Repair and Restoration of Antique Radio Equipment

1 Repair and Re storation of Antique Radio EquipmentbyGregor y L. Char vat, MIT Lincoln Laborator yforMIT Haystack Obser vator y Open LunchOctober 21, 20091 Wednesday, October 21, 2009 Antique Radio EquipmentLooks coolUnique sound qualit y1930-40 s jazz sounds be t terFunctional histor yLe arn how things were made2 Wednesday, October 21, 2009 OutlineStep-by-step proce ssCase study: Hallicraf ters S-76 (1951-54)Case study: Colin B. Kennedy Model 20B Console Radio (1929)Summar yHallicraf ters S-76 Colin B. Kennedy Model 20B3 Wednesday, October 21, 2009 Step-by-step proce not power up your Radio ! ye s, it doe s not work more harm than ser vice all electrolytic and paper anything that looks damaged (burned or exploded) y Radio (wear safe t y glasse s) trace through circuit, replacing resistors where will work e xploded vie wwax-papercapacitor4 Wednesday, October 21, 2009 Hallicraf ters S-76 Amateur Radio recei ver 1951-1954 2 conversion he terodyne architecture 11 tube s 538 Kc - 32 Mc CW, AM, SSB (with ste ady hand) 41 lbs De sign based on SX-28 (widely utilized during WW2)FrontTop insideBot tom inside5 Wednesday, October 21, 2009 Hallicraf ters S-76.

2 Capacitor spe wing waxPowered up S-76 without replacing electrolytic capacitorsone elect rolytic smoked and spe wed waxcathode capacitor on AF power output tube was shortedReplaced 2 paper capacitors that looked rough No other caps replaced, keeping Radio original6-e7loNof,d_9dMs_9duws-tamuoN-ed vow-lqvoualscNgobgs qJUAsI NOIJISd NNeoss gJrns rll^rtoslssedrz6tG,3J{301f,OIISM NAOHS NJUrgexe@rndrno E3rcdf)l OS :llf){ O99l -llrcssCgvsg@tNslz rt3s6 Dcap replacedne w caplocation of cap6 Wednesday, October 21, 2009 Hallicraf ters S-76: signal tracing'5lueuelnsDeu a60110^ ro, Po! lou6!s ou'unulxou lo lorluoJ ganlo^'t6urpoel eturlsrrol puo o6ollo^u! %9t+ ,o uollolro^ o slqFiod telDusonlo^ luouoquot uo eruolalol louruoN'rOu!pDer e60110^ro, sllo^ lll lD Poulolulpu o6 Dllo^ eull'e^Io6au uouuotol uld lelros uort !ro senlo^ $oq 50 uaoqr eiD suoFeuuot loltos'su'{o 000' lto ^ )v lllo^ rad r@rloOOO'OZ tD ero ^ )O' NO NI TICJLIIs USIINII NO NI HCTLI\S CAV'I qVOUS Nl IIC,LLIIS 'II JO 8 NId rIOUJ qSUnSVSrrt +'NOIJIS!}}}

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4 NVS-0e oNvq-?I dvs-tgJNtnqts asNOIUSOd I qNVqM NAOSS HJUAS qNVglcse@@LLl\,' ffi.!l"YY-norrw:gr "lr!,ffirIIIIIIIIIIIIIIIIIIIIIIIIIiIIIII Id6o'c +QO)^o v'(UooooRFLOIF signal tracing and bias measurementstube bias chartSignal generator connected to RF inputSignal traced using 10x probeSignal stopped at front-end mixer tube V2had to check the voltage s on the tube pinsvoltage chart included in all ser vice manualsrequire s proper impedance volt meter, 20K/volt Simpson 260If the voltage is outside of +-5% then replace the re sistor(s) soldered to that pinold carbon resistors INCREASE in value with ageR17 and R18 had to be replaced (and others)7 Wednesday, October 21, 2009 Radio started to workPerformed alignmentst raight-for ward procedure in manualTe sted Radio to full sensiti vit y specificationSucce ss! Long wire antenna; listening to amateur Radio stations and many short-wave wc luauaaoJdul JequnJou Inun II pu" 0I sdels l"odou'uollJalJop unulnu rot lsntpvazYJ)Io0tJXo09'uorlreltap unurxBu roJ l8n(pvtzv'Lz\'9 ZVJ)I00''Tc}I00tl'ep"uaq wc luauaaordul Jarnrn]ou ltlun 6 pu" g sdals l"edau'uo!

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7 Pwq,, ol rolcelospu"q o{l pw 'WV ol qcllds nv/llC .,,aalacoJ,, ot qcllN oalacal-puos .,,IJo,, 01 saqcllAs Cl\V p@ JaIIEII aslou or0 uJnI'ou!I rapq IBIp arl| Japun alBcs Sqttol ar0 do oraz or0 las pu" pasolc {IInJ 3u"3 Auluq urnl IsIp los oJINIWNCnV CNuJT|N rddi:lllnilx,fj dvlt-cNoillnxrcNl'II0lo' 'oHallicraf ters S-76: alignment8 Wednesday, October 21, 2009 Colin B. Kennedy Model 20B AM broadcast band recei ver 1929 TRF architecture 7 tube s phono input unrecognizable parts f rail cloth wire s Globe tube sFrontTop insideBot tom insideRe ar9 Wednesday, October 21, 2009 Model 20B: Re-cappingReplaced all elect rolytic and paper capacitorsRe sistors and some capacitors are ne arly unrecognizablePaper capsSprague Midge t cap, with nast y bubble s coming out of itPower supply capsBot tomTop, lef t-sideUnrecognizablere sistors10 Wednesday, October 21, 2009had to replace cloth cordinfamous for electrocuting Antique collectorsutilized 3-wire computer power cordgrounded chassis for safe t yadded 3A in-line fuse for fire protectionold cloth and organic rubber wire s crumble e asily when strainedprotection against possible future shortsModel 20B: safe t ybot tom, after restorationadded.}}

8 3A fuseadded: grounded computer cord11 Wednesday, October 21, 2009 Model 20B: poor documentationCourtesy Nostalgia Airmy Radio has a single-ended audio output stange with one pentode, model 247 rather than a pair of push-pull triodes as shown herecathode bias resistors in the RF section on my Radio are , not 3K, 3K, and 5K as shown hereDifficult Restoration : only remaining schematic doe s not match what is in the radioRegardle ss of this, it was a succe ss. Listened to the Red Sox game, first time in decade s that this Radio has tuned in a ball , October 21, 2009 Problem: ver y lit tle music on AM bandFe ature: phono-input tied directly to grid of de tector triodeIPOD wired directly in1920-40 s jazz playlistpodcasts; talk Radio that you want to listen toModel 20B: IPOD docCourtesy Nostalgia Airmy Radio has a single-ended audio output stange with one pentode, model 247 rather than a pair of push-pull triodes as shown herecathode bias resistors in the RF section on my Radio are , not 3K, 3K, and 5K as shown here13 Wednesday, October 21, 2009 Summar yInstant conversation piece Re al radios glow in the dark, anonymous, generally accepted philosophy in Antique Radio communit yUnique sound qualit y for your vintage jazz collectionPotential for upgrade.

9 IPOD doccelebrating 29 CBK s 100 th birthday soonRe source s:e xpert advice: w w s and parts: w w information about the se radios: w w ~gr20603 click on Re storation S-76 or 20Be-mail me with your que stions: gregor October 21, 2009