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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
tube-socket terminals).In spreading the transistor
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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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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