SpecialIssue: A Tribute to AveryFisher and The Fisher Line of Tube Receivers

• Editor's Page / Tube Industry News 2 In This Issue Fishn$00 Fftmilyo fR eceivers • Fisher 500 � The Start ofa Generation 3 • A Tribute to AveryFisher 10

Design, Historyand Restoration • Book Review· "Tube Lore" 12

6$$0 IJruJKT88 - ThePOtlJet Kings • neRmuWlAmplijier P",!ject I4 Comparisons Between New and NOS TJpes • Story of the Loftin . White 17

• Tbe Power Kings - 6550 and KT88 21

• The Audio Test Bench· Oscilloscopes 25

• UncleEric's Dumpster - Type 5687 31

O,,-!hte tube audio buy/sellwallt ads, librtlly of articles, li"ks to other tube web sites aftd more. www.vacuumtube.com , E 0 I T 0 R S P A G E A N 0 I N D U S T R Y N E W s

Svetlana Announce5 New J'coducl$ U$S550 and th� AV52B SL will be US $750 Editor's Page and Industry each. For more information contact: Svedana Electron Devices has inuoduced Pe,er Q>xm,up News its SV572 series of l2S-wan power !riodes for Audio No,� UK Ltd. high-end audio amps. This series is available by Charlie Kittleson, Editor Uni, C. Pe.cock Ind. with mu of 3, 10, 30 and 160 for a variety of E."a« L)"onCIas

VACU UM T U B E VALLEY I SS UE # 6 • GOLDEN ERA F SH E R 5 0 0

you had 10 do EVERYTHING YOU NEED - ON SUit SUPERB CHASSIS! The Fisher 500 Family of was 10 add a Receivers - The Start of a fCwrdplayer Generation and a loud­ speaker and E FISHER "SOO" you had a A. "'«.... ·.. ".,".i l� FM·AM '.nc,. By Charles Kitdeson _.rid.... }O. " .",.,UIIo ••• M•• pl t gh­ n . wm e c hi .wl., control <08'" -.u tHoit, "" "". fidelity system �_, �! Si"",!, odd •_ plo"" � """""",,,hr. UIII .. ca.. Ly .. The Beginnings of the Fisher 500 for your home. oIw,.,.,"" .. _""",kl< _,,,. .,(IJ.1Jty •• H... 1ot)'O'l' _. Lh _My-m "'" The 500 was a _ FLSHERlJ'1W;btiooa. It> .,.,. .... _ _ In the fifties, the hi fi hobby was con­ '" <�y Fisher in every "'" ,;mel<» I>cauor sidered an expensive proposition. A 1957 "1('''('''0101 sense of the .... --_. .._ . _...... home hi fi set with all thc: bells and whis­ ....- ",.. , _ ... .., --- -­ word,meaning Ior __ ,_, __ tles could set you back $1000 or more in ___ - T _-- excellent � 19505 dollars! Most of the: popula­ I!"..... � ;,:.':.!:. :� !"�""':-o::::'i:: US esig build­ -, ... _ .. _. ",- ..... d n, ..,...., ...... -... -.-- . tion (95%.) did nOI have Ihal kind of .. _.-I...... "",fT,, ".. .. -...... " .. -_ quality and per­ . ...- ...... money to throw around. They were busy formance . [tS rearing the millions of Baby Boomers styling was FM _ AM MASTER AUDIO CONTROL AMPLIFIER populat ing the coulltryside. For most spectacula folks, a or a comhirmion r with a die-c;lM brushed-brass faceplate turers introduced stereo components with , phono, TV console pro\lided the and escutcht-on with tuning meter and tWO complete on one chassis. home entertainment. Component hi fi function lights. Hartnan-Kardon, Pilot, H.H. Scmt and was for rich bachelors, doctors and engi­ many others also introduced stereo neers who had the spare change and lime The 14 tube circuit featured dual rcc­ FM/AM receivers. The catch is, they 10 hook up all thl' cables and fine-Iune tifiers with a 6X4 for the IUner section weren't really FM stereo multiplex units the set-up. and a 5V4G for the 30 wan outpUt stago;, because that system wasn't developed yet. featuring the excellent Mullard EL37 OUt­ For a shOT! time in the mid 10 late 1950s, Avc:ry Fisher, who gOI his start in the pUt . LaterTA500s used 5881 s. however, there was a system of broadcast­ la It: 19305 by manufacturing high-quality Original spe<'ifications touted uniform ing stereo with one channel on AM and radio and phonograph setS, was JUSt get­ response from 16 to 32,000 cycles. Audio the OIher on FM. It was available in lim­ ti n his stride in 1956 with a very corn­ controls included a \'olume contro!, con­ ited areas and was troublesome. Most pre! lcnsive line of amplifiers, preampli­ rinuously variable bass and treble, a four­ tuners and the time had an fiers, tuners, integrated amplifiers and re{:eivers of position loudness Contour connol and external multiplex adapter jack on the package hi fi consoles. Fisher cornpo­ function selector. There was a tapc chassis for ,he future date when the FCC nems were considered by musicians and recorder output :lIId playback preamp­ would standardize stereo FM or for use engineers alike to be the finest available equalizer, four inputs, OUtpUt impedances with SCAmultiplex adapters. in their respective catq;ories. Fisher, as of 4,8 and 16 ohms. The 500 is a mono well other audio manufacturers of the a.s receiver, but S!ilI fealUred a muhiplex All the L'Olge in the late 1950s, stettQ time, used symphony musicians to audi­ detector-out RCA jack for use with stereo LPs needed twO amplifiers to get the Tion and critique (heir new products. adapters which beeame available with stereo effe{:1. A large number of audio­ The goal was achieve the mOST life-like to standardizalion of the FM stereo broad­ philes rebelled against the stereo system. and natural reproduction by using the casring system in 1961. The FM section They claimed that it was a conspiracy ears of actual professional musicians. featured three IF stages and tWO limiters. between the record companies and tbe hi Since the early beginning� of Fisher, fi manufacturers who could now sdi a lis­ many of tbe worlds most prominent and For a mono receiver, the 500 has no tener tWO amps and TWO speakers instead powerful people, including US presidents equal. I personally own one tbal has of one each. Hi fi manufacturers decided :md foreign beads-of-state, owned Fisher been my bedroom radio for years. I COIll­ 10 appease the mono perfectionists with gear. Fisher truly was the standard all pletely restored it with new electrolytic high power amps including the Fisher others had to measure up to. , new signal and bypass capaci. 200, and elaborate mono preanlps such a� tors, new tubes and an alignment job. the Fisher 90C. Their thinking was that Wha, was missing from the Fisher The AM performance is incredible most consumers would Opt for an all-in­ lineup was a complete am/fm wner because the 500 is very sensitive (3 one hi fi recei"er because the mess of amplifier in onc compact package. Other microvoltsl and has exce!!em signal·to. and complexity from sepaL'Olte com­ manufacturers, including Harman­ noise ratio. FM performance is equally ponents was a nightmare for all but the Kardon and Suomberg-Carlson had impressive and very musical with a 1 most possessed audio bugs. illlroduced hi fi receivers in 1954, but mictovolt sensitivity rating. The TA500 they didn't have the Fisher allenlion to is probably the ultimate tube hi fi table Early Fisher Stereo Receivers: TA600 detail and that Famous luxurious Fisher radio. TheTA500 was made from 1956 and 500S sound. through 1958 and is nOt commonly seen In late 1958, Fisher introduced the anymore. Production figures are nOI In late 1956, The FisherTA500 TA600 FMfAM receiver ($349.50). It known, but at le;lst30,000 TA500s were ($249.50) receiver was introduced. It was the hit of the San Francisco and Lo� was -everything you need-on one superb probably made. Angeles Hi-Fi shows. TheTA600 was the chassis. �The TA500 featuredan extreme­ The Beginnings of Stereo first complete stereo FM/AM receiver, ly sensitive FM-AM tun er, a powerful 30- with tWO 20 wan amplifiers wilh a fre­ P watt amplifier, and :1.11 audio comTol cen­ With the advent of slertQ L records quency response of 25 10 20,000 C)'c!es • ler- all built on onc compaCt chassis! All in 1957 and 1958, almost all manufac- or- I db. It had separate tuning indicators

V A C UUM TUB E VA L LEY ISSUE .6

• GOLDEN ERA F SHER 500

and from-ends for both AM and FM. The 600 had a IOta] of 22 tubes and a selenium for DC on the pream­ plifier filaments. It used {he newly inuo­ ducc:d 7189 OUtput tubes in push-pull configuration. The 600 is Ihe only Fisher stereo receiver with tube rectificadon, a 6X4 for the tuner and 5AR4 for the amplifier sections. There were dual eye tubes for indicating signal strength and center-of-channel for both am and fm.

The SooS FM/AM receiver ($324.50) replaced the TAGOO and was only made in 1960 and 1961. It was very similar 10 the TA600 except that il used solid-Slate rectification instead of tubes. The

FM tuner sensitivity was improved 10 0.9 microvoh for 20 db sIn ratio with a 72 ohm amenna. The FM frOnl end fca­ TA500 tured three IF stages and [Wo limiters. The stereo master audio conuol had distortion of .5% and hum and noise at - From serial numbers 20,000 and on, twenty controls and . There wcn� 85 dB. The Power supply was silicon (he 500C was the first stereo recci,·er to nineteen tubes including two signal indi­ recrifier with DC on the low-level audio use the newly developed 6CW4 Nuvi$[or cator tubes, three and twO silicon stage filaments. Golden-Synerode rront end which afford­ . The OUtput stage was rated at ed higher sensitiviTY, a wider overload In 1963, after spending millions of 22.5 wails music power and used push. margin and beller noise rejection. The dollars and eigh years of research on pull 71898. t low-noise 6CW4 triodes, used

500S receivers are relatively scarce and were not even listed in Allied Radio or LaFolyeue analogs or the en.. They are sim­ ilar in appe2n.nce to the TA600, but the faceplate and comrols are slighdy different.

5008 and 500C

With the introduction or FM stereo­ multiplex broadcasting in 1961, the audio world was ripe ror an all-in-onc FM stereo receiver. Fisher, ror their 1962 line, introduced rhe first or the higher powered 5005, the 5008 ($364.50). Peak music power using push-pull 759h was 65 wam (32.5 Wpc). The OUTput tubes were mounted in rront or the OUtpUt transrormers on the 5008. The output transrormers on the 5008 and most other Fisher inregn.t­ cd amplifiers and receivers were made by Todd Electric, Bronx, NewYork.

The 5008 was the first 500 with � built-in multiplex adapter ror rull FM stereo reception. Styling was moderni7.cd wilh the amactive golden-champagne for both mixc:r and oscillator stages, pro­ anodized extruded aluminum faceplate receiver development, using ,he beSt vided a much higher degree of stabiliry, and the gold medallion knobs. Iking an audio engineers available, the culmina­ mechanical noise isolation and a bC:ller FM only unit, the 500B featured a single tion or Fisher FM stereo receivers, the signa! to noise ratio. The FM signal was eye mhe indicator, Golden Cascode 500e ($389.50) was unveiled. 500C amplified by four wide-band IF stages rront-end and four IF stages. There was receivers with serial numbers rrom and converted an audio ignal by a also a sub-channel mul iple filter to 10,000 to 20,000 used the 5008 Golden 10 s t x wide-band one-megacycle ratio detector eliminate background hiss and noise on Cascode FM front-end with a EC97 using twO balanced germ anium diodes. distant FM stereo stations. The rated (6GK5) as the RF amp and a ECC8) The detected audio signal was then red to IHF sensitiviry was.9 miuovolts, separa­ (6AQ8) as the oscillator/mixer. Gone ,he famous Fisher Stereo Beacon, where tion or 35 db, overall rrequency response was the eye IUhe indicator, replaced by a IUning meter and a stereo beacon light. the receiver sensed whether the signal was was 25 to 25,000 cycles with harmonic mono or stereo.

VACUUM TUB E VAL LEY ISSUE #6 GOLDEN ERA F SHER 500

the golden calor of the 500B fa ceplate. The output and power on the 500C are noticeably beefier than those found on the 500B.

The Fisher 800 Series The Fisher 800 (5429.50) was intro­ duced shortly after the TA600 in late

• 1959. It was another FM/AM unit with 1 microvolt of FM sensitivity for 20 dB of quieting. It also featured the exclusive

Golden Cascode fr ont-end identical to the type used on high-cnd Fisher tuners.

AM sensitivity was 10 microvolts with three-way swirchable bandwidth.

The 800 was claimed to be the most powerful stereo receiver of the day. It was the first stereo receiver to use rhe newly , '" "'" I .. - introduced 7591 output beam teuodes .. designed by Westinghouse. Power rating -- I was 80 WattS peak music power and 60 wattS RMS (30 Wpe) with a frequency response of 19 to 32,000 cycles. There , ... , were 20 tubes, [Wo silicon diodes fo r the solid-state power supply and a bridge rec­ tifier for DC on the preamplifie r fila­ ments. The 800 featured 24 knobs and switches for complete Stereo master con­ trol. By the way, the early 5005, 600 and 800 knobs are one-piece and do nOt have the annoying brass medallions that pop off when the glue dries out.

The 800 had a variety of faceplate variations; solid architectural-brass framed fa ce, the solid brass non-framed

face and the thin stamped btass faceplate. There were minor circuit differences as well, performance gradually improved . . , ... The 800 was made from 1959 to late 1961 when it was replaced by the 800B.

In 1961, touted as the very first full multiplex stereo fm receiver, the 800B The stereo beacon used an electronic research needs to be done before any (5434.50) was a beautiful instrument and to eliminate pops from a rclay accurate production figures on popular an outstanding performer. Styling

when switching to multiplex converter. Fisher receivers (an be determined. changed dramatically with a new, cham­ The Stereo multiplex on board wa.� a pagne colored anodi�ed aluminum face­ A 500C is equipped with an incredi­ time-division rype and consisted of two plate, new dial glass, brass medallion ble array of audio controls including: balanced four-diode bridges and a 38 kc knobs and chassis layout. The first dual bass and treble, balance, high filter, synchronous oscillator, which acted as an 10,000 800Bs were made with the 7591 low filter, MPX filrer, tape monitor, electronic switch. Some Fisher enthusi­ output tubes mounted in fr ont of the speaker selector, fu nction/mode selector, astS prefer the sound of the 500B to the output transformers. After that, the OUI­ loudness contour and volume connol. because of the non-NuvistOr fr ont PUt tubes were mounted in their usual SaDe The audio line and phono sections of rhe end. They opinion is that the NuvistOr position, behind the trans�ormers. The 500C used Telefunken 12AX7 smooth circuit is less open sounding. 65 watt OUtpUt section was similar to the plate tubes which were and are the best 500B. 12AX7s ever made. A fo ur-position The SODe is the mosl popular uf the Fisher receivers. Although the Fisher seri­ speaker switch was added to permit the The first 800Bs had three IF stages for al number system is somewhat confus­ use of remOte speaker systems. There the FM section. Sensitivity was improved ing, it is estimated that at least onc hun­ were also jack facilities to use. the Fisher to .9 microvol[S for 20 dB of quieting on dred thousand SODCs were produced. Spacexpander K-lO reverb system. The the FM band and 5 microvolts on the OutpUt transformers were of the highest Serial numbers range from 10,000 to AM band. The AM section also fe atured 70,000. Serial numbers also have a lener quality with gram-ortented and laminated variable bandwidth. Like the 800, the fo llowing them ranging from A to S. For steel cores. The faceplates on 500Cs are a 800B featured separate tuner front-ends example: 34897C or 582195. More lighter shade of (hampagne (Om pared to for the Alvl and FM bands. The 800B

VACUUM TUB E VA L LEY ISSUE .6 GOLDEN ERA F SHE R 500

"IT I'MQMO 500CFM .� tuner 5j!(cificaJionf ,.., ...... , .... ""..."...,., IOW '0" ..... U.. blc Scn,i,i.i,y _.� micro""l..

0) • 70 K(n "U> Sign.al10 No;'c n,'o dB ,'.... ' 8,,� ScI«<;';ly- 60 dB 100 IF "'j«1ionat me - 90dB

Image: RejOCl.on at 100 Mc· 65 dB

FM H.,moni. Di ..onion _ .S�

FM Stne" Sepantion - 35 dB Cap."", Ratio - 2.5 dB

Drir.·O.OI�. SQQCAwVHfiu Sl!cci ficaljOD'

IHF M •. 75 ...ic ro- -nu>

RMS.. ro .,. 66 ....,1$ (33 ""PC) 1000 Humonic OJ.. ,, at eyel..

1"'cnn

-5 0<>45,000 _ rnq... nq _POD..!<' tye]... , aDd 2 dB. and nolsc' 80 Hum dB I>

Chan".] "'p,""uioD• SO dB combines [he beSt of all worlds and is a 1964 and the last all-tube receiver listed highly soughl-aftc:r collector item. in [he 1968 Fisher catalog. The 400 was Tow ",riion •• of bass and ,,,,bl. control, -23 dB. W.... According to AI Pugiiesc:, noted Fisher basically an economy version of the PowerCon,u"'p,;on ao 113 po""'•• 205 expert frOlll SlalCtl Island, New York, Ill<,: 800B it is the most Ilaluable of the Fisher 400 multiplex receillers.

•

�' -.-

The culmination of the dual-band stereo receillers was the BODe ($449.50), introduced in 1964. The BOOe did nOl use NUllisrors (like rhe 5ODC) in the front-end and the am and fm tuner sec­ tions were combined to one tuning . Now there was only one lun­ ing knob for both bands and a different tuning dial glass. Gone were the dual-eye tube tuning indic,lIors which were replaced by a single tuning meter and the STereo beacon ligh t. The filceplate was a lighter shade of champagne. Power and OUtput [f:tnsformers were noticeably Audio controls on the 400 includ­ 400 used the new RCA 7868 NOllar type the sooe 800e. sooe. beefier in both and ed: bass and Heble, balance, loudness outp\JI tubes in push.pull for a GS watt h g filter, speaker t h, music ming. The first 400s used thr« The 400 Receiver compensation, i h swi c tape monitor and volume. There was a IF stages and later versions used four IF Last of the Fisher tube recei"er designs headphone jack on the front panel. A stages. The FM frollt·end was the was [he 400 ($329.50), imroduced in major departure in the output stage, the Golden Syncrode, Nuvisror from-end.

VACUUM TUB E VALLEY I SSU E # 6 • GOLDEN ERA -FISHER 500

VACUUM TUBE VALLEY ISSUE #6 • GOLDEN ERA F SHER 5 0 0

800A Restoration All Fisher rccein:rs are high qUoIlity instruments Ihat should be cared for to preserve their looks and performance. Never plug a newly found re<:eiver into AC until you are sure the fill1:T capacitors in the power supply are formed and that there are no electrical shorts. • • ••• The r«"eiver cha5sis are heOlVY gauge cadmium-pl:uw Steel and are susceptible to corrosion if exposed to moisture when 8008 dusty. I have found several Fisher a receivers with suspicious round or oblong ruSt stains that are rypically caused by a small rodent who relieved irself in the set -- - when in StOrage. It is important (0 dust off the chassis w th a new, soft-paint I I -- i brush occasionally (0 keep moisture attracting dust to a minimum. Be careful ...... around the cha5sis lettering as it will rub offeasily if you use (00 much elbow grease. Dial glasses should not be removed unless you have done this proce­ dure before. They are very easy to break and should be left in place unless you 800c know what you are doing.

If tubes are missing, try to locate the correct ones before beginning restora!ion. The rareSt and most expensive tubes are the 7591A Iype, which are currently our of production, bur are planned to be made by Svedana in 1997 or 1998. Be careful when working around the IF callS, so you do not bend or break them. Slore the receiver in a <:ool-dry area, aw:.J.Y from sunlight if possible.

Early !=isher Ico:ivc:rs used one:-piece: 8008(H) brown plastic comro[ knobs with a gold ring around the edge. Later Fisher prod­ UCtS, starting with the 1961 product line, used a two-p iece: knob with a machined brass medallion on the front of the: knob that is a continual source of problems for enthusiasts restoring Fisher products. The knobs were made in Germany and the glue used to attach the medallion to the knob face: deteriorates with lime and the: medallion pie<:e falls offand get$ lost. AI Pugliese tells nle that he is looking int0 euing the medallions re-manu fac­ turel . Hopefully, these will be available woo.

S uggested Upgrade$ and Modifications

We currently recommend that you do

not convert your Fisher from 7591 A 10 EL34s. The filament current in EL34s Fisher went hack the eye tube tun­ a simpler circuit with fewer switches and 10 will PUt a real suain on the 500C power ing indi or for the 400, insu�ad of the capacilOTS in [he signal path, making for a C:l.l . 6L6GCs are a closer match, meter used in {he 500C. The tuner cb"er sound. 400$ we� sold Allied as by but will result in less power Output and ampli er spc:cificllions were e u co Radio and Lafayene wdl stereo �{ore!; fi q al as as ;11 because they do not have the sensitivity or slightly less than the specifica­ gready red ced prices unlilrhc early J 9705 SOOCS' u of the 759 Is. Also, this modification tions The advantage of the 400 is that il when (he STOcks ran out. . is should be done by a competent te:chni-

VACUUM TUB E VALLEY ISSUE #6

• GOLDEN ERA F SHER 500

Reviving a F..her 500C littl bac g ou � d noise on weaker stereo � k � l . statlons whICh IS apparently IS typical for 8cfor( using fhal old Fi hc 500c (or 400 Or SOO) s r ,ha, you jus, pichd up. here arc somc basic chese units. e.r Steps in , o,ing il. Thi. is ,he b.. e minimum - you .. nn go as for as you wan, I er. Then wo:- checked thc amplifier section of the 500C using a prototype Dynaco 1. Ifi, hasn', be.:n turned on in many ye",s, use e 6oJ8 "i,he, a Vati,,,or ad)usrnblc DC pow r supply 10 CoV-PRO CO player using a tube rn slowly bring ue ,he vol ge on th" fiher apaci,o,.. output stage. Speakers used in rhe vrv Thi. �re-foTm.s ,hem. offices were the Klipsch Chorus I s or B . Weak &W DM110s. At rhe same time, we were 2. Ir possiblr ,e" the ,ubes. tubes will allSe audio dino"ion and weak tuner pe,formance. also comparing a variety of single-ended , amps including ones with 300Bs, EL34s, j. Any obviously burn' f<$iSlOtS or le king ap.ciwrs .hould replaced. cian as it requires atcnsivc rewiring of and sweep tubes. The 500C compared be the cube sockeu and changing the bias favorably to the trendy SE amps!! The SE j. A ",Ienium bridg<',ecrifier(CR_6) supplies power supply. Sn�tlanahas informed us amps had great midrange, but their bass bolh the fi.cd bias for the OUlput tubes .ndD C fiI.­ that they will be introducing their rc­ performance was mediocre and their highs ",elll voh.ge fur the audio pre_amp ,ubes. These almo .. alw.ys d iorar . m.TVing pre-.,,: tubes seemed rolled-off. Some listeno:-rs, howev­ eter � th ':, p issue version of me 7591A in latc 1997 Of and burnIng up ,he prCCJous 7591s . 1he recnfier is er, may prefer this sound charucteristic. 1998. The 7591 is an excellenc hi fi cuhe ,he flu aluminum box on ,he imide edge of the chao­ and is designed for these receivers. To The SOOC had a scamless, balanced sound sis near ,he power ,ran,former (= pho'o on this from top to bottom. It had much deeper pa _ge). If, he old ,ec,ifi., is nOl sho"e�,,,s!licon . modify a recei\'er is to deml.Ct from its b ndge rectifier nn b<: soldered (wllh ,he si l,­ bass and clearer highs rhan the SE 300B across " value, so be patient and carefully restore con b,;dge in the ci,clli,. ,he old rec,ifier is e."'mial­ your receiver while you it for the amp along with good midrange trans­ Iy inert). making sur( the march up ,he _, +, and_ wa ' l leads. Th. silioon b idge will actua ly give tOO much Svetlana 7:59Js to become available. parency. While not a �reference audio r vohage, SO inse l a 4.70. Swan rcStS,or b<:rw«n ,he oomponem, the sooe is an excellent 1000 bridge and ,he flF fiher capaei,o, w give 22 office, '1, choice for your den, second system '·01", ., 117VAC line h.ge. You may wan' '0 or as a stereo television home theater teplac( the dual sec,ion 1000 I'Ff35V apaei,o, (C97 A.m a, ,his axal · p amplifier. All-tube receivers like the ;OOC ,ime wi,h i ty e e!ecrrolyt;a. will never be ro:--manufactured. If someone 4. There are 'wo clectroi)'ties in ,he runerimui1i_ secti . : did, they would probably cost several plex ons ,h ..hould be re placed the 8 �F150V (C-S5) :I ' the ,-a,iude,ec,or nd VIS (10 I'Ff50V thousand dollars to duplicate the quality behi will work fine). and ,he I f'F1250V {C-21O} in the and performance of original models. muhip1ex .ec,;on (a goodl fi m 'YP"works wcll her.).

c ca ac s Colleclabilty S. If you = brown paper oupling p itor in ,he multiplex0' audio I«fion., replaG<: lhcm wi,h When you arc out looking for Fisher ftlm types. The)' look lIke fa, linle ""ran,,,1nndies . it •bau, .75" long. wi,h wi,es coming straigh, out ,he tube receivers, is likely that you will . co ends The)" sound qu;,. bad. Don', nfuse ,hem probably run across a 500C most fre­ with ,he .maller dippedmic> apacitors (wires corn· quently. The nexc mOSt common is the ing OUt One sid() in th( muhiplex """ ion, which are 400 receiver, which were sold at reduced good,and shouldn', be changed. The dear plastidsil­ How do theyPerform? very· 0' white-inside coupling capacj'0r${C-77-C-80) prices by Allied Radio until about 1970. r . c>n be good sounding, bu, may be eplaced Due to the large numb,"r of r",ceivers TA500s, TA 600s and 500Ss are relatively 6. Don', ,epl2cc ,he G<:r:unic cap ..ilors in he RF covered in this article. there is no way wc scarce in good condition and should be t and IF amplir .., m.gos {unlcss acrually brohn}. acquired if found in excellent shape. can givc sonic cvaluations of every unit. Thei, inducuncc and tempe,-a,u(e cocffidenn arc 800Bs are Fisher To give everyone an idea of what a rypical very popular among col­ ma'ched '0 ,he citCUi,. You can repi.ce the ceramic Fisher stereo receiver sounds like, we lectors and currently the mOSt valuable capaci'o,s cI",whe" wi,h film types. ir wan,(d. chose the with a Nuvistor fronc­ Fisher receiver if they are in excellent 500c 7. Don', "Y to .lig.n tI.( FM Or mul,;p\"" sec_ end, which is probably the mOSt common condition. Current 1996 US prices for ,ions unless you ha,·" ,h. righ' equi pme", and know and the overall best sounding according Fisher receivers ranges from free to about wh., you arc doing. Unle.. it is al .re.dy hopdcssly $400+ for an excellelll 800B. The rarest messed-up.• Iigning by ear or IUntng me,er usually to AI Pugliese. I.av.s i, worn: ,han when you Slar

VACUUM TUBE VALLEY ISSUE #6 A T R BUTE T 0 A V E R Y F SHE R

and hean- warming lener." He informed employed as a book designer with Dodd, A Tribute To Avery Fisher me that I had the most extensive and Mead & Company. He would win awards valuable collection of Fisher gear that he for his design work, but not necessarily By AI Pugliese was aware of-a nd I only owned 40 units be credited in the books themselves. In at the time. I immediately framed his fact, it was during his employmem with

photo and letter, which 10 this day hang this company that Mr. Fisher's world over my main stereo console. famous trademark bird was "hatched". As Mr. Fisher himself explained, "Before I went inlO the eleCtronics field, I earned my li\'ing as a book designer with Dodd, I will never forgct my very fim piece: Mead & Company. In creating a design of Fisher equipment. It was a 250·"1: a for their Spring Books Catalogue, I did relatively simple:, low powered solid-stale: the bird, but with a twig in its bill. en receiver, circa 1969. I received it through rOUle to build a nest. When I wem into an inheritance from a rd3tiv(, and with­ the hi·fi business, I simply substituted a Out much thought, placed il on lOp of musical nOte and that is the origin of a TV the family sel and connected a pair of trademark that is now recognized world­ speakers. That was in 1976. It was also wide.n NOI only is this trade-mark world 3tound this lime that J was introduced to renowned. il was synonymous with the my friend and mentor, Mr. Peter ultimale in qualiry and workmanship. Broniecki. He saw the: receiver in my Our working vintage Fisher equipment is home, and immediately wanted 10 buy it. evidence of this. Knowing fUll well that my buddy was an doctronio engin«r, and had a keen Although Av�ry Fisher made his fo r­ recognition of quality, I figured I had tune by designing and building hi-fi COIII­ something real good and should hold on ponents, he was not really an electronics 10 if. When he realized that there was no engin«r. This was not much of a prob­ hope of persuading me [0 surrender this lem, when his usual demand for Out­ receivc:r, he informed me of the: unit's I was �onllnate enough 10 have the standing performance in a unit required high qualiry, value and history. NOticing opportunity 10 com- -�i9:;?"R,J;,::;:_;;pIij;�;;;;:-- my intense imerest in eie<:tronics and municate with Mr. r--=--:--=-____ ------quality recognition, ht began training m.: Fisher several tillles in the field, a process that would contin­ over lhe years. and World of Difference! ue fo r several years. This was the begin­ would often receive --­_- �---.._ ning of my interminable search fo r Fisher interesting bits of --­ ._ ... -- e

VACUUM Tu8 E VA L LEY ISSUE .6

.. A T R BUTE T 0 A V E R Y F SHE R overly sophisticated electronics design work to be performed, he would hire an engineer who would work on a particular circuit ro achieve his specifications. He was, however, almost tomlly responsible for the magnificem architecture, fune­ fiona!it),. and color schemes employed in the high quality Fisher product line. He was, after all, a designer by Hade.

His greal talent for design work was further evidem in the furniture trade as weil. It was during the 1950's TO mid 60's that Fisher Radio produced the finesl quality home high fidelity console sys­ tems ever made. These units, which wefe quite popular in their day, were designed utilizing lOp quali[)f hardwoods and pre­ mium electronic components. They were fine high fidelity music systems as well as classic pieces of qualifY fu rniwre. Custom-made uniTS were nor uncommon, and top-of-the-line models would stretch to six feet or more and tip Ihe scales in excess of 200 pounds. A customer could order one of these consoles equipped wilh means of suppOrt. The U.S. involvement magazine gave the new company a well the finest components available, includ­ in \'(forld War J\ {(·mporarily interrupted deserved boost. Eventually, due mainly to ing broadcast monitor TUners and 130- the business of audio production, with the public's desire for

Throughout his career, AI'ery Fisha never lost sigh! of the importanCe of human needs and customer satisfaction. Never was he inaccessible to any individ­ ual. A common story I enjoy rdating is how Mr. Fisher. upon receiving a gentle­ men who was complaining abOUT his Fisher equipment not working rigbt, sug­ gested that they go to the gentleman's home to have a look. The astounded man brought Mr. Fisher to his house, and in a few minutes, a small wiring g problem was corrected, providing this CUStomer with total satisfaction. Mr. Fisher would often drive to his empty Long Island City pial\[ on a Saturday (they were closed Saturdays), JUSt to answer rhe telephone.

He would tdke a message. promising d return phone call on Monday.

It was this ki nd of genul!le cart: and nEW 0 ... 'l'lfE :\"I·;W F1SIIEH lL\I)]O (·OHl'OH.-\TION I)LAXT concern for his fellow man, that made SI'I'L\'I'E I) 1:-; nn:.\"I'Y -.\I'l(�; FI SI-lE It 1'.\ IU, . :11 J LIlO'. I'I';X:-;SYl'\".-\:-; \.\ Avery Fisher so very special. Never did he

VACUUM TUB E VALLEY ISSUE #6 TUB E L 0 R E A BOO K REVIEW fo rget the public that made him the suc­ 10001)" they are Ijuered with 60 and 70- cess be was, a a victOry so unequivocally story steel and glass skyscrapers. I can Tu be Lore: only imagine how quaint and homey this deserved. Mr. Fisher's productS fai thfully A Reference For Users And served everyone, from the everyday labor­ part of the city must have been when he Collectors by Ludwdl er, to Presidems Tr uman and Kennedy, ran his business hl!re. I can almost see Sibley even tbe King of Siam. In faCt the list of that tin)' StOrefron\, with the words Reviewed by Eric Barbour prontinem individuals who sought OUt �Fisher Radio Corporation· on the glass Fisber equipmem is exhaustive, and was window, tucked neatly in the shadow of a Pllp trb"clt, 8 Ifl If", 519.95 US/S24.95 proudly displayed in the 1963 Fisher typical New York City 1890's brown­ x �/.s�uIJ,m from Ludwtll Siblry, 44E. /If"i'l Sr., Handbook, as well as in other Fisher lit­ none. Fltmilll'oll, NJ 08822 Qr Amiqut El«mmic cmure. Undoubtedly, a list of all satisfied Supply, Tr mp" ArizonA owners of his finely crafted equipment On February 26 of 1994, JUSt ;1 few would be a huge underlaking to compile. days before his 88th birthday, Avery There are quite a few books in print Fisher passed away in New Milford, rdatc:Q to antique radio and tube audio. Surely, it was good fo resighT. noticing the changing trends in business and manufac­ Connecticut. I will never forget how and Many of them are JUSt reprints of old turing, that prompted Mr. Fisher to sell when I heard the news. I had been mak­ texts, and some are in rbe how-tO-make­ his empire to the Emerson Electric ing peTiodic purchases from an old ware­ your-own-tube-amp category. But tube Company in 1969 for $31 million. At house of what [ believe is rhe only surviv­ collecting is one area of vintllge electron­ this time, Mr. Fisher feh it was time to ing stock of vintage Fisher parts and orig­ ics that is nOt well served today. The few 70 give back something to the music world, inal factory documentation known to books availabl�, such as John Stokes' the world from which bc derived his suc­ exist. The building was being sold, and �a1'1 ofVncuum Tubrs alld Va iws and cess. He therefore, in 1973, donated this would probably be one of my last Gerald Ty ne's Sag{l of lbr Va cuum 7i/bt, more than a third of the pre-tax proceeds visits to this historic place. It was a very seem to concentrate mostly on the early from the sale of Fisher Radio to Lincoln cold, sunny Sunday morning. At the very years of tube manuf.tcture. There are two moment that [ stopped my car in front of Center for the Performing ArtS in New books OUl now on Western Electric mbes, York City. this WlIrehouse, I heard the newscaster on so that (small) area is well-co,

VACUUM TUBE VALLEY ISSUE '6 DI T U B E L o R E A B o o K R E V I E W metal, lokr;ll, miniature hunon-hasc, sub­ Priceless information in there--original tubes that produced only ont picturt-­ miniature. lighthouse. button-stem octal, imended application, original imroducing usually standard test patterns, etched on a NuvislOf, Compaclfon, Novar, and even manufacturer (Sylvania in this case), and metal mask buried inside [he tube. Now very obscure Sylvan;a all lhat you know lhe T-9 envelope dale of registration. Try getting where that test figure with the used on Ihe 6GM5 and a few. other types. from old magazines, as we at vrvha\'t war-bonneted Native American came A discussion of lhe early days of V. S. been doing up to Ihis point (or Hying to from. military "high-reliabiliry" es u AKAs and variants, typ leads p do). Even the base IQ the cnd of American production in the pinout, and he;uer data can be difficult 10 There was a mess of nonstandard 19805 thru 1991. The Stokes book does find for some types_ Although nOt all the numbers during this time period, Chapter nOl have most of this information. No lislings are fully detailed, thtre is a wtalth 9 uies to co,'er mOSt of them. tube book 10 dale has any substantial of facts in this chapter and throughout This subjeCl has some gaps, but try find­ coverage of the POSI-WWII industry, so tht book. ing any of it elsewhere. Here are listed Ihis chapter alone should sell TUBE the original developmental numbers of all LORE. BUI this is only the first chapter. the Bendix Red Bank tubes, including some that I have never seen or read about 2 be before Tll be Lore Chapter should read before. The list also includes mOSt special studying the type data. Here are the types by specialty manufucturers: codes for such things as manufacturers EleClrons Inc. (indusuial and and f3 lings, plus definitions of COntrac­ ITT), tions, e rectifiers), Federal Telegraph (later r cch nica l terms and th like. A Heint'L and Kaufmann (uansmining and unique history of the EIA-RMA registra­ industrial), Machlett (exotic high-voltage tion system is here, coverin rhe common g types), Sperry Electronics, Taylor (trans­ I A6-rype desil?nators as well as the earlier radi;a­ 2E26-type This to :J> mitling tubes), ViClOreen (lUheS for deSignations. led the l. tion (industrial W coumers),and We lt{onic later "non-system of the 4-digit series. types). The previous RMA desi nators conrnined filament g such data as or heater Chapler 10 is a re3.)onably complete volta e/ ower, and num­ g p general type or list of military types. The American Army ber of elements. The 4-digit sc:ries starred IJ vr series series and Navy are followed by with 5500 and went through 9019. -- the linle-scc:n Canadian REL types. Chapter 11 co,'en DeForest, which made It shows what a mess the industry Wil:>; n 4-di it series mostly transmitting types compatible wi e of the g are nOt even Chapter 5 shows tht same kind of list a with the RCA 800 series. And Chapter tubes--for e.x nl pl e, the 7223 is a germa­ for the old RCA SOO-series of rransmil­ . 12 is a long, long lisl of Eimac' s prod­ nium The 4-digit numbers ting and power tubes. Cha ter 6 covers r Ucts. It seems that Eimac has been willing were assigned chrono logicalfy, and have the pre-1946 RMA �specia purpose" ro make weird tubes for single CUStoUlers­ absolutely no descriptive meaning for the t'ypes, starting with I B21 and going -their line is full of tiny variations of devices they are attached to. The neXt through 9C31. These were mostly seen in power tubes built on a few basic Stems. chapter is called "PrehislOry". It seems to WWII and were replaced by the 4-digil list all types This list is nOt complete, as Eim"c also attempt 10 the made by near­ scheme. Finally, we plunge into the 4- lllanufuclUrers before RMA makes a mess of customer-special lypes in ly all the reg­ digit listingsin Chapler 7. Ironically, Ihey These the YC series, which are extremely spe· istration began. are alphanumeric start at 5500, a Iype thar apparently never 10 Jists--first a general list, Followed by fami­ exisled. As I said, Ihis list is a real mish­ cialized and difficult get information for ly lisrs each Factory, from Arcturus mash--nlosr arc �industriar types, but about. th o r ugh Van Horne. This was even worse some are intended for consumer use, such All of the big tUbe fac tories had [heir than th e 4-digit numbering, as these as common audio types 6550, 7591, own developmental numbers. Chapler 13 companies cheerfully assigned their own 8417 etc, And you will find everything shows most ofGE's, which are primarily designarions 10 their tubes. Luckily, some from germanium diodes to giant kly­ ind of a (or special things such as photomultipliers, k gentlemen's &ree mcm per­ SUOIlS. Many of the [aler 4-digit numbers haps force of CRTs, vidicollS and industrial Iypes. the RCA S marketing) led to were grabbed by Eimac in the early 1960$ of Chapter 14 is the Rayrheon RK series the 2-digit system being a part of most and attached to their transmitting types, (mosdy RF types), CK (mostly subminia­ these types. With a Few intrnctable excep­ most of which also had perfectly good tube ture), and QK (s iali ed types). RCA's tions, a with a designator containing All the large tube pec z N 5w was probably Eimac designators. 4 a replacement for a manufacturers have been guilty of this 1600, 1800, 2000 and 4000 series are S. T UX-245. Almost as crazy as today's sc:mi­ alphabet soup game. shown in Chapter I he 4000s were conductor industry, eh? the last ones RCA developed before B result Thomson sold the division; it is now is For audio geeks, Chapter will Chapter 4 the alphanumeric list of III boredom, as it lists CRTs from IAP5 called Burle Industries, and still produces M ci l" starting with commer a RMAtypes, through ZI3D4. BUI there are people who m;any 4000-series (primarily vidi­ OA2 and with A rypi rypes ending 117Z6. cal collect rare CRTs, and this will � indis­ cons, Ulicrowave tubes, etc.) entry is looks something like this: p<:nsable to them. Note that this list its sketchy at limes, as manufaCturers often Sylvania had own seri.:s of tub.:s 6AB4 [aka EC92] miniature high-u attached their own numbers to CRT under development, and �hey arc seen RF triode for G-G am s, healer 6.3v p types (and always do today). This chapter (mosl for the first time) in Chapler 16_ @300mA, u 62 (SY) (4-25-49) <5CE>. liSts something mon of you would recog­ The 1200 series was mostly lokrals from Va riant: 6664_ nize the output of, but have never seen the WWll time frame. Later came SA, the actua l device rhat did it: monoscope SO and SN types, most very obscure. tubes were special-purpose camera pickup Like the other special series in this book,

VACUUM TUBE VALLEY ISSUE .6 • THE RANDALL AMPLIF E R

, the Sylvania chapter has some gaps, but Eleclfonia; Newark Electronics, New i or a seeing as Ihis nf m lion is impossible to A Museum Class Inspires an Sensor Corp., Antique Electronic Supply, get any olher way, no onc has a right 10 ele. would be used. And fi nally the <.:omplain. Amplifer amplifier had to round good and, be usable by people who had previously been Ch pler 17 covers most Wcst",rn By John Atwood a using solid-stale equipment, i.e. nOt a Eh.'crric types that are seen in the Magers tweaky, funny-rounding cult amplifier book already. Westin ho se had numer­ u In the fall of 1995, a single ended . ous spe ial series, andg they are in Chapter <.: stneo amplifier was designed for- a muse­ The circuit topology was drawn from 18. I must express admiration for Sibley; r um crafts class, at the re uest of Chris tWO earlier amps: my SEA· I amplifie trying get this corporate proprietary q 10 Boencher. Chris, a member of our Bay using three 2A3s (described in 501md information, about obrolete products Area Tube Enthusiasts group, works at Practim-Fall 1994), and John Broskie's made by now-defuna divisions, must the Randall Junior Museum in San dual-EL34 single ended amp. John have required the patience of a saint. - Francisco as a curator of industrial art), Btoskie's amp pro ed that twO triode-con­ nected EL34s drivingv a Onc Electron A ood book could be derived simply The museum gives artS and crafts course g 1.6K Output transformer could fronl Chapter 19. It's called a Uscr for children and adults. Since woodwork­ UBT-I sound quile good. A key to his design GuideM, and gives information� on tesling ing is his specialry, Chris has taught class­ rejuvenating and fixing bad bases on used, es in guitar building and speaker build­ was the connection of of grid #3 (sup­ pressor grid) to the plate, instea of the or damaged tubes. This chapter actually ing. After he gOt interested in tube amps, d cathode as is usuallv done. Tht driver describes dare coding on most American he asked me if I could teach a class on brands--try finding ,hat in your old text­ tube amplifier construction. Ha"ing circuit of tht Rand;ll amp was a somt­ books or tube manuals! recently built some single-ended amps, what down-sited version of what ,vas in and being in the process of putTing Ihe SEA- I amplifier, using more obtain­ The firsl lengthy discussion of TV together the One Electron transformer able tubes. The power supply is based on sweep tubes in publishing history occu­ product line, I thought that a moderate­ the One Electron BFT- I power trans­ pies Chapter 20. Nearly all the <.:ommOI1 power single-ended amplifier would make former, which was developed 10 support American types arc listed, along with typ­ a good projecT. Since that time, tWO class­ the Randall amplifier, as well as olher ical e uipment other than TV sets that q es have been taught and the �Randall stereo amplifiers in the similar power used th em . Some unusual hi-fi and guitar A.mplifier� that resulted is now on the range. amps used sweep tubes, along with a wide market. The design philosophy, devdop­ variety of ham-radio and CB linear RF It was clear that a CU�lOm chassi� mem, and class experiences will be cov­ amplifie . Sweep tubes occupy a lost would be needed make the Randall rs ered in this article, 10 world, and Siblcy has done it a prieeleu amplifier attractive, rugged, and reliable. favor by documenting il. for The chassis layout is reminscent of a Design a Museum Dyna Slereo 70_ An interesting variation, Chapter 21 is a lengthy list of recent Since rhe class al rhe Randall Mu)eulll though, is the use of a sub-chassis to sup· auction prices for various tubes, compile d would be open 10 anyone, the amplifier poT! the OUtput tubes and re<.:tifiers. This from auction rcpons in magazines such as would have to inexpensive, simple to was originally done to pre,'ent the inser­ ARC. As Illight be cxpe<.:ted, it's not very build, be easy to use, and be Kbullet_ tion of metal 6L6s or 6550s - [heir pin <.:Omplctc and <.:Ontains mostly I're-1930 proof." I also wanted the amp to be a Is are a!lached to their melal shells, while radio t pes. Neverdleless, it gives some y statemem of tube technology, which in the Randall amp, pin I is tied to the idea of values for ea l types. Because this r y meant no compromi.5CS with rolid·state plate_ By physically preventing tht inser­ market is unstable, we probably will not components. Simplici[}' of design and tion of these tubes, a safety problem is sec a convention l pri<.:e guide for tubes a COSt considerations led to an integrated averted. The sub chassis has other bene­ for many ears to cOlli e. Besides, most of ,r stereo amplifier. I knew from work on fits: it stiffens the chassis and provides the "junk TV !Ubes you at flea mar­ see modifying conventional stereo tube amp) shielding between the power supply and kets arc and probably always will be that i( care taken in component loca· the input circuits. The main chassis is worthless. But the hardball colleclOrs gO was ti n and power-supply filtering, virtually made from 14 gauge steel. This is thicker for Ihings like the single.wing o the same performance could be achieved r ll ($1400) and the Qscillion ($2100). And than usual, bUI results in a ea y stiff, as having two audio triodes, such as 50 and single-plate Kmonoblock� amps. 2A3, are quick-cash thin s to be shipped ! Adding an input to the Far East. Finally, tl ere is a I-page level control and index at the cnd, with keyword listings. making the amp rel­ This book is nOt perfectly exhaustive. atively sensilive

No hook is Yel Sibley has done an allowed it 10 be run impressive job, of gathering information directly from a tuner that no one has dared to collect in one or CD player with­ place before. The post-1945 data are out a separate pre­ regarded br the :lmique-radio crowd as amp. To keep the borin� an{ un important, yet any de<.:elll amp inexpensive and histoncal lexl on tube clectronia; should maintainable, only co,'er that era. Anyone with the nerve 10 pans that are readily cal! themselves "!Ube cxperts� should own oblainable from TUBE LORE_ It is one of the mOSt sources such as Digi­ mandatory books in this area, Key, Mouser

VACUUM TUBE VALLEY ISSUE .6 • THE R A N D A L L AMPLIFIER solid chassis. Anyone using a tube amp!i- fief has already foregone lightness and efficiency, so we might as well go all rhe way. Besides, steel is cheap. A grey-wrin­ kle powder coal finish is used. This is remarkably like the classic solvent-based wrinkle finishes, bUI is very rugged and environmentally-friendly. Drawings were made up, and the chassis were built by a local sheet-metal shop, U.S. Fabrications, in San Jose, California.

A circuit board had been considert:d, bur in the incerests of COSt and period amhemiciry, it was decided to go wiTh point-to-point wiring. This made the construction phase more difficult, but made ci rcuit changes and parts substitu­ Tion a lOt easier. A set of wiring diagrams was produced that showed the sequence of wiring and pans installation.

Circuit Details and 16 ohm OUtputs. The maximum allows use on power line voltages from The ft-lndall Ampjifi<:r is a conven­ power is about 13 watts per channel 100V to 240V, 50 or 60Hz. Note that on tional single-ended amplifier using all before dipping. A small amount ( 3db ) .he fo llowing circuit description, rhat medium-mu Hiode amplification. The of negarive fe edback is used IQ increast where the schenwtic diagram reference UBT-I output transformer provides 4, 8, the speaker damping factor and reduce designators have a dash C -") in them, the distortion. The BFT-1 power transformer part is used in both channels.

The first stage is a triode-connected 6Sj7 biased :It 3 mA. This has a mu of

20, making it similar 10 a 6J5 or 112 a 6SN7GT. The. second stage uses a 6SN7GT with bOth sections parallel<:d, biased at 11 mA. Thc small cathode capaciIQr (C-05) is used IQ booS( tbe OUt­ put at high frequencies to compensate for the capacitive loading of the output stage. This technique, called �cathode compen­ sation" was originally developed for use with amplifiers.

The output stage uses tWO triude-con­ n<:cted EL34s, biased at about 125 mA. An unusual aspect of rhis stage is the con­ nection of the to the plate

__ . through I K parasitic suppressor . k"'_ ... .. ___. ... _. � ...-- ... - .. , ."'... .. Experiments done by John Broskie and -- ...... _-_._- .,.. . , - ... _ - ._- "", , - others showed this to be a better sound­ ing configuration than if the suppressor is connected IQ the cathode. Cnhode bias is used, which is stable enough to not require any adjustable bias controls. Th<: positive cathode voltage, about 33 volts, is connected to the twO heater windings. The elevated heaters help reduce hum noise in the driver stages. An OUtput • and ..• . " stabiliz.ation network (R-19 and CII) is " needed to avoid oscillation with cenain inductive speaker loads.

The power supply is a conventional capacitor-input vacuum-tube rectified supply. It was originally designed for twO 5V4G rectifiers, with the hope that the inex ensive Sovtek �5V4G�s could be. ,.. '.1. 'IW". I""" ..,,, ..... p The Randall Amplifier used. [t turns om that these have a much

VACUUM TUBE VALLEY ISSUE #6 THE RANDALL A M P L F E R

low�r current rating than real American film or metal oxide. All coupling capaci­ SV4Gs (less than 125 mA vs 175 mAl, tors are �Xicon" polypropylene eypes, as and problems with arcing occurred. arc: capacitors th3t bypass all dectrolyrics. N.O.S. 5V4GAs worked well, as wdl as Small capacitors are either mica or poly­ Chinese SAR4s, which are used in the styrene. The critical output cathode current models. RI, a 15 ohm , bypass capacitor is a P3nasonic HFS low­ limits the peak charging currenr. both ESR type. The B� filter capacitors seen protecting the rectifiers, and lowering th� by the amplifying stages are the British overall sysrcm noise. R2 and R3 arc: LCR type. The filter choke is by Stancor bleeder resislOrs that also equalize the (although made in Thailand), and the voltage across rhe: input filler capacitors. transformers are Onc Electron types. The tube sockets are mil-spec Russian ceramic Special care was taken with the: high eypes. Although these: partS make a good­ volTage dislribUlion and filtering. None sounding amp, some students substituted of the: amplifying stages share a common even higher qualiey pans (see sidebar). filter capacitor, reducing interactiOn to near mono-block levels. Ofu:n, single­ Class Dynamics ended output stages dislUrb the power Before applying power, I did a visual Ten evening sessio!l�, on.: a week, supply enough to cause "11lolOrboaring" check of {he wiring, {hen ohmed-o\lt crit­ were scheduled ror the class. The first twO or other kinds of feedback. The driver ical circuitS. Power was applied in St3 eS, classes were lectures on the history of !? stages are filtered scparau:ly from the out� and once we gOt past the "smoke test tube amplification and basic theory. The put stage to reduce interaction between phase, the amp was tested for frequency next six classes or so were dedicat these Stages. A is used in series with ed 10 response and distortion on a Sound construction, and during the last tWO the filter choke to ,he output stage to Te chnology 1700B distortion anal)"er, classcs, ,he ",mps wen" checked and test­ protect [he outpUt transformer in case of Te ktronix 561A oscilloscope, and ed. The class si�e was limited to ren. Two a tube short. Heathkl IG-127S function generator. At classes have en given the first at i be so far, this point, some subtle wiring errors were Despite rhe stagl:S of fil".. cring to the end of 1995, and the second during tWO of en fo und. Once the wiring was co[­ spring ! 996. About half of t'ach class t the output stage, 120H� hum coming recled, all lhc amps came OUI with sur­ from the B+ supply was present in the prisingly consisre!H performance: about Output of the original design. Raising the 13 watts rms per channel before clipping, filter capacitor values would endanger the about 2 to 3% THO at 5 wattS output. tube rectifiers, and there was not enough room to increase the choke si�e. A form Resulu of hum Cllncdlation was used 10 reduce Students who had only used solid­ the hum substantially. By tapping the B� Slate ipm nt loved the sound of tht supply to the first sta e from pa t way equ e g r between the raw +444 volt supply and Randall Amp. (This is kind of like shoot­ the wdl-filtered supply to the second ing fish in a barrel!) Some of the swden(5 stage, enough 120Hz signal from the r.lw were dedicated high-end audiophiles, supply is fed into the first stage IQ cancel were people who had had some tube elec­ familiar with the beST push-pull and sin­ mOSt of the hum fro m the output stage. tronics background, bur rhe rest had little gle-ended tube designs. They fo und the The correct ratio ofR-8 IQ R-17 was or no electronics experience. Most Stu­ Randall amp the be very competitive, found by substituting a rheostat for these dents came from San Francisco, but a few especially after using high-quality compo· tWO resistors, and adjusting it for mini­ (including the teacher!) came from as far nents (sce side-bar). One studelll report­ mum hum. If changes are made to the away as San Jose and Santa Rosa. The ed the amp sounded better than $5,000 stage gains or filtercapacitor values, these Randall Museum provided workbench single-ended amps he had heard. Most resistors will need re-adjustment. space in their woodshop, as well as sol· fo und that the power level suited their deting irons, solder. and handtools. In speakers. Speakers used ranged from no­

The grounding scheme is a fo rm of addition 10 :.l S72 tuition fee, each Stu­ name department store spe",kers to �hierarchical STar grounding�, and is dent pai d aboul $475 for the partS. This Vanderstccns to LO,",1:hers in custOm-built shown in the schematic. The grounds for pans price is only minimally marked-up cabinets. The most serious power mis­ each stage is starred at a single point, over cost. match I found was with my own then these stars are connected 10 the next Celc:stion SL-700s - JUSt toO inefficient. lower-level stage's Star. The grounding On the whole, the classes w�rc quit� between the tWO channels meet at the successful, with all but three pcople fin­ Aside from compOnent substitutions, power supply, and are connected to the ishing finishing their amps during the some of the students made some modifi­ chassis near the input connectors. An scheduled classes. Two 0 those three have cations to suit their sonic tastes. Several important part of this scheme is that the since finished the amps on their own. e);perimented with removing the feed­ output common lead is grounded There was a definite spre",d in construc· back. The general conscnsus was that through the feedback shielded to the tion quality and wiring skill. Some people with no feedback, the sound was more input stage's star ground. This grounding quickly and accurately wired up their dynamic, but that complex music could amps, while others took time and needed $Chen�e works well, with very little hum get congested. One student added a or nOISC. help in getting the wiring right. switch 10 bypass the first driver stage Interestingly, people who had no prn'iou� (thus also eliminating the feedback and High-quality yet inexpensive compo­ electronics background often did the reducing sc:nsitiviry), finding that elimi­ nents arc used in the Randall Amplifier. most accurate wiring. nating one stage helped the detail. One The plate or cathode resislOrs are metal

VACUUM TUB E VALLEY ISSUE #6 THE L 0 F T N W H T E A M P L F E R

Randall Amplifier SwdeElt Listening S. Yo ung White was born in New Impressions Using Designcr The Story of the Loftin­ York City in 1901 and worked at various Components jobs including shipboard radio operator White Amplifier and in the General Electric Company �r:tl lludwta experimented with pu((ing Te st Depanmtnt. In 1924 he joined the high-cnd "doi gncr" romponcnu into their By Alan Douglas Loftin-White Laboratory. After the .mps. He« is wh •• SOme of them found; Second World War he surfaced in New Geargt' K. a(lC,imcn.cd with pUlling bolh H""land Musicaps and old mil->p« pap'" Yo rk City in the ultrasonics field, writing a lengthy series of articles for AUDiO capaci,ol$ in '�coupling capacitor positions. Conventional audio hool wisdom He found .he be.. combi... ..ion wu ,he stock p maga:tine in 1947-1949 on high-sound­ has it that direct coupling, when it Xiron cap;!cllon for .he .22 ..F and the le:\·d experiments. His credo seemed to appeared in 1929, was far better than Mwiap$ for .he .47 ..F position•. �If I can't hear it, harmless� but anythin else in existence:, was a be: it's Chant; S. and Mike B. did a.cnsive tinen­ (; one wonders what became of him. resoundIng success, and lives today in ing .cns with m.oy compon.nta. They uStd Incidentally, in the August through Cen_Fine ekclfolytics in place of theLCR audio systems worldwide, a te51arneru d capacitors and cxpe.;men.ed wid, ",mov ing ,h. December 1948 issues he showe how to to the genius of its creators Edward H. make your . film byp"s.JU .round them. They found a los.! Loftin and S. Yo ung White. own of dc.ai!' SO pU! ,hem back. Nichicon "FX" c>paci!<}fI for ,he 2200 hod. An Engineering Team WUt Ulffl 1'1', •• Evtry of thae if wrOllg. bYP"lses. Many .cm wc« don. on ,h. CQupling I)flr foers c'paci.ors. Audio No.e paper and oil (alu­ Loftin and White joined forces in Direct coupling fifteen years old minum fo il) wcr. r,,,, "10 be on a method of stabilizing the: grid bias in evcrywhtt(;. Film byp","" of big tlce:­ invent? Why did the recognition they used ,ht direct-coupled amplifiers, an interesting lrolytH:s we", impo.<2J1I. craved, arrive sixty years tOO late? laboratory exercise but of no commercial In the Beginning ,·a lue. It did, however, indicate the direc­ person fo und th:l.t when driving his JBL tion their work was raking. By mid-I929 Edward H. Loftin was born in speakers, the bass seemed too loose. I they had solved a technical problem that Momgomery, Alabama in 1885. After modified the fe edback from 3db [0 6db, previously had prevemed the use of the graduating from the U.S. Nav:.ll Academy and this satisfied his speakers. 50 tube in resistance-coupled amplifiers. in 1908 he held various high-level posi­ They presented another IRE paper in Due to popular demand in the South tions in Naval radio, before resigning in November 1929 (published in April Francisco Bay area and around Santa 1924 to take up private research and 10 San ! 930) and attempted to license their new Cru7., I will likely give courses in these act as a patent atlOrney and an expert in rnedlOd to radio manufacturers. The patent suits. By successfully prosecuting areas, as well as probably more courses at January 1930 issue of Radio News pub­ the Randall Museum in San Francisco in fifty of B. F. Meissner's patent applications lished some hints of the new develop- the fu ture. I have also made semi-kits and on AC-powered , and licensing var­ fully-constructed amplifiers available ious radio companies before finally selling commercially (see the One Electron ad these 10 RCA, Loftin received Illore than on page 35). This class has been a good $300,000 in royalties up to July 1930, which money doubtless financed [he proving ground to see how a design can be built by everyday people and how it Loftin-White Laboratory. But he � will work in real-life situations. It has also gOI into marital and stock­ really been gratifying to help both novices market difficulTies, and and experienced people get into tube was soon down and out, dectronics. according to Meissner's autobiographical F", m"" infimnllti"n "n tIN RA/uIaH account in "The Early Museum and its aC'tiuiria, write: TIN !VU/dalJ History of Radio Museum. 199 Museum Wa} San Frdndsc". GuidanceB (San CA 94114 USA, ", I40Ir at Francisco Press, http://www.W(,,.(oml�tlaMrantlail.hrm1. 1964), and report­ edly died alone in F", information on the &ntla1iAmplifier, a New Jersey (Ontau: Onc Elearon, 65 Wa shington SI., trailer park. #137, Silntll Ciai'll, CA 95050 USA, o,loolr Ilt http://www.onr-eiectron.com.

VACUUM TUB E VALLEY ISSUE #6 T H E L o F TIN w H T E A M p L F E R

menl, and beginning with February a touchy hum-buckin arrangement that g lengthy series of anicJes containing the fed an out-of-phase hum signal back 10 ma azines jumped details. Several other g the 24 cathode. But largely, hum with on the bandwagon, and thus were the: dealt with by ignoring it, on the reason­ - names of loflin and While indelibly abl.:: assumption that a small speaker in associated with direct coupling. an average radio would not respond to 60 Hz anyway, nor would the output trans­ Why Direct Coupling? former pass it. It is necessary backtrack, under­ 10 (0 Hen.', then, was wh3t Loftin and nand what Loftin and White did, and White presented to the world: a rather why. The 50 tulx:, developed by clever box of tricks that allowed a small Westinghouse for RCA in 1926-1928, radio to use a high-power SO tu�. This -f@ the largest practical OUtpUt tube for WlU filled a n�d and mi ht have i>«"n a mod­ home radios, used wherever morc than g .::sI success, had not ("a te (read "RCA�) L- L_-I _ the 2 available from 71As was need­ w.ms intervened with a better solution: a new .... ed. But the 50 was prone to grid emission tu�. ' " . " , :olnd gas, so the maximum grid-circuit " ,r resistance waslimitcd ohms. � 10 lQ,OOO RCA's answo:>r 10 the audio-power '. Now to gel reasonable bass response from dilemma was the 45 tube, not toO small � a resistance-coupled circuil, a large cou­ (71A) , nOt toO large (50), but JUSt right. � pling capacitance was needed, and this Usable on a low plate voltage, well within - created twO problems. Available capaci­ the capability of the full-wave 80 r.::ctifier • tors of that size tended to be le:.a.ky, and and practical ele<:lfolytics, twO 45s in momentary overloads charged up this push-pull could produce enough audio large C:.I.racitor and blocked or Cut offth.: volume for any re:.lSonabl.:: radio set. RCA 50 unti the charge leaked off through the imroduced the 45 in March 1929 and it grid resistOr. A lower grid resistor helped immediately superseded the 71A and SO; exploit (h.:: owned a resistor-manufaCtur­ the latrer problem but re

VACUUM TUB E VALLEY ISSUE #6 • THE L 0 F T N W H T E A M P L F E R

1929, or some might have been brought expanded on his theme in a book High ladies who, whcn asked whcre they back by a Kinsuido agent. Incidentally, Fidelity Radio (Bernards, 1952) but bought their spring hats, snipped �\'(/e Tokyo Elecuic combined in 1939 wirh app:.uenrly had little further influence. HAVE our hats".) After all, there has to

Shiba-Ura Engineering Works \0 form be a reason for hoarding all lhis junk for IOday's Toshiba. Modern Loftin-White Applications thirty years, yes? [n the March 1961 Popular In June 1935 the LUX661A appeared. Ideally, I thought to myself, J should Electronics Herben I. Keroes, co-invcntor using the original Loftin-White circuit use 5ilver-Marshall pans since they were of the ultra-linear circuit, published plans except that a 57 replaced the considered the best obtainable at that for a �Loftin-White" with 6BQ5s. Not obsolete 24. So while the Loftin-White time, and were widely sold by mail ordtr. surprisingly it used transform ers and a was forgonen elsewhere, it was alive and But evidently I wasn't going to cannibal­ printed-circuit board madr by Acro well in Japan. More consuuction plans i;:e a good piece of equipment to get Pruducts, Keroes' company. appeared soon aftef the war in one elec­ some, so ! began searching the junk in Uncharacteristically for modtrn '"Loftin­ tronics magazine, and fr om time to time the shed until 1 found a derelict power White" designs, Keroes did use one of the during the 1950s and 1960s. Direct cou­ rransformer and filter capacitors still bias-stabili;:atiol1 schemes proposed in pling appears to have been re-introduced attached to a bi[ of sheet iron. A quick 1929, referencing the input 12AX7 grid to the Western audiophile community uia! revealed [WO 7.5-volt windings, per­ bias to the GBQ5 cathode current. Somt from Japan when Jean Hiraga published fect for my amplifier, and rven a 2.5-volt less-informtd modern constructors have "Le Circuit de Loftin et White" in issue for the 24 tube. This was too good to be copied the original circuit (eXCept for the no. I of L'AlIdiophilt in October 1977. true, especially when cleanin off the rust power supply!), even to the hum-bucking g and dirt left a very resentable specimen, capacitOr. However, well-designed direct­ p Western Remnants of the Circuit bur then on a hunch J went through coupled amplifiers hardly resemble the some Silver-Marshall literature and found Yet Loftin and White had not been original Loftin-White circuit at all. eIHirely fo rgonen in the WeST. this exact item: the sheet iron had been Stromberg-Carlson built a commercial Modern direct-coupled amplifiers can the interior partition of a 1928 Silver­ amplifier in 1953-54, the AP54-LW with sound very good indeed, but what of rhe Marshall power pack. So the filter capaci­ four push-pull direct-coupled stages original Loftin-White? Many authors, tors were also authentic! They proved toO (I2AX7-l2AX7-6AS7-pp 81 IAs) and among them Keroes in 1959, have leaky to be trusted in actual use, so my there was also an APIQO with fo ur claimed that it was better than previous major concession to modernity was to 811As. Lack of any bias stabilization designs, but we should remember that hide Mylar capacitors inside the old cans. probably explains why it became the Loftin and Whire's own words were It didn't maner if the low-voltage AP54-CC (capacitor coupled) in 1955. "smallest and cheapest." The way to find bypasses leaked, so I chose rn'O lo be out was to build one. Duplicating the Deutschmann units imponed from In July 1948, British pipe-organ original circuit is easy enough, but J Germany in 1925. Tobe was a colorful authority Rev. Noel A. Bonavia-Hunt decided also to recreate the original character whose brother Arnold founded published a circuit in Wireless World for appearnnce with authentic pans, an Radio Shack. He also imported excellent a 20-wan direct-coupled amplifier (he did instant "collectors item" if you will, sinc", f glass-scaled resistOrs, some of which I not use the term Lo tin-White) using no original exam les appear have sur­ p 10 found, a real stroke of luck since good parallel DA30 triodes. He claimed great vived. And I needed something to illus­ units of the right values that will with­ sonic benefits fr om direct coupling but trate this article! did not seem bothered by the 8 mfd elec­ stand hundreds ofvolts without changing trolytic coupling rhe DA30s to the OUt­ Building the Loftin-White Today resistance are scarce. Molded carbon resis­ put transformer. His circuit drew a fusil­ tors had bardy been developed in 1930, While several of Loftin and Whito;:'s lade from such readers as Peter Baxandall and [ eventually had to use one made a br�adboard models were pictured in do sincerely believe it desirable to do couple of years later fur the 25k cathode Cl Radio News (some actually built on what one can to stop people building resistor on the 24. Finding the 5k wire­ wooden boards as was common practice amplifiers of this kind"), Bonavia-HUIl1 wound by Elcctrad was another stroke of of the day) luck, as it was unused, wirh its protective .. � there was no cardboard sleeve, though [ had to "bor­ r;; .., ------�_:_:::�_:::�� ��------, "definitive" row" some slider raps from other example IQ Elecuads. The stamped Bakelite strip copy of the 24- with input and OUtpUt jacks came JUSt as 50-SI version, you see it (why would anyone save junk the one I wam­ like this?) and cven the oak board, com­ ed to build. plete with holes that I hid by careful pans

And [ wanted arrangement, was a bit of office furnirure to limit myself Illy father brought home from the insur­ to pans J ance company in 1945 (it runs in the already had on family) . hand, partly to save time and The output transformer is a story in effort, partly as itself. Finding one that will handle a 50 is a maHcr of no joke, and I wasn't about 10 dismantle l��;@��I��honor (recall my 1928 Zenith console. Besides, [want­ {he proper ed a Silva-Marshall, to give Loftin and Bostonian White the benefit of the doubt on quality (bur note that the outpUt transformer was

VACUUM TUB E VALLEY ISSUE #6 la THE LOFTIN W H T E A M P L F E R

underfillerc:d half-wa,·c Hunt's book, whil� Russ Hudon fo und supply is atrocious. It Ihe Stromberg-Carison schemarics. measures 26 dB down, or 5%, IOlerable: on Particular thanks to tWO correspon­ 1930 speakers but all dents: Desmond Thackeray pointed OUl that Loftin and \'\I'hite cam� close 10 (00 annoying on mod­ ern ones. Especially inventing bootstrapping, long before any­ when using the Silver­ one else, and could have applied it to MarshaIJ �Unichoke� as increase rhe apparenr impedance of the: an OUtplU transformer, grid-return resistor. But they abandoned with itS good bass it without ever realizing what they had, response:: down &lB al by bypassing (he ;0 cathode to B-plus. 40 Hz and 6 kHz. The Nobu K. Shishido (Shishido Koichi) SiJver-Marshall 221 has also built a modern replica of Loftin OWpUI is 6 dB down at and White' s original circuit, with much 80 Hz and 11 kHz. 1 the same result: decent performance bUI kHz harmonic distOr­ intolerable hum. His findings, and a lion with the Unichoke descriprion of the Loftin-White brought i56%al Wimo 10 I up to present-day audiophile standards, ohms. With the 221 it ar� in MJ magazin� for February 1996. is 8% into 1000 ohms, Shishido-san obtained the Lux hislOrical mosdy second harmon­ information from the present-day ic, 1.3 % third. These: Luxman firm, as well as other material on figures would improve the poSt-...ar Japanese audio scene. at a higher B-plus and , by re-biasing the tubes, but rhe hum won't go away_ Even adding another 22 mfd of fil­ Bibliography tering (no clectrolytics, ..... 1916 remember, al 500-plus Rodio N Nuv. PI' )04 W6. �8S Oy.!. fltcb S''''''Y.roupl.d filCh ...,n 'h" .. "".,"'" .bove. I volts) the hum is audi­ .ire";,.. rn( or. 'oo laky(Of ,esi".t>«-. 286 ble, and this is with a !'roe.I.R.E. �htch 1928 pt>. 281· \...oh,n &: "-';10.,,,, real 3D-Henry choke ffioo\iu, ...to; ... .. in dir«.� ....plr ..... (bu�.P-" . (measured al the 37 •m! ,ub.. only). RaJio 19� pp. 600·601 loftin Wh". MA New. J.". &: considered �part of the speaker" and nOt operating current). Much of the $o:h.cm "' ''''" ..i<. ;' ' PO'" ,...]""". included in the published frequency­ residual hum is from the directly- Rod;" Nnoo l'cb. L9� pp. 704·70�. 76J·7(i� Loftio rcsponse curves, a ncat bit of chicanery). heated 50. &: Whi.e Circui. do... Rod;., Wo, ) In the barn I recalled seeing a Silver­ ld Fd:>. 1. 1930 pp. 1·13 . E. And.f"'" . .. \d What ki lled the Loflin-White? Later If«hnicol .difOf) Som ,\;« (191 Sl. Marshal! whalsis, that on inspection H.nky. Mo,p-" (1919l.John. .,," (1928). Pul. ( 1925). writers claimed it was 100 tricky to proved to be a dual choke with high- and Radio News M.«h 1930 pp. 801·802.873-874 loft... low-resiuance windings. Intended fo r a adjust, no snap even with Te kuonix &: %t." Circui<. l.R. E. Ar,il 1930 pp. 669·682 The same can be said of modern direct­ loft," a:Wh". Silver-Marshall output transformer, also ,11< ","" ".at cite"i, .nd okvdopmcn' p'''""'" coupled designs too: they eliminate one ...... from the 1928-1930 period, that matcho Rodio N Moy 1930 pp.JOO.l·IOOS. IO�·IOSS .... ""'... iD...... 1000 ohms, the impedance of a Wes tern coupling capacitor, but still contain r o \...oh," a: Whi« Muallo_ ,..... of [kc,ncI,Ampl<>.. tu.) ..... Electric 540AW cone speaker, one of the or mor� bypassed resistors which are JUSt modcb. Radio CroftM.y 19W pp. S84·�86 Sui<: p"""'pko, best available for home use then. as surely in the signal path, along with ...... Rodi N J"I>< 1930 pp. 1 10-1-1 10S. 1146-1147 tht' power supply. We ....on·1 even mention <;,,,,i•• Performance of the two output devicd is Loio,n a:Witi", At> uobWo«d pwh.p...u ",d ...... ,m... • comparable, as we shall see the OUtpUt transformer, except to marvel win, :IO-_n ,,,be 00 12)OV...... ju ... al how tube fans can make a virtue out of Rodio N. 1930 pp. 111�1116, 11�7 G..,,5" FIe",in! (Loftin.Whi« L:obo... oryl Hi>,0'Y' including Auditioning the loftin-While necessity. Now that the fu ndamental E. pa'""' 1,112.655 "fG.W Pi.,... iu ....JOcr. 6. 1914 and rationale fo r direct coupling-coping with 1.129.9-'3 ofH.D. Arnold. fikd M.. ,h 28. 1914, iswcd So who do we believe, Loftin and M""h the flawed 50 tube-is gone, the words 2. 1915. White or the modern writers? You Radio Cnh . MOl< I>o.oa.; �poilltlcss exercise� come to mind again. Jwt.< 1930 pp 64(0.647. 661 .. guessed il, �smallcst and cheapest" wins Rad", En"n ,i.a Jun. 1930 pp. 63·6-1 O,i"n.1 ci,· hands down. It sounds ri ht, if you '"It all g A number or friends have contributed .... jy>t

VACUUM TUBE VALLEY ISSUE .6 • THE pow E R K N G S 6 5 5 0 AND K T 8 8

Rad;" �. S-227. 281·�82 G The Power Kings: 6550 (P""""" 0(Cmndio, ...pplic. of,he raDtorS op«i focd) KT88 On&,,w CJ""", bo". ""'"""� nJ.... and Radio Now. .• Oa ,}O pp. 322·323, 383 Cco.thow•• "mplifK0 bi.. on ,hr 24. important, or that average bass-reflex &0. LM. Bate'" Rodi" CrohAU8' 1?33 pp. 81. 111 speakers will give plenty of loudness with 1.0<. of 0'''0'1) Iw:,'o' 1. History ci""," (HenI><)' 1933) bu, I.W .. II add«l fo, bi ... Rodio er.f, Mar. 1'137 pp. S.H.SS7 Ap,il 1937 pp. In the halcyon days of hi-fi, swing 1 6Ol, 622 July 937 pp .l-6.62. A. C. Shan.,. (Amplif,er Co more than 30 waItS was relatively expen­ Ammn) Dir«'--..p&c.I puoJ,.pull 616 pli er. 01 :un f, U.... sive. h rC" '0 beunb.l .nc..!. Rod;"1'01 . ... AuJ. 1937, pp. 89. I�I. G.J. Kdl.y typical 300-400v plate voltages. or trans­ l\uh·pull 2A30 . Of W.. POO' ...... mitting tubes at much higher voltagC$. 91. AU>".d Rod;" "ul-CnJ. 1937 pp. 124 ....a«ull Even though a pair of 8075 would do the ..... •2A6 lAJ. V..,.. .",pi<. job, the plate voltage would have to be Rod;., N...... 0..:. 1937 pp. 336-337. 38l_l-83 T,oodo:­ upJcd ... ou'pu' fr.ndi>...... more than 550--this usually required oil Rod;"Au CnJ. .. 1939 pp. 16-18. S7·S9 A.c. SIwrq capac:;itors in the power supply, plus mOro: 1\uh·1'I>11 bur Lw nop/w< .i"<1, ""I...... lllpu' ,ruu' expensive transformers that wo:re rated for m.rn<'. such operation. The price added up, and Rod... CnJ.Qc,. 1939 pp. 202-203. 2.H·23S A. C. !Nn< .rrKt..-couplod l ...,..k. transmitting-tube power amp. p i, indud< any ,m,. There W3.5 unquc:5tionably a Slrong l 1riodco in of>< .ngl"or

VACUUM TUBE VALLEY ISSUE #6 THE pow E R K N G S 6 S 5 0 AND K T 8 8

allained in mOST existing designs by rhe use of fo ur or more tubes." Th anks to the large low-loss base with molded-in dams between the pins, to discourage leakage currentS, the 6550 was rared for 600 volts on rhe plate and 400 volrs on the screen. It had about twice rhe transconductanCe of the 6L6 types, so it could produce 100 wattS with about the same drive volrages as Ihe 6L6s. The grids of the 6550 were

gold-plated and carbonized, 10 prevent grid emission and bias runaway. The result was more like a transmitting tube, bur at receiving-TUbe prices. �..----�

Like ils grandfather, the 6L6, this \.....,1 tube was an instant hit. Numerous hi-fi GE 6550A, T.","_",,' «

VACUUM TUBE VALLEY ISSUE ·6 • -

THE POW E R K N G S 6 5 5 0 AND K T 8 8

made for a more reliable lObe with greater bias stability. The dad metal was better at dissipating phut heat, and it thus lessened plate and grid emission and reduced hot SpOtS on the plate. popular substitute in hi-fi amps. The first version of the KT88 was shaped in the ST style, similar 10 the Tung-Sol 6550. This short-lived version was soon replaced with distincrivc shout· claim that this tube was made by GE dcn::d-barrclcd envelope. under concract, and a few are insistent that it never existed all! Yet I recall sec­ The first popular British amp !O use :n the KT8S was the SO wan Leak TLSO+ in ing it occasionally in guitar amps during 1957. The first popular American ampli­ the 19805. SyiVOlnia apparently had such difficulty competing with CE for this fier W:I.$ the early Dyna Mark Ill. Other norabla were the Harman-Kardon markct that production ceased in the • uak TL 50� .!..� Citation 11, Mdmosh MC75 and early 19805; I don't recall seeing any that MC27S. And onc of the largest guitar wue dale-coded after 1984, Many were amps ever made, the Marshall Major of rebranded :md sold by. RCA and The ...arly KT88s suffered frolll this, We stinghouse. so thcy wcre built with dad plate /lIctals until the cessation of tube: production at Table I: MOY. There were tWO vCT$ions of the E C ESCAL\TION OF 6550-TYPE 6550A; earlier ones had rough-looking TUBE RATINGS OVER THE YEARS spot welds on the plate, while from about (absolute maximums when givcn. all 1979 the plates were stamped and assuming connection) swaged. There doesn't seem to be a major difference berIVeen these versions, p E Eg2 I'd although the overall quality declined dur­ Ty � p ing the 1980s. In 1984 GE spun off their 6550 Tung-SoJ, 1955 600 400 35 electron-tube division into a separate KT8B Genalu, 1958 800 600 42 6550A GE. 1970s 660 440 42 I company called MPD, which COntinued to produce and sell tens of thousands of The 6550 and KT88 were extremely � 6550As each year until 1991. popular in high-cnd amplifiers during the GmaYx KT88 alld SIIUK'lImgKf88 1970s and into the 19805, including Sylvania wanted to get a piece of this nearly all the models produced by Audio 3ction, so they Research, Conrad-Johnson, Theca and 1967, used fo ur KT88s at 650 volt� to introduced 6550 MFA. The Jadis am s, which appeared in deliver 200 wattS. Although the was their own 1983, were designe:r around the KT88 a tough mbe, operation at above 550 6550A in [he and operated their KT88s in Class A, at volts in triode, near-triode or ultralinear early 19705, It the limits of their di�lpation. Even more connection was very hard on it. The is taller and extreme is the humongous Carver Silver KT88 could handle those operating con­ skinnier than Seven, with its fifteen 65505 per side ditions very easily. the GE, and (fourteen In push-pull parallel with one has q ite differ­ By the 1960s, these tubes had set the � more as a s<:reen-grid regulator) and 375 ent nlH:a spac­ standard for power amplification. So it watts OUtput. ers. But its was inevitable that other makers would plate looks introduce their own versions. GE came For a time, all Marshall guitar amps exactly like the out wilh the str.1ight-sided 6550A in imported into the USA were equipped . e:.trly CEs, with 6550As instead of EL34s, for greater 1971. It was called 6550A, because of the SY/Ila nta 6550 complete with introduction of an exotic 5-ply metal reliability. However, MarshaJJ switched (mnrkd ReA) rough-looking plate material manufucturcd byTexas back (0 EL34s in the Eighties because SpOt welds. In fact, it looks suspiciously Instruments. This metal, produced by their amps using 6550As did nor have the like a Sylvania 6L6GC or 6CA7 with a cladding a copper and iron core with alu­ classic Marshall Mcrunch" sound that so large metal-ringed base. Some experts minum outer layers using explosives, many players demanded. And the numer-

VACUUM TUBE VALLEY ISSUE #6 THE pow E R K N G S 6 5 5 0 AND K T 8 8

Out competi­ 6550 and KT88 Listening Tests �ushe� . • tion, since It was forour I;"coins: twlu:>tionof me.tuba ...."I1K'd COV.p", Oytuco ",be CD feddio=ly in,o a ra,orcd about one-half the SCOIfLK-I50 1"""" amp.nd Klipoch 0.0"" h. price of the GElMPD GIl'SSO'" - &bnc<:d,fa!, rid> midi but ooncr bus 6550A. Eventually and "Ol .. punchy or d ...iled .. the Svt,lam 6S50,. people realized what Det.il,"", Svcd&n.O6SS0B - (disconrjnu l>us.Jam as the SveUana that was more-or-le.ss Lio" Kr88 SV6S5OC. lAu GoU Box, Kr88and E4rly GoU Lion Box shaped like .a KT88. Cnro. KT88- A lotof dyrumic: babnced, ",�, It tOO was inferior, bUI MOV/Genalex 9. GE 6550A .655 4 (3 gd used) grta, bus. richmids, but tom.. ..."''' h.udtrthk . stopped makin Grnola/MOV KTH8_ s"l.and.ng with.",.,.,m but not mud.";g.­ Shuguang 6550s and KT88s returm:d by cnd.,, ,.. .. ion ..MOV KT8&. &bnculsimilar bass 13. Sv�t 6550B3 .746 5 (out of consumers, they pushed for Shuguang to to.. Tuna-Soi 6SSO. produCtion) Shugu"'slChin� KT8.8- Mlnimal weak improve their qualif}'. This happened, but bass, Ta ble 3. mid""'gt: with harsh .nd .ibilan, higlu. r...cksany nOt adequately to meet the severe tkp,h. two dimensional. demands of amps like the Marshall Major Peak Power Test, 500 V Pe:lltOde Besl Sounds: and the Jadis JA-200 and JA-BO. The (arranged by decreasing peak voltage) 6SSO - H.nds down, m. old reliableTung-Sol comes increasing populuif}' of tube hi-fi in the top10, ia balanad, musocaJ IOUnd. OIl' on 19905 has c.aused OEMs 10 demand bet­ I.Svetlana 6550B ...16.67 volts - � �MOV KT88 is ,hotbeK ,hot", ;s. Th� ter stuff. This resulted in the mO:ll muoical with effi:>"I... , rich tonal bolancc. 2.Svedana 6550B3 . .16.33 National/Richardson KT8B, the �Golden Ba, Buy _ Tl>

VACUUM Tu8 E VALLEY ISSUE '6 • THE POW E R K N G S 6 5 5 0 AND K T 8 8 more. Even NOS units in while military SV6550C version. The geller arrange­ surplus boxes arc hOI. RCA, GE, ment was not the problem •• the 8 and Raytheon and Sylvania were all remarking 83 had bias inslability in some sam­ and selling Tu ng-Sols in t c: 19505 and � . ples and some quality-control issues. into the 19605, $0 some WI)] turn up with The SV6550C uses carbonized and these other major brands on them. gold-plated grids, like the original Tung-Sol. In spite of Harman-Kardon's com­ plaint, the original MOY KT88 is an The Shu!uan gs are acceptable, and excellent tuht. It is I1l(cd 10 take more no real prob ems were observed, so vohage and dissip:uion than any 6550. quality control is better than it was a This applies only to the original few years ago. \YJe burned one in on a MOV/Gcnalcx/Gold Lion version, and life-tester with some other types for NOT 10 the current Shuguang version comparison, the results will be posted sold by most dealers. The Shuguang looks in a future issue ofvrY. Sti!], [ can 't like a small imimion of the MOY with a recommend Shuguangs for triode con­ 6550 StrUCture inside. nection or for dissipation above: 30 wailS due to continuing problems NOS �rc very. VERY KT88s hot on with processing. They are cheap tubes, and can the market, bring $350 each if and some very questionable dealers new in the original box. Factory-matched are purting all kinds of brands on a a the by Svetl n . Since the Sovtek dealers can pairs, rccogniuble by paper band them The Sh uan KT88 doesn't . ug g look no longer obtain this tube, it was not around both canons, have been known 10 like the MOV, but th e 6550 is ver)' simi­ available for this test. IfSo,·tek manages sell for $800 in the USA. Rumors abound lar in appearance to later, Tu ng-Sols ""irh find an th factory sra a ng KT88s to o er to produce 65505, that MOV will rt m ki again holes. On lll: e 6 plate Shuguang s glass � ta rs they will be tested as soon as sampl�s �an soon--J've heard [his for 2 years now, and have a noticeable green/brown discol­ be obtained. [t $("ems rhatSovtek distrib­ have yel 10 sce producl. They're gonna oration (rec)'cled beer bottles?), and gener utors may JUSt be carrying ,he regular have serious competition from Tcslovac. flashes in their tubes tend to be excessi"e­ Svetlana produCT in the fU!llte rather th�n ly large compared to the orig!nal The old Sylvanias were provided by a specially-made version, due to finanCIal American and European verSIons. a was Te rry Buddingh of Guitar Pla�r difficulties at the Reflc:<;tor plant th t an making "Sovtek" !llbes. Magaunt. It seems that hi-fi users r dy El's KT90 is known to be a good $CC these, bUI guitarists sometimes hav� a and is tube, popular with audiophiles Wc received fo ur samples of the few old ones kicking around. Note theIr ha"e who used Shuguangs in the past Richardson National KT88s from eXtremely low dislOuion. Ironic that this (and been dissatisfied). This tube is a Richardson's Jerome Cz.akowski. Their tube was used in uitar amps, yet would modified TV g sw«p tube, and it is usable dectrical lest resules were good, and their be more suilable fo r high-end amps. The t is in a 6550 amp. But i not a true 6550, sound was excellelll. These !llbes appar­ peak power was lower than for any olhe� nor sound a 6550. will it like: ently are not in production at this time, NOS Iype, which lends 1"0 indicate that It Unaccountably, our samples had very low although plenty of stock exists in may have been another tube type �v hich much lower distortion at 300v trlode, Richardson's warehouse. These tubes are was modified for 6550 dury. Similarly, than any of the other types ul do. co d more expensive than any of the other cur­ 1 the El KT90 is said 10 be derived from But since these tubes are never run at rentl)'-produced types, and are similar in Ihe PL509, a TV sweep tube. In any case, such low vo es, real-life ltag results do not price to NOS Genalex KT88s. [f you the Sylvania 6550A is definitc y a sca�ce appear here. El's KT99 � . is just a selected have money to burn, want top quality, collectible today, and NOS pncmg WIll KT90, so none wcre tested here. The and can't find any NOS, rhe Nationals be extreme. l1's been more than 6 years future availabiliry of El tubes will fill nce [ saw onc, an stash would the bill. si d Terry's old improve now that the embargo is o\"er b o far r ught back somc nlenlories. As as and Edicron is diStributing their prod­ 4. Out.ro current production goes, the Svetlana ucts. The Shuguang KT99 and KT! 00 6550 ee qua Three The 6550 will be available for th� s ms 10 be the best lity. are new, wc know nO(hing about them versions were tested: the plain B has a concei,'able fu ture. It is a massively popu­ yet. We will try to get sam �es soo�. fbsh has twO gette s :r lar Iype, and there are probably hundreds geller, the B-3 . pill � Teslovac's KT88S appeare In April of thousands of sockets for it in the (the latter is more effecllve at preventing 1996. We gO( twO samples from Terry C world. Its future was looking bleak when gassing), and the had both. All lhree Buddingh of Cui tar Player. These both CElMPD SlOpped production in 1991, use a clad pl:ue metal which is apparently had Groove Tube logos, which is nO( sur­ i but the S\'etlana version and the new different from the CE 6550A mel·al. pr sing as CT's rupen Piuman i a part ! : KT88s are proof thal the Power Ki ngi' These Russian tubes have more peak investor in Tesla. The KT88Ss dId wdl m nt fhe c n power than any others; ,his is due 10 will live on i o 21st e tury. . my 500,' pentode test, and I ran onc OIl good processing during evacuallon, plus 100 m.A withoul any problems at all. Acknowledgements quality cathode materials. The B versions This level of dissipation might be death had some reliability problems, so only the 10 a Shuguang tube. and mOst othe� Than ks to John and Chdrlit for mOll IIf Iht SV6550C er n sold 6550 v sio is being 65505 would show red SPOtS on their old alld KT8814mpln. nmi to Tt,.,., only As B"dJ;ngh forIll( Sy /vallias alld Tts"}/J/l(. Alw today,which has a flash gwer. plates. So Te sla has an excellent product ['vc noted n table, the f/)alllrs to Aspm Pittman of Gt"OOlIt T" lm, i the diSlOrtion B and 1 hope that is uc f l. here it s cess u Jt,,,,,,, Czalrowski "f Ri,ha,ris"fI E':'lfImics, and B3 are out of production. These SlItllllfllI EketTOn Dillius alldAnt/qu, tubes might still be al'ailable from some The So\"tek 6550, which was sold dur­ Elm,,,"i, Supply fo,samplt tuba. dealers, so be sure that you are getting the ing 1992 and 1993, was made (briefly)

VACUUM TUBE VALLEY ISSUE #6 • T EST B E N C H o S C L L 0 S C 0 PES

measure voltage or time from [he screen). The AudIo Test Bench the power supplies mUSI be re:gulaled. Cheaper scopes don't use re:gulation. and so are mainly useful for qualitative. not . "0 ":" by quantltltlVe. measureme:nts. '0001 00 , 0o o0 ® � '7 :11=4= John Atwood The block diagram of a triggered scope is shown in figure 2. The main changes arc in the timeb2Se circuit. The

-- trigger signal, either from the venical = -- Oscilloscopes, Jlart 1 � amplifier or external. is fed into the trig­ ger flip-flip (also called the trigger multi­ Wc have now reached the poim in our vibrator). This is a type of Schmidt-trig­ Audio Test Bench series where wC: will get flip-flop that has a very well-define:d cover one of the mOSt useful, yet ,"omple)!. horizontal amplifiers. This is cheaper and trigger point. The exact point on the trig­ inslrumenu for audio work: the oscil­ felit more stable than D Ccou led amplifiers, ger wavefornl where the sweep is to start loscope. By providing a two-dimensional p but severely disrupts rhe display of non­ is determined by lhe trigger level and view of signals. rather than the one­ re:petitive signals, such as seen in digital rrigger slope controls ahead of the flip­ dimensional view from meters, you can logic. DC-coupled amplifiers, though, flop. The output of the nigge:r flip-flop is gain a much bcm:r understanding of cir­ need balance controls to compensate fOf converted to pulses, and the positive cuit bchavior. Due the large: number of IQ compOnent tolerances and drift. pulse turns on the sweep gating nip-flop. USd for o.Killoscopes, this article will be This enables the ramp generalOf, which broken inlO two parts: theory and oscillo­ A fr ec:-runntng sawtooth oscillator is startS producing a linearly-increasing volt­ scope descriptions in this issues, and applied to the: horizontal defloction age. When the: voltage reaches a pre:­ oscilloscope applications in the next is)uc:. plates. Since this provides a constant de:termined kvel, the hold-olT circuit sweep over rime, this is also called the Theory resets the sweep gating flip-flop, and timebase oscillator. A portion of the verti­ holds it 01T(disabling any new triggers) The: hean of an oscilloscope is a ouh­ cal signal is fo rced into the sawtOQth until all associated circuitS have settled ode ray lObe (eRT). This is the same oscillator where it [ends to synchroni:ze down. At tht' end of the hold-off period kind of tube used in tc:lc:visions and com­ the oscillator 10 the venical signa!. This the sw�ep gating flip-flop waits for the puter displays, blLl fo r laboratory oscillo­ fo rm of injection locking is fairly primi­ next tngger event. scopes, nearly always has electrostatic tive, and only works well on well-defined, deflection r.nher than magnetic deflec­ repetitive signals. A switch is provided to The advantage of thi� complex trig­ gc:red sweep circuit is that sin le or irreg­ tion. The CRT moves a beam of electrons allow a cxternal signal to synchronize the g ular evell1s can be aCCUrately displayed across a fluorescent screen under the time:base. The timebase can be discon­ influence of the electrostatic deflection nected so that the hori:zontal amplifier JUSt as well as repetitive W

(0 the horiromal axis. A saw(Ooth W

VACUUM TUBE VALLEY ISSUE .6 la T EST BEN C H o S C LLOSCOPES

research labs. Their scopes had triggered HMrhkir lO- JO sweep generators, regula[(�d power sup­ plies, and DC-coupled venical amplifiers and 1; ktrrmi"( 545B wen: available. The designs were stable enough that their screens could be cali­ brated in volts/cm and sec/cm. The COIl­ strucrion was excellent, with all bur rhe earliest models using ceramic terminal strips. Their features were aimed squarely ae rhe new generation of television, defense electronics, and computers. Te bronix was ready to become the domi­ nant industrial and laboratory oscillo­ scope manufacturer for decades.

Te ktronix scopes became enormously popular in R&D labs, especially their 530- and 540-serie5 with plug-in venical amplifiers. Dumom was still selling a lot of their old-fashioned scopes, mainly to schools and less-sophisticated labs, but by the late 19505, Te ktronix had eclipscd Dumont. In the early 1960s, DUlllom was bought by Fairchild Insnumems, then faded into obscurity. In the late focus rhe electron beam. This was Tr iplet!, t-leathkit, EICO, and many oth­ 19505, Hewleu-Packard, by then the researched by Bell Labs, and the WeStern ers. These often had vertical bandwidths dominant test equipmem manufactur.:r, Electric 224A was representative of this of 5 MH"l to handle video signals, but stuck its toe into the oscilloscope market. type. Their lifetimes were shon, and the)' W<,;TeAC-coupled, had fairly primitive Despite irs size, though, H-P never over­ had limited brightness. The development recurrent horizontal sweep syStems, and came Tektronix as the largest oscilloscope of an effective electron gun permitted as with their pre-war predecessors, were maker. hard-vacuum CRTs to be mass-product:d, not calibrated. Up until the early 19605, all labor.l!o­ with General Electric and We Hinghouse ry scopes used tubes. As transistor tech­ first introducing them in 1932. These During World War 11, the explosion nology matured, a few all-transistor were shortly fo llowed by tubes from RCA of work on pulse circuiuy led to the portable scopes were made, but Tektronix and Dumont (who bccame the dominant development many specialized oscillo­ and H-P made a generation or oscillo­ American suppliers), and tubcs rrom scopes, most notably the "Synchroscope". scopes using a hybrid technology (mixed Sylvania, National Union, Cossor This was similar (0 a conventional labora­ rubes and ). By ,he early (English), Ediswan (English), and (Ory oscilloscope, but the free-running 1970's, tubes were gone (except, of Leybold & von Ardenne (German). sweep generator was replaced by a trig­ gered sweep oscillator (sce Fig. 2). This course, for the CRT), and oscilloscopes By the late 1930s, oscilloscopes had allowed single events to be predictably became lighter, smaller, and tended IQ started to become a common paft or elec­ captured on the screen. ror general-pur­ have much higher bandwidths. tronic development labs. Horiwntal pose use, the triggered sweep could be In the TV servicing market, American sweep circuits and vertical an lifiers were periodically re-triggered, simulating the companies, such as Sencore, B&K, and being built into the units, an:r their COSt older fr ee-running sweep generator. l-ieathkit were dominant in the 1960s. By was coming down. The pre-eminent Synchroscopes were developed at research the 1970s, though, lower COSt oscillo­ American brand at this timc was Alien B. laboratories during the war, and were scopes starred to become available from Dumont Laboratories. The average ser­ built by Contractors such as Sylvania, Japan, and later Korea and Taiwan. Some vice shop or radio production line did Browning Laboratories. Western Electric, or these were OEM'ed under American not use them extensively, though, since Dumont, and others. After the war, a few brand names, and others were sold under radio tuning and alignmcnt could still be companies, notably Browning Labs, con­ their own names: Hitachi, Kikusui, ete. done with merers. World War II changed tinued sell lilboratory scopes based on (0 These scopes were often near-clones of all [hat. The only effective way to debug the synchroscope concept. However, the 50lid-state Te kuonix models, and as such and align the pulse circuits used in radar, major oscilloscope manufacturers, most had qui(e good fe atures. The build quali­ LORAN, sonar, and many othet wartime notably Dumont, concentrated the bulk ty was good, but reliability of the early systems required the visual display of an of their post-war effort on conventional models was sometimes not very good. oscilloscope. Television broadcasting, recurrctl(-SWCCP designs. These types or scopes dominate the low­ started in Europe before the war, and JUSt COSt analog field today. after the war in America, also rCXjuired Two engineers who had worked with synchroscopes during the war were des­ oscilloscopes for iTS pulse circuitry and In the 1980s, some specialty oscillo­ tined to change the oscilloscope land­ �sweep� alignment of the RF and IF sec­ scopes were developed that digitized the scape. They fo rmed a company in their ,ions. The result was an explosion of low­ incoming signal, ,hen displayed it on a native Portland, Oregon to build high­ COSt oscilloscopes aimed for the service computer-driven display. These were quality oscilloscopes based on the labora­ and hobbyist market. Common brands expensive and had fairly low bandwidths tory needs they saw in World War 11 included RCA, Sylvania, Simpson, initially, but permitted better viewing of

VACUUM TUBE VALLEY ISSUE #6 • T EST BEN C H o S C LLOSCOPES

transi�nt �v�ntS and allowed compU!�r signals will be observed. Some scopes, sw�ep, which pumits the'. sweep 10 start analysis of the signals. H-]> and Tekuonix especially new�r solid-state ones, have after an adjus13ble delay time. Thi s is not

sold th�se Digital Sampling Oscilloscopes limited maximum inpul voltages, such as tOO useful for audio testing, but can be (DSOs) along sid� their analog models, 20 V/cm or 200 volts maximum. Unless helpful in digital debugging. but as the COSt of digital technology fe ll, used with a decem XIO probe, these lh�s� became dominant, and today scopes can be'. blown OUt when measuring Your budget will de'.termine the clas� uf Tc ktronix has juSt a few token analog typical vol13ges in tube C{juipment. If you scope you can buy. If it is unlimited, scopes in its product lin�. are measuring over 600 volts, you will microprocessor-controlled analog scopes need special high-voltage scope probes. or adv;l.nced digital scopes are available. Low COSI hand-held DSOs using LCD However, e'o-en the best of these do not displays are currently made by Fluke, If possible. get a 2 (or more) channel have the pin-point clarity or smoothness Te ktronix, and others. Th�se, along with scope or a dual-beam scope for your test of operation of some classic analog scopes. desktop DSOs, are potentially auractive bench. This allows signals to be corn· If you have 5200 to S600, a good used for somCCln� looking 10 buy a new oscil­ pared. A tWO channel scope works by solid-state Te ktronix or H-P scope or a loscope. However, di gital scopes ha\'e lit­ ei ther r�pidly switching the electron new Asian oscilloscope can be purchased. de or no capability fo r trace intensity beam between the channels (the achop� These are small and reliable, although do modulation, and can often miss subtle mode) or alternately sweeping each chan­ not hal'e the fine traces of the bigger tube:­ events that occur amidst repetitive events. nel (the Malt" mode). The chop mode is type scopes. At the opposite extr�me, for Being somewhat of a traditionalist, and usually used for lower fre(luencies, and $5 to $25 you can pick up a simpl� hob­ giv�n the low COSt of audio-capable ser­ The air mode is for high frequencies. Both byist or serviceman's scope at a swap meet, vice scopes or us�d scopes, I recomrnend of these modes can someTimes cause odd but aside from being of poor quality, they an analog scope. behavior. especially with digital signals, so often need repair work. For 525 to 5200, a lillle experience is needed when using professional-quality tube-type scopes and Choosing a Scope this. A dual-beam scope'. has actually twO cheaper used solid-state scopes are avail­ Viewing audio signals is gcm:rally the separate electron guns with SeparaTe \'erti­ able. The older scopes may need repairs leaSt demanding task of all the things cal amplifiers and deflection plates. Both and alignment, but if you can get the beams are swept by a single timebase. technical manual, you may be able to oscilloscopes can do, so nearly any oscil­ This is more expensive. but has the'. least work on them yourselves. Getting scopes loscope can be used for audio testing. However, convenience, accuracy, reliabili­ ambiguity between [races. Single channel, r�paired professionally can COSt hundreds ty, and COSt need be considered. We singl� am scopes arc useful for simple of dollars. 10 mOllltorlng.� will first look at the raw technical specifi­ A probkm with most older tube-based c;.nions needed, then the general type of Many old.:r OSCillO)cO es have poor oscilloscopes is that they are large, put scope, and finally. some specific models. sensitivity for the eXternar horitental out a lot of heat, and can be noisy (from The primary oscilloscope spec is the input, compared with the ve'.rtical input, the cooling 13n), This is why they are venkal channel bandwidth. A rule of and most have poorer frequency response often for sale cheap. If you can handle thumb is for the bandwidth to be at lea)[ for the horizontal input. If you need to this, though, you will get a scope that can use have excelle'.nt resolution - far better than 5 times the maximum frequency to be the X-Y mode, look for a scope with tested. For most tube-type audio systems, good horizontal sensitivity or one Ihat modern high-speed scopes - and arc elec­ allo� a second ve'.rtical channel 10 be trically very rugged. They can have a lot I M Hz or even 500 KHz would be enough. Really broad bandwidth systems configured as the horizonTal channel. of tubes - from 15 to more than 65, so would require several MHz. If you are make sure the tubes arc good, or ,hat you have a good supply of 6DJ8s. Re-tubing looking at digital signals, though, you Httllhkit 10- 12 may need 50 MHz or more. The maxi­ at retail prices can be really expensive. mum sweep speed in each scope is gener­ Audiophile.quality tubes arc not needed, ally commenSUrate with the maximum I though, in mOSt cases. v�rtical bandwidth. Representative Oscilloscopes An AC-coupled us(illuscope is quite (Note: These are scopes that I am usable for most audio signals, but DC fa miliar with. Many others may be quite coupling ("direct coupling�) insures that suitable, so use the criteria given above low-frequency signals are nOt distorted by for selC'.Ction) the scope's low-freque'.ncy cut-off. There are not many of the recurrent­ The greater the sensitivity, the bener, swee'.p scopes that I ha\'e fo und to be very for audio applications. This is especially good. Of the kit scopes, the Heathkits are tfUe if you use the ux I O� attenuated generally the best. A DumOl1t scope in scope probes (n.'ConHllended), since they good condition may be useful. but avoid CUt the input by a 13ctor of 10. Most gen­ the ones with PC-boards - they arc unre­ eral-purposc scopes go down 10 10 liable. Some good compact scopes include mv/cm, but a fe'.w go as low as 200 the Heathkit 10-10 and the Waterman !lV/cm. Some scopes have DC coupling portable scopes. down 10, say .1 V/cm, then have AC cou· pling for the lower ranges. Some other Sencore'. and B&K made a series of scopes have testricted bandwidths on the As mentioned earlier, a triggered .wlid-state serviceman's scopes in the high-sensitivity ranges. These trade-offs )weep is recomme'.nded. An enhancement 1960s and 19705 that perform decently,

are not tOO bad. since most of tim� large 10 the triggered sweep is The delayed

VACUUM TUBE VALLEY ISSUE .6

- .: T EST BEN C H o S C LLOSCOPES although have questionable reliability. By two-channc:l the 1980s, mon of these models had been scope is recom­ replaced by Japanese-built ones that were me�d as your better quality and more reliable. mam scope.

Of the labor.uory scopes. the bcst is One of my TekHonix. Nearly all of [heir scopes arc favorite Tek good, hut there arc some ch,lt "re: either scopes is the 502. very common, or stand OUI as being espe� This is a true cially good for audio work, which will be dual beam scope mentioned here. with excellent sensiliviry (100 The "mainframe� plug-in scopes: [he or 200 IN/cm). 531, 533, 535, 541, 545. and others, It has about 1 were built frolll 1955 10 the early 19705. MHz bandwidth They are large and noisy, hut have a on mOST sensitivi­ tremendous variety of vertical amp plug­ ties, which [ have ins, ranging from ultra-sensitive audio fo und fine for channels to spectrum analyzcrs. They are audio use. It also common, and u5IIally fa irly cheap. For has true differen­ best reliability, get oneS that wefe made rial inputs (good from {he: early 1960s or tHer. Look for for measuring in ones with embossed blue metal �skinsM, the presence of nOl ones with brown or blue wrinkle common-mode paint. Before about 1961, all Teknonix noise) and can be: scopes used the infumous Sprague switched so that kstriper" capacitors and paper high volt­ one channel can 50lA age capacitors, both of which tend to go dri\'e the hori­ Ttluronix bad. Many c;lrly ones used sc:lenium recti­ zontal deflection fiers, which also deteriorate. I have also plates, The 502 is somewhat odd in that bandwidth is lOO MHz, the 475 went up run into problems with open-circuit it has no continuously variable deflection to 200 MHz, and the 485 went up to metal film resistors - usually either the sensitiviry or timebase controls. This is 350 MHz. Because of their populariry, orange-brown �Tl� brand or the light not tOO difficult [Q live with, but is recti­ they still command a high used price. As blue striped ones. Other than these prob­ fied in the 502A model. The 502A also with most small high-bandwidth scopes, lem areas, I've found tube-type Tek has better sensitivity, a single-sweep fea­ they used "mesh-expansion� CRTs which scopes 10 be remarkably rc:liable. ture, and a front-panel control to balance limit the minimum spot size (they do nOt the beam brightness. Later models of the have crisp displays). However, if you were The second generation mainframe 502A (after about 1965) replaced the all­ to own a single oscilloscope to handle Tektronix scopes, the 560-series, built tube vertical amplifier with a hybrid PC­ both audio and digital, these can't be from the early 19605 to the 19705, arc: board, which, although more stable, uses beat. Low'cost fo llow-ons to these modd� bettef suited to the audio test bench. hard-tO,find 8056 . were the 2213 and 2215. The early mod­ They are smaller, have no fan, and have a els of these laSt two had power-supply good selection of plug-ins. They span the reliability problems. tube-tO-transistOr transition, with the early ones being all mbe, and the last In (he 19805, Te ktronix added micro­ ones being ali transistOt, and hybrid cir­ controls to their portable cuits used in between. scopes. The best-known models are the 2435, 2445 and 2465. These can make The final generatioll ofTc:kuonix on-screen measurements of voltage, time, mainframes was the 7000-series. These and frequency, and can save control set­ are high-performance solid stale models ups in memory. Tek's mOSt recent low­ from the 19705 with bandwidths up to COSt analog scopes are the TAS 220 and 400 MHI and many complex plug-ins TAS 250. available, These would be good for digital use but are overkill for audio. These are Hewlett-Packard's tube'type oscil1o­ beginning to come OntO the market as �copes, such as the 130, 140, 150, and surplus, but beware: a bad rype of plastic 175, are quite useable, but, fe ature-for­ was used in some of the rotary switches, fe ature, lag equi\'alent Tekuonix model�. especially in the timebases, that deterio· If you stumble across a good one, thar's rates and breaks, and cannot be repaired, fine, but don't go OUt of your way for Make sure all the plug-ins work before them. They mostly used PC-board con­ buying them. . struction (something Te ktronix ;J.\'oided Probably the most f unous and well­ until well into the so li d-state era), which Te ktronix made: a varie:TY of �ponabk� liked Te kuonix scopes are their solid State can be a reliability problem with older and lower COSt mbe-type scopes, such as portables: the 453, 465, 475, and 485. tube equipment. H-P's scopes gOt better the 310, 316, 317, 503, and 515. These Of these, the 453 and 465 arc most suit­ when they wtnt solid-state. Thtir 180- single channc:l scopes work well, but a ed to general audio work. The 465'5 series mainframcs were quite good, and

VACUUM TUBE VALLEY ISSUE #6 .. U N C L E E R C • S DUMPSTER the l:uer 1700-series low-cost scopes are huge Clthodes. Around 1954. Ihe plate decent. although. again. not as good as Uncle Eric's Dumpster sltucture was changed so the axis of the competing Tck scopes. Many engineers tube elementS was perpendicular 10 the complain ,hat H-P scopes never triggered The 5687 Tu be Family plate flange. resulting in more plate are�, as well as the TekuoniX' scopes. H-P was and a StrOnger construction. All other one of the first companies to use internal By Eric Barbour companies used this plate Structure for graticules. which gives more accurate dis­ 56875, and in !hc 1960's Sylvania adopt­ plays. ed il for their 12AX7 and 12AV7 types, as well. Aside from the lOW-COSt Asian This uril!s ()f artidu is inlmdl!d t()focus imports. Other imports Ken in Americll a sp otlight on tubl! tYpl!S which arr com­ The 5687 was imended as a high­ are English brAnds such as Marconi and IransconduClance dual triooe for generAl monly ignorrd l()dny. Many things wur Telt'

Bibliography

Greenwood. Holdam, M�.:nu;,

El ectronic in$l[umems (MIT Radiation Lab Vol. 21). McGnw-Hill, 1948, pp. 576- 664. D.:tailed descriptions of synchro­ scopes, etc.

Kdler, TheCal hude R"y Ty be,l'elef TechnA. ology. HiSlo[yand Al!p.l i(;ltioos, Pali�des Press, 1991, Compre hensive hinory of the mbe. Many photognlphs . fe ct for audio. In many cases. a type "''as tube. RCA's 5687 is probably the mOst used for economic reasons. \'(fitness che desired, because of the general aura of Rider, Uslan, Em;ydopcdia uo 12AX7. If you don't necd extremdy high m�gnificence surrounding their "black­ C' !lhode RayOsc illoscopesand Their plate� tubes. RCA's early 6L6GC, .llln.2nd Ea., John F. Rider Publisher, gain, but DO wam low diswnion and a 6V6GT, 5751 and Olhe� were also in Ihi� Inc" 1959. Enormous book on all aspectS dean sound, the nearly-forgocten 5687 and its kin are worth a serious look. sought·afler series. of oscilloscopes. Mmy scope schematics. Many experts (botb real and virtual) Soller, Starr, Valley, Cathgde RayTube The 5687 was introduced in 1948 by fed Ihal high tr.lIlsconductancc makes a Displa)'l (MIT ItIdiation Lab Vol. 22), Tu ng-Sol as a member of the so-called McGraw-Hill, 1948. Detailed info on CRT KARINe" tube series, imended for use in r------, technology and support circuitS. commercial avionics. Tung-Sol, GE, and Raytheon originally ill1roduced the Stall Griffiths, W7NJ, Oscjl!QSCOPCSj ARINC types, although Sylvania and . Selectingand Reslorin,a CI;Wic, priva te­ RCA also made thcsc types. All of these . - . I ly published, 1992. &rvice hints and companies, as well as some fore ign com­ ..... the ".1. •. descriptions of allTe ktronix scopes up IQ panies, made 5687, By lhe late .. 1970. (Ava ilable from AntiC:jI.lt Electronic 1970s and 1980s, only GE and Sylvania Supply). (later Philips ECG) were making the f l , " 5687. 'lektroniX', [nc., Typical Qu,iIlQKop'

CircuitQ',TekuQnu;, 1961. Excellent The firsc 5687s by Tuns-Sol had a '...... !!/'•• 11' description of tube-typc le ktronix circuiu black carbonized pl:lIe in the identic�l il; - for the tcchnician. shape of the 12AU7s of the time. An easy way to tdl che difference was the 5687's RaJIMm (m4 Tolhiba 5687$

VACUUM TUB E VALLEY ISSUE # 6 • U N C L E E R le'S DUMPSTER

good tube, to the exclusion of olher fac­ Warning! Don't plug the tors. DespiTe Ihis, the 5687 has low dis­ 5687 or its cousins intO GE 7370 and Rl'd&l1Ik 6900 tortion as well as a Gm of 8500 flmhos, 12AU7, 12AX7 or similar ffi:lking it a very clean-sounding tube. sockets. The pin connections The rew people who have experimented are different, and damage to with it agree 1ha\ it is a sleeper. Later the tube and your equipment developments included the 6900, inuo­ will resuit! duced by Bendix in 1957, It was the Red Bank version, wilh gm =11,500 and Sound tdtS revealed that extreme ruggedness. Then came the GE tbe 5687 is vcry consistent 7044 of 1957. with gm ,,12,000 and less from brand to brand, but ruggedness, imended for calhoJe fo llow­ there are slight bur detectable ers in computing circuits. The 7370 was a sonic �signatures" to each 1959 GE version with a 4D-volt heater brand. The older Sylvanias for series-string use, and the obscure and GEs were very clean and "lung-Sol 7892 (1961) was intended as a smooth, while the RCAs had high-current pulse amplifier version. A the typical soft, gauzy quality European version of the 7044 was the of aJJ RCA black-plate types. E!82ee, introduced in 1958 by PhiJjp�. And recenT Philips military ing the high transconductance and high I! was a premium type with a large plate surplus 5687WBs were notably harsher petveance that make them technicaBy and more excellent classics. If you have a srock of Dutch Amperrx PQ and fau USAmpl'7?X 7119s detailed than them, use them in your own homebrew the others. equipment. Do act quickly, though, and An NOS Bendix Red Bank 6900 gave a mel­ low quality, similar to the RCA but less pronounced.

Large calhodes and 9H careful man­ 5687 BasfDiagram ufacture make these stash away a lifelime supply; these types tubes suitable are disappeanng rapidly. The only one for audio still being used by the U.S. government is use, especial­ the 6900, and even that is declining in ly as cathode numbers as old avionics are scrapped.

______fo llowers or L ______MU still manufactures it in occasional , _ --' for line-level lOTS, making it one of lhe very few receiv­ stages. The 7892 was a remarkable device structure and a gm = 15,500 flmhos at 36 ing tubes still in production in the USA. ma. This type was brought into America for its small size; il is rated 10 produce 5 as rhe 7 [ 19 by Amperex. Some later Illili­ amperes in short-dury-cycle pulses. All If you have experimented with any tary 71 19s were built here. the 5687 types arc similar in general ral­ unusual tubes {hat have worked well in ings to the 6CG7 or 6SN7GT, while hav- audio applications, let us know.

Condensed Tu be Specifications: Get 6FQ7 128H7 5687 6900 7044 7119 ...... 6.3 [2.6/6.3 12.6/6.3 12.6/6.3 12.6/6.3 12.6/6.3 V Eh' Hi.gCheck out vrvTone on-line at Ih: ...... 0.6 0.310.6 0,45/0.9 0,45/0.9 0,45/0.9 0,410.8 A M�. ....330 300 300 600 300 300+ V Er' www.vacuumtube.com M�. I'd (ea. section): .4 3.5 4.2 4.25 4.5 4.5 W -library of Tube-Related Articles mu: 20 16.5 17 18.5 21 24 -On-line Tube Audio Buy/Sell Ads gm: ...... 2600 3100 8500 11500 12000 15500 f1mhos -Cool links to other Tube Sites r : ...... 7700 5300 2000 1700 1750 1600 ohms p -Subscribe to VTV + get all issues at: ' .....250 250 180 120 120 120 V Vp using your credit card V ' ...... �8 �IO.5 -7 -2.0 -2 -2 V g -Order Big Tone T- Shirts and other 1 • ..9 11.5 23 36 36 36 mA P (sources: GE Essential Characteristics, goodies [>hilips Miniwau Pocket Book, Bendix Ad.) www.vacuumtube.com

VACUUM TUBE VALLEY ISSUE #6 • HI-FI SPOTTER'S GUIDE SERIES

----- B

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2. VINTAGE HI FI SPOTTER'S GUIDE - VOLUME 2 This Volume covers equipment nor listed in Volume I. Almost 500 amps, prearnps, runers, ere are depicted. This edition covers early audio, Golden Era (1947-63) and includes a "Speaker Sponer" section with Airec, EV. JBL, Jensen, University and more. $18.95

VIKTAGE HI-FI 3. NEW 1997-98 VINTAGE HI FI and PRO AUDIO PRICE GUIDE PRICE GUIDE New, updated price guide fo r vintage hi fi amps, preamps and runers. • 11197-98 Now includes Vintage Ahec, II'C, JBL, ReA and Western Electric pro audio and [hearer gear. Also, home and pro loudspeakers, N.O.S. vacuum rubes Q � and audio transformers. Over 1600 items covered with grading and collector �,� � information. Corresponds with Vo lumes I and 2 of the Spotter's Guides. $25.00 4. "VINTAGE HI Fl THE GOLDEN ERA 1947-65" A one-of-a kind video covering the nostalgic post-war and 19505 home hi fi era. Over 80 classic audio amps, tuners, erc are shown. This video is professionally produced and is 34 minutes in length. VHS NTSC $25.00

THIl .·LT.,.ATIl 5. THE ULTIMATE TUBE SUBSTITUTION GUIDE T,·.e 1I.·..... lTrT ••• No tube electronics emhusiast should be without this book. ...• .. '111 Over 10,000 tubes are listed on 240 pages including: audio, radio, transmitting, and special. Also fe atures an audio tube section with VIDEO tu he evaluation and tCHing information. $29.95

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VACUUM TUBE VALLEY ISSUE # 6 Original Vinyl Sound

Va cuum TubePhono- Preampli(ier

• True RlAA Equalized

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• Gold plated ReA

• OF boost switch

• Low Distortion

• Low Noise

• Drives PIA direct

• Designed & Made in USA

• Superb QuaJity and Sound

• Operates on IOO/115/230VAC

• Tube shields (not shown) are supplied

Technical Spetifications Model PP-l Model PP-IH

Voltage Gain 40dB min @ 1kHz 56dB mi n @ 1kHz Variable Gain Adjust Range Fun gain 10 -85dB Full gain to -85dB Frequency Range 20-20,OOOHz 20-20,OOOHz Equalization (2 positions) RlAA or HFboost RIAA or HFboost Input Impedance 47K Ohm 47K Ohm Output Impedance I K Ohm lOK Ohm Hum & Noise Output Less than .6 mY Less than 3mV ChatUlel Separation -60dB at 10kHz -55dB at 10kHz Sensitivity (at 1kHz) IOmV for line output 1-2mV fo r line output Maximum Output 7V RMS 5V RMS Heater Voltage 3 section DC filter 3 section DC filter Tube Compliment 3 each 12AX7 3 each 12AX.7 Level Adjust lndividuaJ channel adj. Individual channel adj. Connectors Gold plated RCA Gold plated RCA Primary Requirement loo-230VAC IOVA loo-230VAC IOVA Size (W xLxH) 19 x13x5cm(7.5 x5x2") 19 x13x5cm Weight 1.8 kg (4 Ibs) 1.8 kg (4 Ibs) Finish (2 choices) Black or Chrome Black or Chrome List Price (assembled) $469 black, $489 chrome $479 black, $499 chrome List Price (ki t) $379 black, $399 chrome $389 black, $409 chrome ********Call US fo r Factory Direct Discount******** http://www.amemura.comlsoundl Antiqu e Sound" USA 6717 NE 181 Street, Seattle WA 98 155 USA, Phone 206-481-8866, Fax 206-485-3836

VACUUM TUBE VALLEY ISSUE # 6 • GO AHEAD Ask top engineers and music lovers worldwide what capacitar they choose for their ultimate designs,

11 0 v---b----A-NI--EDI--­

MUSICAp@ The most naturally revealing capaCitor. Film and foil polypropylene construction - optimized for fine speakers and vacuum tube electronics. Precision made in the USA.

Va lues from .01 pF to 10 pF. Listen and compare for yourself.

lbis is the same amplifier built in the �AudiQ From Tu bes" class taught by John Atwood at theRa ndall Museum in San Francisw. Available UPGRADE NOW either completely assembled or as a partial kit for the SCriOU5 constructor. "Your capaCitor artistry is profound." Horvey "Gizmo" Rosenberg Sl�r�, .ingJe-endtd .mplir.�r. with lJ watt. (RJ\IS) per channel • 3 db of f�dba<1"'un chan".I$, with choke fl ltc"n� All For more information and to purchase, contact these • tub< d<'$ign (no �rnicondu"ors anywhere) qualify distributors; Allpo int-to-point wiring (no PC bo.,d$) • Welborne labs. USA 303-470·6585 • Wrinkle powder·real finish in tither dark Sr>Y or bl",k (o'h�r fin"h.; .vailabk bysp«ial order) • The Parts Connection. Canada 8()).769-iJ747 • Michael Percy AudiO Products. USA 415'669·7181 Special Introductory • A & S Speakers. USA 510-685-5252 Price: $ 1 395Ia.. embled) one electron '" • Handmade Electronics, USA 610-432-5732 G)65 Washington Sire". Suite • SJS Electroacoustics. England 44-1 706-823025 $595 Ip"o1;,.t kil) n7 s."ta Cl ... , C.lifornia 95050 USA • Tang Hill International ltd .. 886-2-5813605 F.O.II. Sunnyval<. CA FAX: 408 985-2006 i Contact On� EI..:tron �EMs and international distr butors may contact hllp://w-..w.onc·d

ur GT·KT88s r-----, O flllW r----, Our new GH.4ls by 1I�\U)".\t\'� by rUL�'Id\'· The first teoitimate This totally new European KT-a8 maae desig(1 u�rades ana In 30 ylla[s. This rep�s.1t EL34 appll(:aUons. newly de�oped bum producing mOre power. power tube t1as wider 1req!l!ncy response and specilll heat disper�iOfl dynamIC flInge than �ny other EL34 wings wekied tot he paS! Or prtsent! This new tutlo plate stfucture to hetp also has special neat dispm,on keep the tube's audio WIngS to improve the audio pertormance stable at rt!SjlOOS!!at higller power high power handling levels and Gold wOIInd grids �els and Gold wound lor improved fidelity. grids tor improwd Availablt irt fidelity.Av ailable in Blue and Red Glass.

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VACUUM TUBE VALLEY ISSUE # 6 • It's Like Music to Yo ur Ears ... Amperex

Bugle Boy audio tubes are back and they're betterthan ever! When it comes to seleding premium audio tubes for your amplifier, accept no less than the best, Amperex Bugle Boyl Amperex Bugle Boy tubes are burned in under full load with all voltages applied for 24 hours before being tested ....- - for noise & microphonics. The aging racks used are from the original Amperex production line built in Holland decades ago.

Complete test results are supplied with each tube, including plate current, screen current, grid one current, filament current, and total harmonic distortion (THD). The THD measurement Is performed using one of the finest spectrum analyzers available - the Hewlett Packard 3561 A. Matching in pairs, quartets a octets Is available for all tube types.

Special test requirements? Not a problem. For a slight additional charge we will test and match to your specified operating conditions.

Types available: 6DJa/ECCaa, 12AU7A1ECCa2, 12AX7A1ECCa3 and many more!

So if you haven't dealt with a source capable of meeting your demands, call us at 1-800-TUBE USA or call 630-208-2200 today for information on additional products and the worldwide locations nearest to you. You'll liKe what you hear!

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ova30 years.new This beam.power tube has replaces all EL34 appliC

bly Our nc:wpmnwmftSlWM'\m, E83CCs pa:amp tube- with Great attention isgiven to materials and assem withover 30 """" liom<,.;l<.wound '"'" gold ,.;,.. hdp ro mKro­"""" handcontaCtS welded inthissinglcdual uiodc!ThisgeatSIOund­ phoruc1IIrmaKmS, lowernoise, and im.pRll'le both traNient and ing new tube replaces the 12AX7170ZS in allapplicatio ns. Ikqua>q- (T_ pNamJ• iI GT .NnnI..,..;.,., GT.£CC&J)

12866 Sylmar 21113 Superior CA 91311 USA foothm BIvd., Street, Chatswortil e ClliIomla 91342 USA Tel' (800) 421-4219 or (818)882-3872 " Te l. (S18) 36H500 "" (818) 385-11884 "" (S18) 882_ �&t.aJ_ e-maII=:.Groovel\JbB @ AOL.com CJI"'Dnip�:e-mail: PentaLab"710AO:: ::L.com '::t:: Opri«� ...... tU..,.",,;J&f- V�J{Jt)B C.ll:Ak BL\. YVjuu� ..It: I jU� _ll:",k ...... 1;) L v\.t t:I 't I::

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UVt:> AI{ Jt: B cAR lc.'R .,. 1.. 6 K. t AR � _E:..... v I b �o .\ 0 r- .L R � [ I:. t t PHONE: 303.470.6585 FAX: 303.791 .5783 \ '8 ' , E·MAIL: [email protected] WEBSITE: HTTP://WWWWELBORNELABS.COM }O l? Design In the "Real McCoy"

3 to 280 Watt Tu be Output Tra nsformers Power & Filament Steel Cages Tra nsformers

Chokes (open & enclosed)

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= �liw :..-- ClClassicClComp onents from: 4£:!!s,. tssa.. We've been in the transformer & enclosure business for ...... HAMMOND over 70 years. In fact, most of the components shown here have been in continuous production since the � MANUFACTURING," Trust your design with our experience... 1950'5' IrI,"www .hammondmfg.com 4700 Genesee St., Cheektowaga, NY 14225 Phone (71 6) 631-5700 Fax (716) 631-1156 394 Edinburgh Rd. North, Guelph, Ontario N1 H 1 E5 (519) 822-2960 Fax (519) 822-0715

la Svetlana Audio Tubes

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.0\ "The S)'etluna (SV)6550C bem Ihe pams off lilytreasured TU lIg-Sol t:oke hortles, bass was tighter and more defined. nte 71l11g-Sols had a filfle 100 much bass, Ihey were too chesty alld llIbby by t:omparison" Dan SchmalJe Publisher. Valve Magadne

"To ollr ears. Ilu: be�·t mum/ins EL34 of the Ill­ g/"Oup W(IS Svetlalla's Gold Top EL34. W POII'er 1i.lbe Tmu Te s/ Guitar Pbyer 1\bgazine November. 19%

II'(b ;ule Jls/ribllwr V'$1I "UT cldljo,." " t,,'yuu.' .. "" SveELECTRONtlana DEVICES

HeadQuarters: 8200 S. Memorial Palkway • Hunls�ille, Al35802 • phor.e (205) 882�1344 • tax (205) 880-8077 3000 e 94028 • (415) 233-()429 (415) 233·()439 Markeling & Engineering: Alpin Road · Porlola Valley, CA phone • fax www_$vetlana.com • WE HAVE ENOUGH COMPONENTS TO BUILD A SMALL CITY TUBES: PARTS:

Over 3500a udio,receiving, transmitting and industrial types Resistors, tube sockets, chassis boxes and in stock, including many foreign and early types.We offe r aluminum enclosures, knobs. dial belt, lamps. diodes, speakers, the complete line of Svetlana audio, amateur wire. phonograph needles and cartridges and much more. radio and industrial power tubes. LITERATU RE: TRANSFORMERS: Extensive selection of literature and books and tubes. Hard to find power, filament and output hi-fi equipment. circuits diagrams. communication transformers as well as filter chokes gear and antique radios. Some items for tube �uipment. We not available elsewhere! feature HAMMOND. One Electron, MagneTe k and Thordarson as SUPPLIES: well as many new old stock Grill cloth, transformers. cabinet CAPAC ITORS: restoration

High voltage electrolytic and supplies. mylar capacitors, multi­ batteries. chemicals, section capacitors and tools. test meters, more for tube circuits. gifts and kiu.

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HAMMOND MANUFACTURING. G)one electron'"

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