Julian ROS5'nick1012 Tyson Aven uePhiladelph ia PA J 911 1

The IG-102 Goes Transistor!

- tubeless portability for this Heath signal generator

T he Heath IG-l 02 radi ofrequency signal gen­

erator is a versatile general­purpose wide-range inst ru­men t o f co n ve n t io na lvacuum-tube design whichha s been catalogued fo rseveral years. For those whohave acq uired the IG-l 02 inthe past and those who arestill looki ng for a good signalgenerator at a mode ra te price,th is article provides a simple,economic, and fast means ofco nversion for portabilitywith o ut sac r i f ici n g theoriginal qualities. Modifi ca­t ion of the IG·102 gives theinst rument new ca pabilities,as foll ows:

1. Batt er y o pe r a ti o nut il izing either dry ce lls or anicke l cadmium rec hargeablebank capable of su pplying 7to 9 volts at a maximumcurrent of 10 to 16 mA o

2. With t he use of re­chargeable nicke l cadmiumcells of approximately 1.2volts per ce ll, 6 to 8 cells aresu fficien t to provide the re­quired o perati ng supply vol t ­age. The basic radio fre­quency circuit will operatewith a minimum of 4 voltsthrou ghout its frequencyrange. For charging purposes,a self-co n tained battery-

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charging circuit is used whic hemploys the o rigina l compo­nents (t hese can be dispensedwith if d ry ce lls are in­stalled) .*

3. All tube sec t ions a rereplaced by four fi eld effec ttransisto rs, such as thoseavai lable from Radio Shac k ­#27 6-1623* * - or Catectro- # K 4-634_

Procedure fo r Modification

The followi ng step-by-stepinstructions apply to changesand additi ons to the basicIG-l 02 radio fre quency signalgenerator. Accordingly, theoriginal instruction manualand d rawings are used forreference to detail th e modifi­cat ion procedu re . This pro­ce d u re invo lves sim p le

• Installa tion of the batterysupply is simp le , si nce th ere isample chassis sp ace available t omount battery brackets for ac­commodating the battery u ni ts.

•• Some o f these Radio Shack#276-1623 pac kages c ont ain as­sortments o f bo th rf and af fieldeflect t ransistors. In testing them ,the af types w ill not oscillate. Oneparticula r type which respondswell a t radio frequ enc ies is the2N59 5 1. The white-black t ypesare af and do not oscilla te at radi ofrequenc ies; also, the metallictypes are unsu itable .

changes, installati on o f newcomponents , and construc­tio ns. Before undertaki ng themodifications, 1 advise thatyou s p e n d so me timest udy ing and reviewing thebasic circuit and assembly tobecome fam iliar wit h theo ri ginal layou t . Add itio na ll y,stu dy the detai ls of the fi eldeffect transistor connect ionlead designat ions. In the asso rtment p rovided in RadioShack's #2 76-1 623, threetypes are referred to in thedesignation of leads. Withreasonable ca re, th ere shouldbe no difficul ty using any ofthe t ransisto r t ypes.

1. Refer to Fig. 1, a copyof th e origi nal circu it.

2. Remove all t ubes, if theset has at ready been con­structed.

3. Unsolder and d iscon­nect power transformer con­nect ions (filament supply linean d high-voltage rectifier­filter system), and recon nec tthe power supply compo­nents as shown in Fig. 2,usin g additi onal compo nentsas needed .

4 . Solder a 75-0hm,Yl""Watt ca rbon resisto r ac rossthe R2 (33k, 2 W) decouplingresisto r used in the o riginalcircui t.

5. So lde r a 90·0 hm,Y}-Watt carbon resistor acrossthe R6 (4_9k, 2 W) de­coupling resistor used in theorigi nal circui t.

6 . Spot so lder o ne radi ofrequency field effec t tran­sistor ac ross tube socketV1B, te rminals 1-2-3, usingthe lead references given int he tr ansistor package tnstruc­tio n shee t. However, if tran­sistors are selected from theBctranslstor assortment giveni n Rad io Shac k's packet#2 76-16 23, t hen lead orienta­tion should be followed asper t he drawing supplied int he packe t.

To mou nt the t ransisto ron the tube soc ket, do thefollowi ng: Hold each leadwit h long-nose pliers (fo r aheat sink) as solder is applied.Use a 35- to 40-Watt penciliron with a small blade tip1/8 " wide, and solder alloy60-40. Apply a small drop ofsolder to the end of eachlead. Afte r thinning the leads,spread th em to matc h thespaci ng of the Jugs on thetube socket. Ap ply eac h leadto the required tube socketterm inal , as designa ted above( t o facilitate con nections,also apply fresh so lder to the

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Test, Operation, and Adju st­ment

1. Before applying batterypower to the circu it, checkthe positive-to-ground resis­tance to make certain thatthere is no short c ircuit orabnormally low resistancereadi ng due to a defective

permit external testing of thebattery supply (+) and (-).

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be more convenient formaking connections to turnthe transistor over (rou ndside up ) and cross the D an dG leads ( u se insulatedsleeving).

Step #9 completes themodif icat io n conversion ofthe basic IG-' 02 rf signalgenerator. Additionally, I in­stalled rear t ip jacks with thecircui t connect ion leads to

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minals when soldering. Carein soldering and applying thetransistor leads wi ll insuresuccess and avoid thermal ormechanical damage to thecomponents.

7 . Foll o wing the sametechnique for soldering asexplained in step #6, applyand connect another rf fieldeffec t transistor across "thetube socket 1A, terminals 6,7, and 8.

8. Apply and con nect thethird rf field t ransistor totube socket 2B, terminals 6,8, and 9.

9. Apply the fourth fieldeffect transi stor to tubesocket 2A, terminals', 2, and3 . ( If another type ofFET t ransistor is used, makecertain that the proper tran ­sistor leads are used to makeconnections.) Again, it may

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leads, a slight bend on thewi re ends will help in makingsurface-to-surface contact fo rsolde ring. With the pliers,hold each lead against thesurface of the required tube­socket terminal , and applythe iron to the opposite sideof the terminal until solderflows well to form a goodspo t - s olde r joint. Nomechanical co nnect io n isnecessary to co mplicate theprocedure. Once the firsttransi stor lead is so ldered, itwill make the transistor self­support ing, and the remainingsolder operation wi ll be easilyhandled and completed.Remember to use the long­no se pliers as a heat sink for" pushing" the transistor leadsagainst the tube socket ter-

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Fig. 3. Modified IG- I 02 circuit. TlA , TlB, T2A, and T28 - fourrf FE Ts equivalen t to Radio Shack package #276-1623 orCalectro #K 4-634.

component or wiring co ndi­tion. Rotate the bandswitchwhile checking the resistanceto ground (which should beseveral hundred Oh ms, atleast).

2. Insert a milliammeterin series with the battery, andcheck the direct current onall bands, which should be 7to 15 mAo Switching in theaudio to ne oscillator-modu la­tor will increase it about 1rn A.

3. Rf out put. A diodedetector rf voltmeter appliedto the high end of the fineatte nuator cont rol (turnedco untercloc kwise for mini­mum rf output) should indi­cate about 1 to 1.25 volts onband "A" (low-frequencyend), and, on each successiveband, it will drop off pro-

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gresstvelv. Never th eless, rfout put should be detectabl eon all bands.

Vary the tuning on eachband fro m low to high end ­the rf voltage should varysmoothly (usually decreasing)without the sudden jumps orfalloff usually assoc iated withparasi tic absorption con­ditions.

4 . Audio tone oscilla tormodulator. The ac output ofthe audio tone oscillator , asmeasu red across the audioou tput control , should be 1to 2 volts. Check th e tonefrequency with a pai r ofheadphones co nnected to a0 .1 uF co upling capacitor.Finally , use an allband re­ceiver or grid-dip meter , ifavailable, to check th e rf out­pu t frequency. The frequency

response in each band shoul dbe within a few percent an dnot need any alignment ortuning adjustments.

Heterodyn ing with broad­cast stations will show excel­lent frequency stability. Onband " F", use an identifiableFM station to spot check thefrequency calibration in the88 to 108 MHz range. I foundit necessary to "squeeze" therf co il to about one-half itsorigi nal length to get goodfrequency alignment. Use thelong-nose pliers to squeezeturns. To check against anFM stat ion, turn the audiomodulation on, connect therf cable, and bring it near theFM receiver's vert ical an­tenna. A good clean modula­tion note shou ld be heardwhen the signal generator

passes through an FM station.

Conclusion

I modified the original err­cult by converting to thebattery-operated solid statedesign, as described. In addi­tion, a three-crystal oscillatorfrequency-spotting standardwas installed with a productdetector and audio amplifierspeaker section. This co mbi­nation provides freq uencychec k intervals of 100 kHz,1.0 MHz, and 10 MHz, fors pot-chec king the interna lsix-band vfo or for externa ltesting. Usin g the crystal stan­dard , he terody ne testingshowed excellent frequencytr ac kin g a nd calibrat ionthrough the six bands. Si ncethere is ample chassis spaceavailable, the three-crystal

Fig. 4. TR4-TR10 - Radio Shack #276-2039 or equivalent; TRI I - auat-oate MOSFET; cn- Area 309 padder; CT2 - Area 306 padder; CT4 - Area 465 trimmer; L1 and L2 - d e; L3 ­20 turns #30 enamel wire on 2 W, lOOk resistor.

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t ernall y as a subun it.Heterodyne activity can bedetected up to the 50th har­monic . With addi t ional wave-

frequen cy spot circuit is leftoptional and is merely sug­gested to you. For this pur­pose, in a more extendedproject, three crystals andoscillator design data can beobtained from Jan Crystals,2400 Crystal Drive, Ft.My ers FL 33901. A ddi ­tionally, a dual-gate MOSFETproduct detector, a 250 mWintegrated audio power ampli­fi er, a min iature volume con­trol, and a 2%" loudspeakercan be com bined to prov idethe desi re d freq uency­spo tting funct ion.

Fig. 4 shows a circuitwhich incorporates the addi ­tional features just described- a th ree-crysta l osci lla torfrequency section with aproduct detector and anaudio power amplifi er formonitoring the heterodynereactions between crystal fre­quencies and the vfo spec­trum. The entire unit can beeasi ly and convenientl ymounted in the rf signal gen­erator chassis assembly orsepar at ely assembled ex-

New Productsf rom page 60

($15.95) way of quickly learningand appreciating the advan­tages of the solderless bread­boarding approach.

The PB-6 Proto-Board Kitcomes complete with a pre­assem bl ed breadboard ingsocket , tw o preassem ble dsolderless bus strips, four flve­way binding posts, a metal

ground base plate, non-marringfeet, and all required hardware.When complete,l ts si x hundredthirty tie-points permit flexibleconfigu rations of as many assix 14-pln DIP ICs.

Despite its low cost, the PB-6provides a ver y confi dentbreadboarding base. Of thelour binding post s, one Isgrounded to the ground basepla t e, permittin g h igh

esc Proto -Board 6.

The Palomar PTR-130K transceiver.

d istributed capac itance andlow distributed inductance forenhanced high·speed ci rcui toperation. The three remainingfi ve-way binding posts can beused to interconnect the c ircuiton the PB-6 to power and signallines and the outside world .

Follow ing the easy assemblyinstructions enclosed, uSingonly pliers and a screwdriver,assembly time for the PB-6 Isless than ten minutes.

For further information, con­tact Continental Sp ecialtiesCorporation. 70 Fulton Terrace,Ne w Haven ';T 06509.

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