4254 z ,r8o Rennes (PTT) 1.0255 z,z75 Toulouse (PTT) 1.0268 1,1 r8 Strasbourg 0.3

Kilo- Station and PowerMetres cycles Call Sign (Kw.)

274 2,092 Limoges (PTT) 0.5285 1,050 Montpellier ... 1.5292 1,028 Radio Lyons ... 1.5300 996 Bordeaux (PTT) 0.5304 982 Marseilles (PTT) 0.5305 982 Agen 0.3322 930 Vitus (Paris) 2.0336 892 Petit Parisien 0.5353 849 Algiers (PTT) 2.0368 815 Radio LL, Paris 1.0382.2 785 Toulouse (Radio) 9.0400 749 Mont de Marsan 0.4413 725 Radio Maroc

(Rabat) 2.0423.7 798 Radio Flandre

Lille 0.25429 699 Grenoble (PTT) 1.5450 666 Paris (Ecole

Sup., PTT) 0.7468.8 640 Lyons (PTT) 5.0

1,478 203 Eiffel Tower 8.01,749 17r Radio Paris , 8.01,825 164 Radio Carthage

(Tunis)

GERMANY219 1,370 Flensburg 1.5240 1,250 Nurnberg 4.0250 1,200 Kiel 0.7260 1,200 Cassel 0.7263.2 1,140 Cologne 4.0267.8 1,720 Muenster 1.5273 z,099 Kaiserslautern 1.5280.4 1,070 Kdnigsberg 4.0283.1 .7,058 Berlin (E) 0.7283.1 x,o58 Stettin 0.7283.1 1,058 Magdeburg 0.731.7.5 945 Dresden 0.75320 937 Breslau 4.0326.4 gig Gleiwitz 6.0329 9ro Bremen 0.75361.9 829 Leipzig 4.0374.1 8o2 Stuttgart 4.0391.6 766 Hamburg 4.0427 7zr Frankfurt 4.0455.9 654 Danzig 0.75456 65r Aachen 0.75462.2 649 Langenberg 25.0476 630 Berlin 4.0638 558 Munich 4.0566 530 Augsburg 0.5666 530 Hanover 0.7577 520 Freiburg 0.7

1,653 181.4 Zeesen 20.01,648.3 /82 Norddeich 10.0

GRAND DUCHY OFLUXEMBOURG

1,275 235 Radio Luxem-bourg 0.25

HOLLAND31.4 9,554 Eindhoven

(PC J) 25.0.38.8 - Kootwijk

(PCL) 32.0(Wed. 1.40 p.m. B.S.T.)

336.3 891.5 Huizen (until6.40 p.m. B.S.T.) 5.0

1,076(ANRO) 5.0

1,846 x62.5 Huizen (after6.40 p.m. and on

Sundays 5.01,846 2-62.5 Scheveningen -

haven 5.0

HUNGARY548 548 Budapest '15.0

ICELAND333.3 goo Reykjavik 1.0

Kilo- Station and PowerMetres cycles Call Sign (Kw.)

IRISH FREE STATE222.2 1,350 Cork (5CK) 1.5411 730 Dublin (2RN) 1.5

ITALY276 z,o8o Turin 7.0333 goo Naples (Napoli) 1.5387 775 Genoa (IGE) 3.0_442 677 Rome (Roma) 3.0450 666 Bolzano 0.3603.5 596 Milan 7.0

JUGO-SLAVIA308.3 973 Zagreb (Agram) 1.25458 655 Belgrade 4.0682 5x5 Ljubljana 5.0

LATVIA529 567 Riga 2.0

LITHUANIA2,000 15o Kovno 15.0

NORWAY242 1,240 Rjukan 1.0297 x.ozo Notodden 0.7365 82o Bergen 1.0387 774 Fredriksstad 1.0456 657 Tromso 1.0456 657 Aalesund 1.0456 657 Porsgrund 1.0406 604 Oslo 1.5577 50.9 Hamar 0.7

POLAND314 955 Cracow 1.6337 890 Posen 1.6415.5 722 Kattowitz 10.0456 658 Wilno 1.5

1,397 214 Warsaw 10.0PORTUGAL

317.5 945 Lisbon CTI A A (Wedand Sat.: 10 -midnight)

ROUMANIA395 757 Bucharest 4.0

RUSSIA492 609 Kharkov (NKO) 5.0825 363.6 Moscow (PTT) 25.0925 323 Homel 2.5

1,004 299 Leningrad 20.01,450 206.9 Moscow 30.01,698 178 Kharkov 15.0

SPAIN314 956 Oviedo (EAJ19) 0.5346.8 865 Barcelona (EAJ1)10.5369 821 Seville (EAJ5) 0.5400 750 Radio Espafta 1.0405 74o San Sebastian

(EA.'S)428 700 Madrid (EAJ7) 3.0456 658 Salamanca

(EAJ22) 0.55SWEDEN

261 .r,r so Horby 10.0265 1,130 Trollhattan 0.4333 goo Falun 0.5350 80 Goteborg 6.0437 686 Stockholm 1.5

550 546 Sundsvall 1.0770 390 Ostersund- 2.0

1,200 25o Boden 2.01,350 222 Motala 30.0

SWITZERLAND406 739 Berne ...... 1.0496 604 Zurich 0.6680 44r Lausanne 0.6760 395 Geneva 0.5

1,010 297 Basle 0.25TURKEY

1,200 250 Stamboul 6.01,809 /64 Angora 5.0

CHIEF EVENTSOF THE WEEK

LONDON AND DAVENTRY (5XX)

May 19. British Legion Service from the Cenotaph.23. People's Palace Concert.24. Empire Day Programme.

DAVENTRY EXPERIMENTAL (5GB)

May 22. "Cabaradio," by Charles Brewer.23. Two Plays -"The Pierrot of the Minute," a

dramatic fantasy by Ernest Dowson, and "TheMan with 'the Flower in his Mouth,''. adialogue by Luigi Pirandello.

Covent Garden Opera.1. 24.

CARDIFF

May 22. A Variety Programme.

May 20.

May 22.

May 2o.

MANCHESTERRunning Commentary on Lancashire v. York-shire County Cricket Championship, by Mr.A. E. Lawton.

GLASGOWA Mixed Menu served by the Radioptimists.

ABERDEENA Scottish Concert.

Interviewed at the Ritz Hotel, London,recently, Mr. Merlin. Aylesworth, presidentof the National Broadcasting Company inAmerica, stated that, as a result of a seriesof conferences with British broadcastinginterests, arrangements have been com-pleted for a regular exchange of broadcastprogrammes between England and Americato start in a very short time.

278 Hilversum

MAY 18, 1929

MORE RADIOGRAMSTHE province of Victoria, Australia,

has more than eight wireless sets forevery too persons,

About' 90 per cent. of all the radio equip-ment in the world is of English, American,and German origin, according to figurescompiled by the United States Departmentof Commerce.

More than 95 per cent. of the sets now inme in America are valve receivers.

Whatever, the song request addressed toWNER, Chicago, there is a good chance ofit being found in the musical library of thatstation. In this library there are more than78,000 sheets of music.

The Czechoslovakian telegraph authori-ties have recently placed a contract for theestablishment and equipment of a short-wave wireless telegraphy station at Pode-prady, near Prague.

The directors of the Greek Postal andTelegraph Administration have completedthe programme for the extension of thepostal network for wireless telegraphy.For coastal services, particularly withships, four wireless stations will be estab-lished at Attika, Sitia, Salonica and on theisland of Zante. The internal radio networkis to be extended by the establishment ofthree stations.

A large radio exposition will be held inthe Kursaal at Scheveningen from May 17to 25.

According to the Washington Conferencethe following wavelengths have beenallotted to television and still picture trans-missions : 64,000 to 56,000 khz., i.e., 4.69to 5.35 metres; 2,000 to 1,75o khz., i.e.,15o to 175 metres.

To coincide with the official opening ofthe Barcelona International 1929 Exhibi-tion this month, the EAJI broadcastingstation has been increased in power to tokilowatts. Tests are now being carried outin the late evening hours on a wavelengthof_35o.5 metres. An interesting programmeof relays to the transmitter has beenarranged during the period of the Exhibitionand foreign listeners will hear broadcastsmade from the.Greek Theatre, the Stadiumand the specially constructed Spanishvillage enclosing_ 'an arena 'in which galabull -fights are to take place. RadioCatalana, (EAJ 13) which has .also beenreconstructed will also transmit on higherpower.

The French military authorities haveequipped an army motor lorry with short-wave wireless transmitting and receivingapparatus for experiments to be carriedout in the Sahara Desert. A small radiostation is to be installed at Timbuctoo, thebase headquarters of the expedition.

On May 15, Holland introduced summertime by advancing her clocks by sixtyminutes; this alteration will bring her timeforward by 20 minutes in advance of B.S.T.

727

Some interesting outside broadcasts areto be carried out by the Paris P.T.T.station, Ecole Superieure and its provincialrelays in the near future, one of which, onMay 19-20, will consist of a running com-mentary on the aviation fete to be givenat the Polygone de Vincennes by Jean derHorter, the famous parleur inconnu, whowas responsible for the eye -witness accountof the international football match (Francev. England) which took place at Colombes,near Paris, on May 9.

A further meeting of the U.I.R. (UnionInternationale de Radiophonie) will takeplace at Lausanne (Switzerland) on May27-31. Another wave plan ?

On the occasion of the total solar eclipse,which took place on May 9, birt of whichobservations could only be made in Siam,the Dutch East Indies, Cochin China, andthe Philippine Islands, a commission ofFrench physicists and astronomers at PouloCondor carried out elaborate preparationsin order to note the influence of the eclipseon short-wave transmissions. For thispurpose, amongst others, a small trans-mitter was installed on a sailing boat, andat regular intervals a series of short dasheswere broadcast on wavelengths of 3o and40 metres. PCJ (Eindhoven) was alsobrought into action and put out at periodsof 15 minutes a calibration signal, frequent-ly interrupted by the station's call.

At Saarbrucken (Saar), on the site of theold Petersberg telegraphy transmitter, theFrench authorities have decided to erecta broadcasting station. Although it ismainly to be used for aeronautical services,it is expected that during a portion of theday and evening it may be devoted to aprogramme of wireless entertainments, asfor the present the inhabitants can onlyreceive the German broadcasts.

In view of mutual interference caused tostations working on the common wave-length of 455,9 metres, the Rayag (Vienna)authorities ordered Innsbruck to operateon 283 metres. As, however, no improve-ment to the broadcast has been noted, itis expected that this relay station will seekanother position in the waveband.

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That is why it is possible to offer thishigh-grade dial at the wonderfulprice of 3/6.The mechanism is a special non -backlash design with a reductionratio which makes fine tuning easywithout becoming tedious.Obtainable from all wireless dealersin beautifully finished plain black orlovely grained mahogany bakelite.

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728

WINDING YOUR GRAMO.PHONE ELECTRICALLY

ITis now possible to wind your gramo-

phone electrically, and automatically,without any attention whatever. Thedevice by means of which this can beaccomplished is the A.E.D. self-windingmotor, which combines the convenience ofelectric drive with the dependable accuracyof the spring motor.

Briefly, it consists of an electric motorconnected to a spring motor of the ordinarystandard type through the intermediary ofreduction gear. The arrangement is shownin the photograph. The gearbox is con-nected to the winding shaft of the springmotor by means of a coupling consistingof one member fixed to the winding shaftand one sliding member which is held inengagement by an adjustable coil spring.

When the spring motor is wound to suchpre -determined point that the tension ofthe main spring exceeds the tension of the

The A.E.D. self-windingGramophone Motor

spring which keeps the coupling in engage-ment, the loose member of the coupling isforced back out of engagement with thefixed member, thus freeing the windingshaft of the spring motor from the electricmotor. Upon the disconnection between theelectric motor and the spring motor takingplace, the electrical circuit is broken.

If it is desired to use the gramophonewithout making use of electric current, itcan be wound up by hand in exactly thesame way as any ordinary spring drive.The winding motor is universal and can beused on both A.C. and D.C. circuits (allvoltages).

It will be understood that for use withelectrically amplified gramophones, thismotor is of particular interest, as all riskof interference from the electric motor iseliminated. The current consumption isexceedingly low as the electric motor isonly actually in 'service for about 3oseconds at intervals of 3 Y2 minutes.

Since January r, 1929, Germany hasincreased the number of her licensed broad-cast listeners by 202,327, thus attainingon April 1, the grand total of 2,887,894.

Change of Address.-Messrs. ClimaxRadio Electric Ltd. notify us that owingto ,increase cE business they have removedto Haverstock Works, Parkhill Road,Hampstead, London, N.W.3.

MAY 18, 1929

THE NEW GRAWORConstructor's

CONE UNITas specified and used in

The "TALISMAN" Portabledescribed in this and last week's issues.

This new " Grawor " Constructor's Cone Unitis an outstanding example of the enormousefficiency which has resulted from the long andcareful research upon which the name of"Grawor " has been built up.

This new Unit is intendedfor the Home Constructorfor use with permanent orPortable Loudspeakers. Itis solidly constructed yetweighs only 8 oz.

The Reed is ofample length andis suitable for anytype of diaphragmincluding of coursethe latest designsof linen diaphragmLoudspeakers.All metal parts areeither heavily nick-elled or speciallybronzed to preventrust due to damp-ness.The tonal qualityis exceptionally

Cone and Felt 116 extra. good and greatvolume

is obtainedAll as specified. for the without the slight -

Talisman' Portable. est distortion.Build your next Loudspeaker with this new"Grawor "Constrictor's Cone Unit and you will

never regret your choice.Obtainable from all Dealers, or direct from

larAW

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Sole Agent and Licensee for Great Britain.

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CABINET £2 5 .SAFETY FUSE I 6SCREENS ASSPECIFIED 4 6

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and insured, charges forward.

READY RADIO SUPPLY CO.159, Borough High Street,

London Bridge, S.E.ITelephone : Hop. 5555

MAY 18, 1929 729 ntuteur Wirele.5

Improving Reproduction.Q.-I have an L.F. transformer which is about

a year old, and find that even though this is usedin the second stage of L.F. coupling, with R.C.coupling in the first stage, there seems to be a con-siderable improvement in the quality of reproduc-tion by putting a small capacity fixed condenseracross the primary winding. Is this as it shouldbe, and is the use of this condenser likely to giverise to any detrimental effects in the receiver ?-S. A. (,Bath).

A. --The use of the condenser in questionwill not in any way be detrimental to thereceiver. Even with transformers not designedto have a fixed condenser in their constructionit is often an advantage to fit one, as such acondenser often alters the band of frequenciesto which the transformer will respond to thebenefit of the amplifier and loud -speaker ingeneral. As you have found this condenser tobe an improvement, we would advise you toretain it in circuit. -L. C.Grid -leak Connections.

Q.-In some circuits the grid leak is joinedacross the grid condenser, while in others it isbetween the grid of the detector valve and one sideof the filament. What determines which way thegrid leak should be connected?-R. A, C.(Brighton).

42011111111111,71/1/41,7 ,tooloree,

'/// ///1111111111111110

PULES.-Please write distinctly and keep to the point. We reply promptly by post. Please give an necessary details. Ask onet,uestion at a time to ensure a prompt reply, and please put sketches, layouts, diagrams, etc., on separate sheets containing your name;Ind address. See announcement below. Address Queries-AmArEurt WIRELESS Information Bureau, 58/6r Fetter Lane, London, E.C.4

'A.-In Of an H.R. transformer, placing the grid leakacross the condenser virtually connects itbetween grid, and filament. When, however,

0 0 0 0-0 0 the detector valve follows a stage of tuned -anode coupling, the grid leak must not be con. -fleeted across the grid condenser as this would

° result in it being connected, through the tuned -0 anode,coil, between the detector grid and H.T.

positive -.---R. E.

Cram Radio.Q.-I am using a pick-up with my receiver,

the amplifier portion of which consists of oneR.C. stage and one push-pull stage. Ordinarilymy wireless reception' on a moving -coil ldud-speaker is all that one could desire, but as soonas I put on the pick-up, especially with sOmYrecords, reproduction seems distorted. The pick-up is of good make. Can you suggest anything ?-I. F. (Dublin).

A.-You are overloading the valves in youramplifier. The pick-up may be rather tooefficient for your particular amplifier and thefirst valve is being badly overloaded. Wesuggest that you fit a volume -control acrossyour pick-up and in this way regulate theamount of energy applied to the grid of thefirst amplifying valve. The use of a controllingdevice will be quite satisfactory.- X. 0.

both casesbetween the grid and

of PLEASE write briefly- and to the point

A Fee of One Shilling (postal order">. or postage stamps) must accompanyo each question and also a stamped

addressed envelope and the couponwhich will be found on the last page.Rough sketches and circuit diagramscan be provided for the usual query fee.Any drawings submitted should be senton a separate sheet of paper. Wiringplans and layouts cannot be supplied.

the grid leak is reallyfilament. When the side

V\°/ *\I \ '1°1 VVVVag

0>0>

When AskingTechnical Queries

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ro

of the grid condenser farther from the grid ofthe valve is connected to the filament circuitthrough either a tuning coil or the secondary

maitat WtretT 730 MAY 18, 1929

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111

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NEW IMMO SALES CO.,56 LUDGATE HILL, LONDON, E.C.4

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ELECTRADIXBARGAINS

GREAT

Accumulator SaleSend addressed envelope for List.

THERMO BLINKS. Automaticallyopen and close circuit through re-sistance. Fitted adaptor and lampholder. Work a 60 watt lamp assign flasher well. 2/6 only, listed 7/6.Final Edition of our Surplus List of Radio and ElectricalGoods ready. Send stamped addressed envelope. Saves

radio users pounds.

ELECTRADIX RADIOS,218. Upper Thames Street, E.C.4131ackfriars Stn. Underground Rly. City 0191

BUILD YOUR OWN

BROWNS' LOUD SPEAKERCOMPLETE Construction Kit C.T.S. 10/6 List 16/ -

DROWNS' H.3 Loud Speakers 27/6 £3 0 0

H. 3 Q. 3C/- £3 5 0

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Cabinet Model 0/1 £6 6 0 2

EDISWAN Dulcivox Loud Speakers 1C/3 £1 11 6

Special Lines cannot be repeated at the price.TRADE TERMS on application. Letters only.

HUGOS,51, NAPIER ROAD, LONDON, NIL

IET 'Y'Amateurour .rWelireleess pss-bSlolve

LETTERS TOTHE EDITOR

The Editor does not necessarily agree withthe views expressed by correspondents.

The " Clarion Three "SIR,-Having built the "Clarion Three"

as described in AMATEUR WIRELESS,I feel that I must write and offer mythanks for publishing the details. I amvery pleased with the results.

To mention a few stations I have re-ceived at full loud -speaker strength, thereare Radio Paris, Cologne, Budapest, Hil-versum, Frankfurt, Brussels, and otherstations I have not been able to identify.London and the two Daventrys come in atterrific volume.

The valves I am using in the set are aMullard combination, being a PMI2,PM2DX, PM2, with 120 volts on the platesof all three, with 78 volts on the screenedgrid, and this works very well.

P. (London).

Condenser DefectsSIR,-I have a grouse about the majority

of tuning condensers-the round sec-tion of the main spindle. Most of -themoderate -priced S.M. dials can only befixed by a small set screw, with a smoothbevel point, which, in the case of the lock -vane type of condenser does not standmuch usage. There is an almost unavoid-able " jar " when the condenser stops ateither end, and in time this causes thepoint of the screw to wear a groove in thespindle and makes accurate "logging"impossible, as once the groove is there thedial "slops" about. Even filing a flatdoes not cure the trouble for long.

Why the makers do not fit a squaresection spindle is a mystery to me; itsaction would then be absolutely reliable,even should the screw loosen. On an oldArmy Mark III condenser I have, thespindle is square section, with knob anddial fixed by a screw running lengthwiseinto the end of it, and nothing could bemore immovably correct.

No doubt professional assemblers wouldscoff at my complaints, but amateurs haveto use the components as supplied, and theround -section spindle is thoroughly bad,unless a threaded hole is used for the grubscrew, which is not possible in this case, asthe dial has to be adjusted after the con-denser is fixed.-B. F. (Rayleigh).

Moving -coil v. Linen -diaphragmSIR, Your correspondent F S. (Lon-

don, S.) is, no doubt, quite right whenhe says the linen -diaphragm -loud -speakeris not equal to the M.C. operated underideal conditions; but he does not say whatis the ideal condition. There are not manyfortunate enough to possess the conditionslie, no doubt, has in mind. Now, as ithappens, I have, and have operated

M.C.'s and have listened to them at theexhibitions, and yet I would not run oneas a regular thing at any price. The resultproduced does not, to my mind, suitordinary household needs.

The M.C. has -its drawbacks, the sameas any other reproducer, this being accord-ing to the taste of the listener. One fault isthat the higher frequencies are smotheredby the lower, and this condemns it frommy point of view. I don't say that the"linen" is faultless, 'its fault being that itdoes not produce the higher so well as thelower notes, but it does not smother. .

Personally, I use a combination of a" linen" speaker in conjunction with afirst-class horn speaker, the last namedbeing modulated just to bring out thedeficiencies of the former, and I must saythat I am convinced that even F.S. wouldagree that the result is all that one coulddesire. I may say here that I have as finea set to produce results as one could wishfor.

My "linen" speaker is not the square -frame type, but has circular cones, whichI think are a great deal easier to makeand far more substantial.-A. G. (Bolton),

Undistorted RectificationSIR, Regarding "Thermion's" remarks

that it is an exceedingly difficult featto obtain anything like perfect and undis-torted rectification of strong signalh, Iwould draw your attention to the charac-teristic curve of the P.M. DX valves orMarconi DEL class. Valves of this typemake very efficient anode -bend detectorsif used to handle large inputs; if, however,the input is small distortion will result:I trust you will see the meaning of myremarks.

The greater part of the curve of thesevalves is straight, with a well-defined bendat the bottom, if weak signals are appliedthe valve will be working on or near thecurved part of the characteristic, also theimpedance under these. conditions will becomparatively high, making it necessaryto use a high value of anode resistance forthe following stage, with the resultant lossof the higher frequencies.

However, if the input is large, aboutto volts swing fully to load the detector,there will be very little distortion, for thesignal will be applied to a much greaterpart of the straight portion of the curveand the outpUt for all ordinary purpose:will correspond to the input. Again, thiimpedance of the detector working undethese conditions will not be much monthan about twice the maker's rating; thua coupling resistance of some 50,000 ohmmay be used with the resultant amplification of the higher frequencies.

It is quite difficult to overload a detectoof this type, for what single screen -gritvalve can deliver an output to overloadvalve capable of handling to volts griswing at any reasonable distance?

E. A. S (Chigwell).(Continued on page 732)

MAY 18,1929 731 (Imam Wirelesi

MAKE THIS WONDERFUL RECEIVER

The CLARION SCREENED GRID 3DEFINITELY CUTS OUT 2L0 AT 1tinent al Stations with 2L0 working.designer of set.

MILE and obtains 5GB, 5XX and. Con.This actual test has been made by the

KIT OF PARTS"A.W." 9=3-29

Any erne, Condenser, H.F Choke,or L.F. Transformer, supplied by

adding balance.2 Polar .0005, No. 3. at 5/9. .0001Reaction 4/.., 2 Dual range C.T.Coils, with Reaction (Tnnewell),Anode 10/6; Aerial, 10/6, 3 Lotus orW.B. V.H. at 1/3. Formodenser,J,- 2/-. Dubilier 2/9. .01Fixed, T.C.C., 1/9. 3-meg. Lissen orEdison Bell, 1/-. S.G. H.P. Choke,Pete - Scott, V-. H.F. Choke,Lissen, 5/6. L.F. Transformer, 11.1and Varley, 15/-. Ebonite Strips.14x7 Ebonite Pare, Sateen,8 Engraved Terminals. Push-pullSwitch, Flex, Plugs, 10-g. Wire,S.M. Dials.

THELOT

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.0002 Fixed and Series Clips 1/6 extra.1/6 EXTRA C.O.D.

American Type CABINET,Polished Oak Colour, Baseboard11x7x9, 12/6. Extra quality, 16/6.VALVESScreened Grid, Marconi, Mullard,Six -Sixty, 22'6 each. Detector, 10/6.

Power, 12,6.

CLEARTRONS.C., 12/6. C.T.15, L.F. or H.F.,9/, C.T.15, Power, 6/,

Brown L.F. Transformer,30/, Reed type Head-phones, 4,000 ohm, 20/-.Horn type £6 6s. Speakernow 63/, Electrical Pick-up, with adaptor plug,28/..Exide L.T. Batteries. Stan-dard CZ4, 40 amp actual,2 volt, 13/6; in crate, 19/-.4 volt (2 cells), '33/3 (incrate). 6 volt, in crate, 3cells, 47/9. Can only besent by train if ampleamount for carriage andparking sent. Surplus re-turned.9Peciai Indoor Aerials, phos-phor bronze wire, eboniteseparators, 12 ft. x 8, makingtotal 100 ft., 4/11, Post 3d.Lotus V.H., 1/3. Var. Con-densers, 5/-, 5/3, 5/6, 5/9Remote Control, 30/-; extraroom, 7/6. Master 3 StarDual, 15/-. Jack Switchesfront 2/, Vernier Dials,Brown or Black, 4/9. Post6d. ea eh.

S.L.F. Variable Condensers,ebonite ends, .0005, .0003,a really wonderful offer,complete with 4 -in. Dial,3/11. Post 6d. each,Lissen Electrical Pick -Up,the finest at the price. With-out adaptor, 15/-. Withadaptor, 16/6.Peto-Scott, .00(11 Reaction,4/6. Screened Grid H.F.Choke, 5/-. Post 3d, each.

Philips' Type 3002. High -Tension Supply Unit forA.C. Mains, 47. Type 3003.High -Tension Supply Unit,with Grid Bias, for A.C.Maine, £8 15$. Type 3005.High -Tension Supply Unitfor D.C. Mains, £3 17s. 6d.

Type 450. Low -Tension Bat-tery Charger for A.C. Mains,£3 10s.Philips' 2 -Valve All -electricReceiver for A.C. Mains.Price complete, £12 10s.

Philips' Loud -speaker (Type2026 or 2016), price £2 10$.

Brownie Crystal Set (200-1,700 nintres), Latest ModelNo. 3, 12/6. krair 4,000 -ohmHeadphones, 7/6. Aerialand Lead-in, 2/11. The abovelot. 18;11. Post 1/3Short-wave Coils D.X., setof four, 7.6.Climax H.T. Unit, 100 to 240volt, 10 tappings, 34/-,Potential Divider, 10,000 or20,000 ohms, 5/. eachSpecial Choke, 10/6. L.F.Choke, 8/6. H.F. Choke,7/6. KIt of 2 matched forMallard 5, 15/-, Post 6d.under 10/ -Ferranti Anode Resistances,3,000 ohms, 5/-; 20,000, 4/-;40,000, 4/- each. Completewith Holder, 2 Mid. Mans -bridge, 3/6. AF3 L.F. Trans-former, 25/-. AFL 17/6.Post 3d. each.

R.I. Mass Suspension GramoPick-up, 63/-. Gramo AutoPick-up Arm, 35/, BtDuplex W.W. R.C.C. Coup-ler, 20/-; "C," 17/6; "D,"16/-. Straight-line L.F.,25/-. Anti-mobo, W.W.Resistances, with holder,from 5/6.Magnum Centre -tapped L.F.Choke, 20/40 henries, 15/-.Wavetrap, 15/-. Titan (ap-proved) Coil Unit, 15/-.Standard Screens, AutoFuses, etc., stocked. Poet ex.Watmel H.F. Choke, 5/-.Post 6d. Dual Tuner, 12/6.

Igranis " F " type L.F.Choke, 15/-. "J" Type L.F.Transformer, 17/6. 3-1, for10/20,000 impedance; 6-1 5to 10,000. Lokvane variablefrom 8/6. Standard 8-1Dial, 6/-. The new 500 to 1ratio, 9/8. Post 6d, under10/,/Ohm Moving -soil Milliam-meters from 25/, MovingIron from 10/- P.M.Sifam New Model PocketVoltmeter, H.R., 4,000 ohms,heavy nickel case, 7/6.T.C.C. Fixed Condensers,.001, .002, 2/4 each. .0001 to0005,1/10; .01, 1/9; .1, 1/10.

1 mkt., 2/10; 2 mfd., 3/10.Post 3d. each.Double Reading (0-6, 0-120)Voltmeters, for H.T. andL.T. A very special offer.5/3. Post 6d.

Formo Valve Holder, 1/3.1028 Log, .0005, .00035,.00023, each 5/, De Luxe,.0005, .00035, .00025, .00015,6/- each. S.U. Coils, 1 and 2,10/6 each. Formodenser2/- each. Output Trans-former Filter Choke, 25/-.Post Od, each extra under10/-.

Dubilier Midget Condensers,qqp005, .0001, or .0002. 5/6

e1Tch. R.C. Coupling Unit,7/- (with VII., 8/6).

Cone Chassis. Blue Spot(Hughes' Ideal), 12/6 Good-man, 12/6. Squire, 15/6.Geared 2 -way Ebonite CoilStand, long handle' with 4terminals, B.B. Wonderfulvalue, 3/11.

J.B. Variable Condensers,.0003, 10/6; .0005, 11/6, with4 -in. dial. New type, 40-1,S.M., .0005, 14/6; .00035,13/6; .00025, 13/-; .00015,13/-. See elsewhere for thenew Drum Control, J.B,31.3 S.G.

Utility "Mite" Vernier Con-densers, .0005, for portables,10/-. .New Type Switches,2 pole, V.; 3 pole, 6/-, etc.Post 3d. each.

Dubilier K.C. Geared Con-densers, Max. .0005, 12, -.With Drum Dial, 15/.

Cossor New Model L.F.Transformer, 21/-.

Oak American Type, Hinged Lid,BEST QUALITY. Panel and Dial NOT included.

14x7, 14/11 16x7,16/11 18x7, 18111 21x7, 21/.Post 1/6, C.O.D. Extra. Advt. May 11, error in prices.

DARIO R A D IMICR°O2-v. or 4-v. G.P. 5/6Super Power .. 7/6Super H.F., 2-v. or 4-v. 7/6

Post 3d. (3 Post Free).

ORMONDS.M. Drum Dia1,5/.; Rheostats,O,15,30 ohm, 2/-; Midget.0001 max.,0/-; Log .0005 and 410. 6/-;Log. meg and 4,,n. Dial, 5/9.S.L.F. No. 3 same price. We alwaysstock all ORMOND FARTS.

BRITAIN'S FAV.3 (Deluxe)A.W. 6/4/29

Ormond Log .0005, 6/4 .00025, 5/6; 7 -ohm panelRheo 2 6 ; 3 Benjamin V.H., 4/6; ForrnodenserType "J," 2/- .0003 and series clip, 2/-; 2-meg.Leak, 1/-; '14.snewell All purpose H.F. Choke, 5, 9 ;R.C.C. Unit 7/-; 50,000 ohm wire wound,5/6; 2-mfd. Mansbridge, 3/6; L.F. TransformerR.I. Varley, 15/-; (add balance any other), Push-pull Switch, 1/3, complete with Panel Brackets, In-dicator, G.B. Clips, 6 -pin Base, Connecting Wire,Thin Flex, 7 Engraved Terminals, EBONITEPanel 16x8, and 16 x 9 Baseboard.Above Lot 63/0

Tunewell Dual Coil 6 -pin,7/9; Lewcos Short Wave,

C.0 D. 1, 6 20/45 or 40/90, 7,6 extra.

LEWCOSLeweosC.A.C.5,10/6;C.A.C.2012/6; CS P.5, 10/6; C.S.P.20.12/6; P4 to 14, 3/. each; PI6 to22, 4/. each. Touchstone Coils,30/. pair. C.T. Coils, 316, 5/3.Q Coils; Q.A., 15/- Q.S.P.,21 J.;Q.A.R., 21/-; Q.A.A., 15/-;O.S.G., 21!-. All Lewcos Products.

WE STOCKWHOLESALE & RETAIL Bul-gin, Ferranti, Ekco, Amplion,Celestion, Igranic, Lissen, M.P.A.Ediawran, Coscor, Six Sixty Col-vern, Cyldon, McMichael, Watmel,Lewoos, Pular, Climax, Ormond,1.13., l'ye, -Polymet, T.O.C., Du -hiller, Lotus, W.B., Philips, Mal-lard, and all standard components,valves, etc.

RAYMOND'SFOR WIRELESS

27 & 28a, LISLE ST., LONDON, W.C.2Come to LEICESTER SQUARE TUBE.

This address is at the back of Daly'sTheatre. Phones: Gerrard 4837 and 2821

WE ARE OPENALL DAY SATURDAYALL DAY THURSDAYALL DAY EVERY DAYHours 9 a.m. to 8p.mSat. 9 a.m. to 9 p.m.Sunday morning 11-1

QUOTATIONSfor

SETS OF PARTSSPECIAL PRICESon LISTS of 25/ -CALLERS or POST

Don't Forget Our WHOLESALE DEPT. All Lines Stocked.Hours of Business as above.

Send order with instructions.

OPEN WHIT -MAY POSTMAN.INDAY 1 0 t o 1

Orders despatched earliest possible'

TUNEWELL COILSfor MULLARD S.G.P.3Aerial or Anode, BBC crLong -wave, 7/ 10 pair.DUAL C.T. Aerial or Anodewith reaction for CLARION,10/6 each. Trade supplied.Post extra.

Li

Tunewell Dual250/2000 (as shown) 7/96 -pin Base, 1/6Ebonite cut while you wait at/d. square inch, also Jinchat Id. Only the best supplied.Drilled Panels for all cir-cuits. Post extra.

TRIOTRON UNITAdjustfble 4 -pole i7/0

mArm. ( arage Paid .. s

Illustrated Catalogue(144 pages). 1/- refunded on

first 10'. order.

LISSENValve Holders, 1/-; Fixed Con.

ensers, 1/-;1/6; Leaks, lic;Switches 1/6, 2/6; Latent 2 -wayCaro. Vernier, 4/6; Rheostats,2/6; 13.13., 1/8; Liasenola, 12/8:L.F. Transformers, 8/6; Coils,60X, 6/4; 250X, 9/2; II.T.,7/11; 100-v., 12/11; Super 60-v.,

; Orid Bias, 1/6; 4.5, Col.;Super 19/-; Variable .0003,61-; .01101,

GOLTONIE Ultra ShoreWave Coils for Cossor NewMelody, 7/6 pair. Post 6d.

VALVESMullard, B.T.H., Marconi,Edison, Osram, Cosmos,Cossor, Six -Sixty, Det.H.F., L.F. R.C., 10/6 each.Power 12/6, S. Power 15/-,S.G. 22,'6, Pentode 251,TRIOTRON

Det., R.C., 5,''2 eachPower, 6/9. 2-v. or 4-v.

Post 6d. 3 post free).

MULLARD S.C.P. RECEIVERAll parts stocked. The following items ARE ESSENTIALFOR ABOVE, but you can use the others from Master 3 Staror Five P. if desired, or we have them in stock. Full List onrequest. Drilled Panel Aluminium, 5:6, or Ebonite for D.C.Mains, 10, 3. Pair .0005 Log " LB.", 19 .. Pair Drum DialsL. and R., 21/-. Junit Plano B. Board, 2,'-. Cyldon .0003Bebe, 81... Sovereign 50 ohm, 216. BBC Anode and Aerial,9'6. Long Wave Anode and Aerial (Colvern), 10/6. MetalScreen, 10 6. Pair Junk " 14.V." Holders, 36. 3 MullardValves S.G., 22,6. Peptone, 25/-, and one at 10,6.

ALUMINIUM

CRADLEWith fitted 10 in. Float.ins Cone and 12 in.Square Baffle Board.Takes all Bal. Armature

Units.

7111Post 9d. U.K.

GENUINE IDEAL BLUE SPOT.(101) 9 -pole Bal. Arm. completeCRADLE and BLUE SPOT, 30/-.

Adjustable Power 66Kwith Cord, 25j-, orPost Free U.K.

IM. SPECIAL COUPON (72)FOR EVERY 30/. you spend retail

1YOU CAN buy ONE of the following for3d. each extra (on this Coupon)

I1 H.F. Choke, Silk Loud -Speaker Cord, 9.volt Grid i

Bias, Pair Panel Brackets, .0001 Reaction, 2 mfd.:Mansbridge, 100 ft. Insulated Aerial, 4- or 5 -way'

I Battery Leads, 30 ft., Coloured Connecting Wire.i S.M. Dial, 12 yds. Lead-in, Fuse and Holder, 12Nickel Terminals, 60X Coil, Permanent Detector,!Battery Switch, .0003 and 2-meg. Leak, 6 -pin Coilbase, 12 yds. Twin Flex. 100it. indoor Aerial,.0005 Variable, Set of 12 Plugs and Sockets (red orblack), Set of 3 Coil Plugs with Terminals, Wave

:changeI

Switch, .01 Fixed Condenser, 1 mfd.... .2

1

Don't Forget to Say That You .Saw it in t'A.W."-

D.C. Unit (HT) ..Short-wave Adaptor (i v.) ..Universal Short-wave Adaptor ,

Buzzer Wavemeter (6d.)H.T. Unit for A.C. MainsLodestone Loud -speakerJames H.T. Unit for D.C. Mains ..Short-wave Adaptor for Dominions Five

Cgna=Wire kb

BLUEPRINTSCopies of the " Wireless maqvie." andof " Amateur Wireless" containing des-criptions of all these sets can be obtainedat Is. 3d. and 4d. respectively, nog fres.

Index letters " A.W." refer to "Amateur Wireless " sets and " WIC"to !* Wireless Magazine " sets.

All Post Free

CRYSTAL SET (6d.)1929 Crystal Receiver .. AW16;A Daventry-Local Crystal'Set AW185

ONE -VALVE SETS (1s. each)Beginners' One-valver AW 140Reinartz One .. WM127

TWO -VALVE SETS (Is. each)East to West Short-wave Two (D. Trans.)Beginner's Two (D, Trans) Auto Two (D, Trans) ... .All -Mains Two (D, Trans) ..Key -to -the -Ether Two (D, Trans) ..Meteor Two (D. Trans)Clipper Two (D Tram)Twin flex (Reflex)

AW159AWt7tAW174AW t8o

WM1o7WMit4WMi35WM t38

THREE -VALVE SETS (1s. each)All -wave Mains Three (I IF, D, Trans, Rectifier) AW ,44All-purpose Short-wave Three (D, RC, Trans) AW147Screen -grid Q Coil Three (HF, D Tram) .. AWt50All -Britain Three (HF, D, Trans) AW [58Bantam Three (D, RC, Trans) AW 16oHartley Dual -range Three (D, RC, Trani) .. AW166Listener's Three (HF, D, Trans) price 4d. free

with copy of "AThree

. AVV169The Binowave (D, RC, Trans) 'AW 7zClarion Three (SG, D, Trans) AWI75rim Favourite Three (D, RC, Trans) .. ANN 179Everyday (D, 2 Tram) WM5zAll -wave Screen -grid Three (Hid, D, 'Trans) WMtto.Standard Coil Three (HF, D, Trans) .. WMII7Festival Three (D, 2LF-dual Imp.) _ WM t t8 .Wide -world Short -waver (SG, D, Trans) WM1zo

.. WM123

.. WM' 24

.. WM t29WMI31WMi36

.. WM t4t

New Year Three (SG, D, Pentode) ..The Q3 (D, RC, Trans) . Lodestone Three (HF, D, Trans) ..Simple Screen Three (HF, D, Trans) .Dynamic Three (SG, D, Trans) ..At Home Three (D.zRC)

FOUR -VALVE SETS (1s. 6d. each)OverseasShort-way.er (I -IF, D, 2Trans) AW133The Ranger( SG, D, RC, Trans) .. AW145Broadcast Pitture Four 11 -IF, D, 2.RCI AW t63Orchestra Four (D. RC, Push-pull) AW. t 67All Europe Four (a I -IF. D, Trans) .. AW173Stability Four (li.F, D, RC, Trans) .. AW 8z

Q -coil (HF .D, RC Frans). M7Five -pounder Four (FIF,, D, RC, Trans) W

WMqt

Touchstone (HF D, RC, Trans) .. WM tooReyner's Furzehill Four (SG, D, 2Trans) .. WM i izEconomy Screen -grid Four (SC, D, RC, Trans) WM a alBinowave Four (SG, D, RC, Trans) . WM I )9Standard -coil Four (HI, D. 2 RC) WMI24Dominions Four (zSG, D, Trans) .. WMI34The Drum Major (HF, D, RC, Trans)., .. WM t 37

FIVE -VALVE SETS (1s. 6d. each)" Q " Gang -control Five (21 -IF, D, Trans)2 AWt6tEmpire Five (a SG, 13, RC, Trani) WMo6Fidelity Five (HF, D, x RC) .. WM133

SIX-VALVE'SETS (1s. 6d. each)Short-wave Super -6 (Super -het, Trans) AW 67Eagle Six (3 HF, D, RC, Trans) .. WAlio6

AMPLIFIERS (1s. each)Screened -grid HF Amplifier .

A.W." Gramophone Amplifier (3RC)Searcher Unit (HF)Gramophone Amplifier (3 v.)Gramo-radio Amplifier (2v) (Trans.)Signal Booster (HF Unit)Auditrol Amplifier

MISCELLANEOUS (Is. each)H.T. Eliminator for A.C. (zoo v. output) AWtriaL.T. and H.T. Mains Unit (D.C.) AW1z3

iszener's Speaker, price 4d. free with copy of"AW" .. . . AWt70

Arcadian Linen -diaphragm Loud -speaker (Full-.. AW177A

AW 178AW 183WM8z

WMtzt. WM125.. WM126 WM,33.. WM t4o

AW13SAWt 62AW176AW187

. WM7.4WMI28WA4r32

PORTABLE SETSHouse Portable (SG, D, RC, Trans) .. AWt63 1/6Arcadian Portable (SG, 0, 2 Trans) with

linen -diaphragm loud -speaker (half -scale) AWt 77 r16L5.5.o Portable (D.Trans.) AWiSt 1/6Talisman Portable (SG, D, 2 Trans) .. AW184 1/6Chummy 4 (with modifications for LS

and HT) 1/6Wayfarer Portable (Super -het) WM139 1/6

Send, preferably, a Postal Order (stamps over sixpencein value unacceptable) to Blueprint Service

AMATEUR WIRELESS 5S-61 FETTER LANELONDON, LC.4

732

" LETTERS TO ,THE EDITOR "(Continued from page 730)

Rattle in Linen SpeakersIR,-I built one of the above, accord-ingg to your instructions as published.

But, do whatever I could, I could not stopa certain amount of rattle. So, concludingit was impossible to get an even centretension from a square frame, I decided toexperiment as follows. I took two 5 -plyboards, 24 in. square, and cut a circle inone 20 in. and in the other 15 in. I thenglued the linen dead tight across the wholeof the boards, and then doped it andmounted them up as per your instructions,with just the 6 -in, bolts connecting thetwo boards. The result is simply perfec-tion. Several of the wireless fans about.this neighbourhood have seen it, andbefore long there will be plenty of themabOut here. I got the first benefit of thattype of speaker from you, so am glad topass on to you my idea for the benefit ofyour readers.-J. L. (Poplar, t.).

TRADE NOTESESSRS. FERRANTI, LTD., advise

INA us that in future all audio -frequency!and output transformers manufactured bythem will have their primary and Secondaryterminals reversed from what has hithertobeen their standard positions.

Mr. J. H. Thomas, M.C., M.I.E.E., hasrelinquished his position" as AssistantManager of the Mavhester branch of theGeneral Electric Co., Ltd., and has taken'up the position as General Sales Managerof N.C. Cossor, Ltd., of Cossor House, High -bury; London, N.5.

Peto Scott Rover Portable Receivershave evidently proved so popular thatcertain individuals visited the showroomat 77, City Road, at 6 a.m. on a. recentSunday morning, with burglarious intent.,The attraction was so powerful that thefeaf of the" law proved to be as unavailingas the plate -glass window, through whichthe enthusiasts were irresistibly. drawn.

Messrs Peto Scott Co., Ltd. wish to pointout that the easy way is still through theirdoors !

"Amateur Wireless and Radiovision." PriceThreepence. Published on Thursdays and bear-ing the date of Saturday immediately following.Post free to any part of the world : 3 months.4s. 6d.; 6 months, 8s. 9d.; 12 months, 17s. 6d.Postal Orders, Post Office Orders, or Chequesshould be made payable to " Bernard JonesPublications, Ltd."General Correspondence is to be brief andwritten on one side of the paper only. Allsketches and drawings to be on separate sheets.Contributions are always welcome, will bepromptly considered, and if used will be paid for.Queries should -be addressed to the Editor, andthe conditions printed at the head of " OurInformation Bureau" should be closely observed.Communications should be addressed, accord-ing to their nature, to The Editor, The Adver-tisement Manager, or the Publisher, "AmateurWireless," 58-61 Fetter Lane, London, E.C.4.

MAY 18, 1929

PREPAID ADVERTISEMENTS.Advertisements under this head are chargedTHREEPENCE PER WORD, minimum chargeTHREE SHILLINGS.

DEPOSIT SYSTEMAs the Publishers cannot accept responsibility for the

bona fides of advertisers in this publication, they haveintroduced a system of deposit which it is recommendedshould be adopted by readers when dealing with personswith whom they are unacquainted. It is here explained.

Intending purchasers should forward to the Publishersthe amount of the purchase money of the article advertised.This will be acknowledged to both the Depositor and theVendor, whose names and addresses must necessarily beglven. The deposit is retained until advice is received ofthe completion of the purchase, or of the article havingbeen returned to and accepted by the Vendor. In additionto the amount of the Deposit, a Fee of 6d. for sums of 11and under, and Is. for amounts in excess of £1, to coverpostage, etc., must be remitted at the same time. In casesof persons not resident within the United Kingdom, doublefees are charged.

The amount of the Deposit and Fee must be remittedPostal Order or Registered Letter Cheques cannot haaccepted), addressed to

"AMATEUR WIRELESS," ADVERTISEMENT DEPARTMENT,58/61, FETTER LANE, LONDON, E.C.4.

PA'IENTIL-Trade Marks, Advice Handbook free.-B. T King, Regd.Patent Agent, 146 Queen Victoria Street, London.

EASY TERMSWe specialise in the supply of all good -quality RadioApparatus on deferred terms. All weP-known kits ofparts, components and sets, now supplied from stock.LOWEST TERMS. Send List of requirements to

LONDON RADIO SUPPLY CO.11, OAT LANE, NOBLE STREET, LONDON, E.C.2

Phone: NATIONAL 1977

WET H.T. BATTERIESToles all R.T. troubles

SELF -CHARGING, SILENT, ECONOMICAL/ARS (wazed) 21" a 11" eq. .. 1/3 doz.Zmos, New TYPO, 101 dos. SACS 1/2 doz.Sample doe. (IS volts), complete with bandsand electrolyte 4/1, post 9d, Semple salt,Bd. Illustrated booklet free. Bargain kit ,rec.AMPLIFIERS, 30/. 3 -VALVE SET, £5.A. TAYLOR, 57 Studley Rd.,

Stockwell, London.

WIRELESS CABINETSMAKE YOUR OWN

Send stamp for Free catalogue and pricelist.

WOODWORK, 199 HIGH ROAD, LEE,LONDON, S.E,13.

50/- as shown

LOEWE RAD4 Fountayne.Rd.,Tottenham. N.15

AtilaancleALL MAINS 2 and 3 VALVE SET for £1 deposit.Balance £1 a month. Write for free Illustrated List.

WORLD'S WIRELESS STORES,Wallington, Surrey

44 WIRELESSMAGAZINE "

The Big British Wireless Monthly

1/,COUPON

Available until Saturday,

MAY 25th, 1929

.fbeisnai

MAY 18. 1929 Ctr. ateur yv'truft)

WA EA 11°COMPOA/EA/TSTALISMAN PORTABLEMr. L. A. Chapman has designed this special coil onentirely new lines. Two windings are arranged in parallelfor medium wavelength reception, but for long wave-length reception only one winding is used, the two halvesof the medium wavelength winding being left "dead" ateach end of the long wavelength winding. This intro-duces just enough damping to offset any tendency tooscillation, when working on the long wavelengths. Thearrangement of the switching permits retention of thecentre tapping whether switched for medium or longwavelengths, so that the coil can be used in either atapped tuned -anode circuit or in a plain tuned -anodecircuit. PriceThe Chapman Dual -range Coil isspecially designed for use with

screen -grid valves 7/60 (2r V, E A N IT I!: Components suitable for this

Receiver are:Battery Switch (on and off) G22 1/ -Wave Change Switsh (3 way) .. fibScreen, per pair .. 6/ -

WRITE FOR NEW LISTWRIGHT & WEAIRE LTD., 740 HIGH ROAD,TOTTENHAM, N.17 Phone : Tottenham 3847 and 3848

110101901100010911111,11/111111111,1111RIWOWOMP

FLOATING ACTIONVALVE 1101DEIR

SELF LOCATINGC.F.&11.BurTori PROGRESS V/K5.VIALSALL

RUPERT COLLINS SERVICE

To Ensure Speedy Delivery;

:SAFEGUARDINGyour setis guaranteed

DUBILIERCOMPONENTS

breakdownsby using

against

,,,,, i ,, TOROID H.F.,t / TRANSFORMERS

A complete rangeof models, coveringa wavelength bandof from 22 to

2,000 metres.

from 10/6 to 15 -

..tea

,,

fr'' )

MINICAPD.P.D.T. DUCON ( ,,1! "N. .'.

AERIAL ,

SWITCH For use on nlcc-

5 6 tric mains.A1K,lutely safe. 5, -

NEUTRALISINGCONDENSER

zFor baseboard imunt- 1.4'..

ing. Maximum capaci- -f , -L............L.......,_ty, so micro - micro -

farads.

. 3/6If unobtainable from "TOREADOR SCREEN -GRID FOURyour dealer, write This set incorporates the latest develop -direct to us giving ments in Receiver design --full construc-

his name and address. tional details free en request.

UBILIERADIO PRODUCTS

OJ ,,,,..,

4<G, MP I." mar.0

Dubilio Condense, Co: (192.3), L41., Durnq Wc ks , I -:-?:via Mad, N. Ac ion,London, W.3. ' .. (0 2 .3q S

Mention '.41.W." to Advertisers

ivMAY 18, 1529

0

Arai ley

Wits:ONG SHOP, OVER100 GIRLS F..MPLOYE0IN THIS SHOP ALONE

Saafinee SHOP

Qt1T5IDE VIEW OF 'ION OF WORKS

for comingbig radioI developmentsThe Var' organisation- rich in radio experience

and source a score of well-known inventions- ison ' the threshold of big developments which willmake the -name VARLEY for ever famous in radio.

More than £ re,000 has just recently been spent onthe purchase of -.e-plant and in enlarging ourFactory in South East ion. The famous Bi-duplexwinding, first inventec. us some 3o years ago, hasreached perfection; and this is only one of manyspheres of Varley activity. in which the valuableexperience gained is being applied to the prochiction ofmany other components. It is interesting to note thatin x922 the coils for many of the well-kii-own L.F.Transformers 'of that day were VARLEY.

-And as in the past the new products of this Varleyorganisation will in a very few weeks time be theadmitted STANDARDS of efficiency and reliabilitythroughout the length and breadth of the British Isles.

arley

Aduerlisement of Olirer Control 41d., Eingszzay House, t 03 Ein;:-.7.tay, London, W.C.z. Telephone : Holborn 5303

-3,P;Inted in England. Published by Bernard Jones Publications, Ltd.. 58/61 Fetter Lane, London. E.C.4Sole Agents for South Attica: CENTRAL NEWS AGENCY, LIMITEC: Sole Agents for Australasia: GORDON & Goriu, LimiyEn.-Saturday;lday.-48, :91).

Every oz1 Thursdalik) - World Radio History

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Transcript of Every oz1 Thursdalik) - World Radio History