VACUUM TUBE VALLEY'·
Published Quarterly Celebrating the Hisfory cnd Quality of Vacuum Tube Technology Issue 4 Volume , Price S8.00 Spring/Summer 1996
Happy 60m Birmday to the 6L6 The history and test results of this legendary audio power rube Page 3
GE, RCA and Sy/vflllia 6L6GCs
Hanllon-Kardo1l Citation 1I
In This Isslte...
Editor's Page 2
6L6 Forever: History and Tests 3
VTVListens to 6L6 Types J I
Wby 88 to 108 FM? 12
HKCitation I and 11 15 Classic Vacuum Tube Manuals 6L6 Cutaway vrv GE, RCA, Citation 0Modificarum 22 reviews Sylvania, Tung-Sol Vintage Bookshelf Speakers and other tIIb.:: manuals by era and An examina tion and listening evaluation of mbc manufacturer rage 26 Designingfor Sound 23 the most popular home hi-fi bookshelf loud speakers from 1955-1972 Page 28 Ntws 25 Tube Industry Early FM Broadcasting A Banle of the FM Bands between [he beau Review of Tube Mamtals 26 roerars, broadca5ters, and manufacrurers in rhe 1940s Page 12
Vintage BookshelfSpeakers 28 Vacuum Tube Valley is published quarterly for electronic enthusiasts interested in the Audio Test Be,uIJAC Meters 33 colorfvl post, presentond future vacuum01 tube electronics.
Wri".n and Produced in !h. Un;",d.. 51" of ArneriCl E D TOR' S P AGE
Technology dcparunem. John will ((
EDITORIAL STAFF '" Copyrig,t 1996 Vacuum Tube Valley Vacuum Tube Valleyis published quarterly 'M and Big Tone All righb re�. e for el droni c enlhusiasts interested in Ihe Charles Kittleson - Editor and Publisher No port of Ihis ptJhlication may be reprinted Of colorful past, present and fuhJre af vacuum Tec ca otherwisereproduced hJbe electronics. John Atwood - hni l Editor without written pemtission of thepubli�r. Eric Barbour - Associote Editor Subscription is US$32.00/yeor 14 issues} Send circ ulatioo and editorial $40/Canodo and $45/A�ia and Europe Dove Wolze - Audio Consultant correspondence to: CASH, US BANK CHECK, CREDIT CARDS Vacuum Tube Valley Steve Porr - ArtDirector 1095 E. Duane Ave., Suite 106 To subscri be, renew or change address coli Julie p, Wemer- CopyEditor Sunnyva1e, CA 94086 USA or FAX us at (408)733-6146. [email protected]
VACUUM TUBE VALLEY • 6 L 6 FOR EVER
6L6 Forever 1936-96 60 Years ofAmplifier Service By Eric Barbour
If you ever find yoursdfbeing harassed by techics who insist upon criti ci'ling you for your interest in vacuum tubes, there is an casy answer. They can be silenced with a simple As ofMarch ! 996, the mighty 6L6 is celebrating its 60th birthday. It's still being manufactured in Russia and China. And its popularity in guitar amps is assured for the wnceivable future. Various "expens� in the rnainstream elec tronics industry, who relentlessly kill old technologies and curse people who use them, can do nothing about the 6L6 � it continues to be a dominant voicemaker of rock'n'roll guitar. Many Uexperts" have (fied to simulate Cutawayof the 6L6 guitar amp with various semicon 6L6 Beam ductOr-laden gizmos, from complex ana StrucNlreby log computers to OSP chips, with varying Ke1llLeech technical success, and with linle or no financial success. There are numerous companies making 6L6 powered amps today. Fender, Mesa-Boogie, Ampeg, Peavey, Kendrick, Victoria, Soldano, THD, Louis Electric and many others have staked some of their product lines on the 6L6. So don't accept the muttering ... about "dead technology. " NOW you can get full I. History 60W.tt, from 0 poir of 6L6's In 1931, rhe audio outputS of radio sets were dominated by [riodes such as the UX-171 and UX-245. But even [hough push-pull 245s could produce 5 waHS easily, there was ongoing pressure from manufacturers for ever-more efficient OutpUt tubes. The pentode was the answer at firs!. It originated in Europe, with the first American power types being the Champion P-704 and Arcturus PZ. These were very early types and had some reliability problems. They were quickly superseded by ReA's UX- Ellriy 6L6 Amp VACUUM TUB E VALLEY 6 L 6 FOREVER RCA 1614 IlIId6L6melnl wbes 247. rdeascd June !931. Suddenly you could get 2.5 watts out of a single [Ube, with easy drive requiremencs and al only 6L6GX (Isolallliu bti#) alld6L6G 250 volts! Millions of radios used thl'; '47, and its descendant, the 42 with its 6.3 volt heau,'r, was even more popular. The 38, 48, 59, 2AS, and 6F6 followed, as did European types such as the Mama AOPen, Cossor MP/Pen, Osram MPT4, Mullard PenA4 and numerous olhers. BUI RCA engineers were pursuing more: lofty goals: low distonion with high efficiency. They were developing special power [etrodes, such as the 46 (intended for Class B push-pull and giving 20 waItS from a pair) and the smaller battery-set types 49 and 52. Late 1932 saw the 48, which was intended [0 have its screen grid connected only as a scr�n grid, nor in parallel with the control grid as in the 46. A similar dcvdopmclII in Britain was grid dri\'� vohage. Th� third problem is the Hivac �Harries·. But the 48 was the that the capacitance b�tween the plate and ultimate father of the 6L6, and all that grid is magnified by the gain from [he grid came after. to th� plate, This is the "Miller Effec[,� This is a good place 10 describe the technical basics. In a tfiode electrons an: boiled offthe cathode or filament by heat. The eb:trons are attracted strongly 10 the positively-charged plate. But 10 Sel 10 it, they must pass through the con trol grid in their path. By varying the voltage on the grid, the electron stream is varied. Simple enough. Unfonun;l.Ie1y, then� lre three prob. Jems here. First, the maximum current that can flow at low plate vohages is lim ited, and this limits rhe maximum power output. Second, in order 10 gel a high maximum plate (urrenr, the �mu· (voltage: EmlyFiftin Heluhkit A-8 6L6 Amp Figure J gain) needs 10 be low, requiring a high VACUUM TUB E VALLEY 6 L 6 FOR EVER 6L6GAY,6L6GA IlIId6L6G response. h also increased gain, as the fixed voltage on the screen made the plate current less dependent on the variations of plate voltage. The resulting "tetrode" became a standard for RF amplifiers in radios, and the RCA 48 was about as good as a tctrode could be made for audio. Figure 4 -,--_. <,,'" ,,, .... [ BtH when used for amplifying audio, (ctrodes have a problem. The secondary emission can be anTacrcd [0 {he: screen grid, which lowers the plate current for low plate vohages. This is the famous lenode "kink" (Fig. 2). It is a source of distortion in audio, and representS some wasted energy as welL Because of (his, a third grid was added be[Ween (hescreen and pfate. The «suppressor� grid is wide ly spaced and is at the same voltage as (he cathode. Thus, secondary electrons which bounce ofTthe plate will be rep elled away from the screen and back to the plate. The kink disappears , and we have a «pentode". Gain and efficiency arc very high, frequency response is excellem, and distortion is lowered. Even so, the RCA engineers knew (hat RaytheOll6L6GB and GE 6L6GB (he pemode has problems. One obvious onc is that the screen and control grids and it makes triodes harder to use at high g id, because it acted as an elecnostalic r are wound with different wire spacing. frequencies. So triodes have limits on screen be[Ween the g id and plate, reduc r Some electrons will pass through the their frequency response and efficiency, ing the plate-grid capacitance. This spaces in the control grid, only to STrike when used as power amplifiers. opened up the short-wave bands, because (o be deAecled a useless direction by) (he screen allowed greater fr equency r in ELECTRON BEAM-FORMING PLATE STREAM SCREEN GRID VIRTUAL CATHODE In the 1930s the problems were difficult roget around; triodes with low capacitance were evemually designed. But at thetime, efficiencywas best Figure3 PLATE addinganother grid (Fig. impro\-edby CATHODE previouspage). This w:u <:alled a «screen" VACUUM TUB E VALLEY 6 L 6 FOREVER appeared; ham-radio opcmors found (hat it could give usable power in a transmit ter, <,vcn at shortwave frequencies, and at far lower COSl than previous tubes or the official transmitting version of the 6L6, the 807. The COSt of ublic address amplifiersWali affccu�J' by the new tube, as it was now practical 10 get 2; \Vaus wilhoul using four 2A3s or (')(pensive larger triodes like the 50 or 21 1. Only tWO 6L6s WCfC now needed, at a fraction of the COSI. 2. Types The 6L6 gave binh IQ a vast arr"y of beam tubes. The 6\'6, 25L6, and others wccc immediate d�elopmcms, which gave lower power for small radios at lower COSL The 807 was the beginning of a series of beam tubes intended for radio Lion GEe KT66ttnd Gold KT66 transmiuc:rs, some of which arc usable beyond 500 MHI. The 807 was the GB 6L6GC. Rot (Bladt Plate) 61_6GC direct anccslOr of the famous 6146 trans� ."ti5y/", ,,,;. 6L6GC 5TR mitdng tube. The major VHF push-pull tenodes of World W:.u 11, the 815 and 829, were based on the 6L6. The 6550 was a high-power audio tube based on classic beam tetrode principles. The firstAmerican television horizon tal amplifier or �sweep" tube, the 6BG6G, came OUt in 1946, and was a repackaged 6L6. It was followed by doZtns of derivatives ending Up in the mOnSter eclor TV sweep tubes of the 19705, such as the 6LQ6 and 6KG6/EL509. To this day, new mbes are being developed that are descended from the 6L6. The KT90, KT99 and KT! 00 are examples. These recent audio tubes are derived from TV sweep tubes. The original metal 6L6 was a typical a scteen-grid wire directly in that space. they wound the comrol grid and the design for RCA at (he time. Metal-shell Those electrons are wasted energy, and do screen grid with the same pitch. The tubes were popular in the 19305. They not rellch the lood. The elecnons that wires were aligned, so ver)' few electrOIl) were heavily marketed to the public who strike the screen just heat it up. A similar would strike the screen. Second, the sup· feared injuring their hands on broken interaction can happen with the screen pressor grid was replaced with a pair of glass and to radio manufacturers who, and suppressor, but it mostly involves the: Ubeam plates" on either side of the grid among other things, appreciated the f;\C! secondary electrons. And some electrons structure. This assured that the onl), elec ,hat metal tubes were less likely 10 break can pass through gaps at the tOP and bO!· trons reaching the plate were in the arell during shipping of their f2dio secs. An added feature w:lS Ihe shielding effen of tom of the grid assemhly, or strike the where the critical plate distance was right, f the metal envelope, which improved side rods o the grids. So the main elec· insuring the "virtual cathode" was effec tron beam can ha,·e a circuitous route. ti,·e. The result was extremel), high radio performance. Most of the wasted energy heats the efficiency, high linearity and lowered grid The steel envelope was more expen· screen grid, which in an eXtreme case can heating. The first production version of sive 10 manufacture and had real prob make it emit eleCtrOns, causing the tube's this was encased in a metal envelope with lems dissipating heat, so the fad was vir plate current 10 run away. a then-new o<:tal base. Thus was born tually over by 1950. The metal 6L6 and the 6L6. In England, studics on secondary its premium version, 1614, were olten emissions showed that by spacing the It was an immediate hi\. All th.: used in early jukebox amps and in many Zenith radio chassis, nOI to mention FA plate a critical distance from the screen major radio manufacturers started using ll amps. grid in a teuode, a "virtual cathode" is it in their audio Output stages, essentia y formed. [1 J (Figures 3 and 4 on previous eliminating the triodes, such as {he 45 A few maniacal radio hams found that page) Schade and his fellow ReA engi. and 2A3, and elbowing our old teerodes a metal 61.6 could be operated in a balh neers lOok this concept and perfected its like the 46 and 48, and pentodes like the implementation in several w:lYS. First, 47 and 6F6. And new applications VACUUM TUB E VAL LEY • 6 L 6 FOR EVER of transformer oil, allowing a pair 10 dissi WE350B (built byNatiollal UlIio,J) Imd MullardEL3J pale 150 waIlS for shon periods. The glass 6L6G and 6L6GX, appearing in 1937, were morc popular with the conser vative audio indusuy. The 6L6G was . �.' common in nearly all W\'V'II jukeboxes, and became nearly universal in thousands • e' W'" -_r� of PA amps right Ihrough the early Fifties. ' . .. Although {he G version had the same ra{ ings as the metal sryle, it lOok over the EL37 r market. During World W'ar 11, improvements :4 .@'· were made in (he glass envelopes, and in f-�"-, 1944, Ihe 6L6GA and 6L6GAY were .', r�· .if introduced. They had the smaller ST-14 ..::Jl':,,' �coke-bottle� envelope. In the early 1950s, the 6L6GB came Out, having a straight-sided T-l2 envelope. These all had the same maximum ratings as the original 6L6G. After 1945, an escalation in power r-.H TUllg-So15881s IlIld6L6WGB ings began. This had been prefigured in the 1938 introduction in Britain of MOV's KT66, a more powerful version of the 6L6. OEMs wanted more and more power. without resorting to transmitting tubes. In 1947, Mullard introduced the EL37. It and the KT66 were more expen sive in America than the GL6s, so the RCAfGE/Svlvania business continued as more and �ore dissipation was demanded from the tubes. The result was a group of usuper tubes," which became standard for high-power American guitar amps and some hi-" amps. In 1955, the 6550 was introduced by Tu ng-Sol. During 1958, ReA came Out with the 7027. In 1959, a five-ply combi nation metal sandwich type plate design and a different maximum rating system allowed the 6L6GC to raise the plate dissi pation from 19 to 30 watts. In the early GE 7581 and Tung-So17581 1960s, the 8417 was developed. The 5881, introduced by Tu ng-Sol in 1952, was intended as a smaller 6L6 ver sion for use in military and industrial equipment. Millions of 5881s were plugged imo servo amplifiers in aircraft such as the B-52 bomber, so this had to be a rugged and reliable tube. It was Stan dard equipmem in some home hi-fi amplifiers, such as the classic Bell, Bogen, Heathkit WM-3 and WM-4 series, Fisher 70A, Pilot AA-41 0 and many others. • Fender's early Bassman was equipped with 5881s, and this guitar amp (like many later models) is very demanding of its power tubes. 6L6Gs simply cannot be used in such amps! The 5932 was Sylvania's rugged 6L6 type. It was never used in audio equip ment and is extremely scarce. See below for more information on the 3 variations VACUUM TUB E VALLEY 6 L 6 FOREVER Sy/vtmill 5932s (singk p/nu, singl� PMU wlhoks, dUIIIplnu) that �STR," long afm the 1988 shutdown of the Sylvania tube factOry, is a standard term used to describe 6L6GCs with this large cylindrical envelope. GE even intro· duced it's own version, and both had numerous guitar amps designed around them. I once repaired a guitar amp made by AcouStic, circa 1979. It had four GLGGC-STRs. and PUt 750 voltS on them. The owners of this model don't realize that they ha'·e a dangerous beaSt there. Unfortunately, many such amps continue to be used, although the STR tubes arc no I�nger being made and are gwing expen· Sll'e. Ikuuse of the chaos of 6L6 types and the often· brutal conditions they endure in music amps, testing becomes even more important. The problem with some types is usually their design limitations. not on this tube. General Elecuic tried to There were so many variations of Ihis design Aaws. Older tubes often had sur· make a super-6L6 in the late: Fifties, and form Ihal don't have space {Q list them in face treatmentS on their mia insulators the result was (he 758!. You can easily this magazine. I could go into the 6AR6, which reduced manufacturing COSts, whilc rccogni'a: a real GE 7581 by its pinkish or the Bendix Red Bank 6384 (to be cov allowing some leakage current to reach flesh-colore Table I: As I said. the major applications of As with previous tube: tests in past EscaJalioD OF 6L6 these tubes were in PA amplifiers and issues of VIV, I used a special single· radio OUlputS. jukeboxes. and some early ended teSt amp 10 examine the distortion Ratings Oyer The Years hi·fi amps. But the fUlUre.and 10ngevilY characteristics of a large cross- scclion of Plau' I'lal� SCf<;:<;:11 of the GL6 were assured when Leo Fender old 6LG types, as well as.a few current-pro put them in his large guitar amps, staT( duction items. The driver was a GEM7 WatTS Vollagl:' Voltage ing with !he Dual Professional in 1947. and the Outpul load was a One Electron 19W V 6L6/G/GAlG B 360V 270 Fender's large amps of the late J 950s, UBT·I SE transformer with the 8-ohm tts! KT66 (19405-on) 25 W 500 V 400 V including the Showman, Bandmaster. load connected to the 4·ohm lap. thus pre EL37 (1947) '5W 800 V 800 V Bassman. Pro. and Twin models, becalll� senting 3200 ohms to the tube's plate. This Ihe essence of American rock. Indeed. the lest has been most revealing in the past, 5932 (1950) 21W 400V 300 V 1959 Bassman and 1960Twin are among and the 6L6s were even more unexpected 5881 (1951) 23 W 360 V 270V the most copied electronic adgets in his· � in their behavior. As in the past, diStor 6LGGC (1959) 30W 500 V 450 V tory, with a variety of new boutlque� tion is almost a!! second-harmonic and was 7027 (1958) 35W 600 V 500 V manufacmrers producing their own ver· measured at I watt into an 8-ohm load. 7581 (1959) 30W 500 V 450 V sions. If you include the GV6-powered E.ach tube was biased to 50 miliiamps, a Deluxe models in that short list, Ihen the typical value for 6L6s, then lested. All th� 7581A (1960) 35W 500 V 450 V old Fender designs are the undisputed types were run at 300 volts triooe connec [h >ho>uld be: "",cd ,h., ,ubc:.in",.Ju«J .r,�, standards. tion. then types thal were rated to aCCept 1957 uot ,h. -(X,iS',.C VACUUM TUBE VALLEY • 6 L 6 FOREVER RussiAn 6P3S, Sovtek 5881 and ROt 7027 the other hand, for guitar the tubes pre ferred are usually the short CE GLGCC, the "STR" GLGGCs made by Sylvania and CE, and the various 58815, 6L6WCBs, 758lAs and 7027As. In this case, distortion is OK (and sometimes deliberately sought by the user) but phys ical ruggedness is more critical. This is why the metal types and the old 6L6C, CA, and GB are less soughl-after. The laner are in demand, but mostly by radio collectors and juke-box owners who want to use original tubes. For applications like these, where [he plate vohage is below 350 volts, the current Russian �P3S works JUSt fine and is very inexp"n s!ve. Mctal 6L6£ (induding the IGI4) are loll' in distortion, but tend to be micro phonic and can have dissipation prob lems. A power tube with a melal enve lope really should be cooled by forced air or attached 10 a heat-sink, neither of which is practical in typical audio amps. Many tubes {hat appear on the 300V The more extreme collectors of Mclntosh lisl are not on the 500V list. This is hi-fi equipment usually insist rhar lheir 6L6 Typeswith Multiple Samples: because thuse particular !Ubes are NOT MC-30s be equipped with lGl4s, thc I. Triode 300V a.. er age di�tortion rated by their manufacturers for operation original equipment in these amps. 1614 mcral RCA _61% 4 $:IIIIplrs at 500 volts on the plate. This includes For true obscuriry, the Sylvania 5932 6L6 mml RCA .62 4 the metal 6LGs and lGl4s, the 6LGG, is wOf!h looking at. It is a special super KT66 MOV .63 4 GA, GB, and the Russian 6P3S, which is rugged 6L6 replacement for military GP3S Ru.\.Sian .64 12 often sold as a GLGGC even though it is equipment. The 5932 came in three ver 6L6GC Sylvania dlOn .72 4 not intended for more than 400V on the sions; tWO had a conventional single Struc EO? Mullard .78 4 plate. (A true GC should be rated for ture. The other version is unique-it has 5881 $m'lck Russia 85 4 500V.) We respect the imemions of rhe a pair of smaller oval structures connected 6L6G RCA .85 l original manufacturers. So, toO, should in parallel. There is an underground fol 5932 SyIJAN .91 2 users stick to the published ratings. [ have lowing in the guitar world for the 2-plate 6L6GC China .93 2 Hied to put 500V on the older types and 5932, and the prices charged for it rel1ect 6L6WGB Pllilip! shot! .93 8 on 6P3Ss, and [hey usually stan to creak the demand (high). Its distortion and 6L6WGB GE Canada .96 9 (and, sometimes, Hy to self-destruct due power Output wert' only average, similar 7027A RCA .97 4 to grid emission or leabge currents). I 10 Tung-SoI 5881s. 588116L6WGB TungSol .98 18 definitely do not recommend these types for guitar amps, which often have plate 7581A Philip! 1985 1.06 2 All of the tubes listed here are pin voltages of 450V or more. 7581A GE pink base L06 2 compatible replacements for any GL6 6L6GC GE ,hon 1.18 l The peak-power lests arc nOI listed type, except the 7027 and 7027A. Socket. 2. Pentode 500V (scre.,n 300V) average here, but we will summarize: it was must be rewired 10 use them in place of distortion revealed that the MOV KTGG, Mullard GL6s. A good tube-amp technician can KT66 MOV .88% 4 sampb EL37, Sylvania GC and the rare 350B (a do this at a reasonable price. Because of £L37 Mullard .91 4 Western Electric type) arc superior to the manic market for NOS types that can 6L6GC Sylv.mia ihof{ .95 3 other GLG types in peak OUtput. If the substitute for 6L6GC, 7027s have become 5881 Sovlck 1989 .97 4 application demands maximum peak OU t very scarce. There were few audio amps 6L6WCB GE Canada 1.07 6 put (and money is no object), these tubes that used them as original equipment. 5881/6L6WGB TungSol 1.08 17 arc best. Bc prepared to pay more than They are very lOugh and arc popular in 6L6GC China 1.08 2 $150 for each KTG6, EL37 or 350B. Fender amps that have been rewired 6L6WGB PhiUSr' short 1.12 \0 NOS usually brings such prices, but good appropriately. Purists tend to scoff, as 7027A RCA L\4 4 used tubes are acceptable. Make sure 7027s are quite different from GLGGCs 6L6GC S)'lvaniaSTR 1.16 2 your NOS dealer warramies that the used and the like; but they do work fine with 5932 Sri JA!'\' 1.16 2 tube is healthy! JUSt a socket rewiring and rebiasing. 7581A GE pink base 1.I9 2 The 6L6 is not often seen in high-end 7581A Philip> 1985 1.22 2 1/1 using this list, keep in mind that hi-fi amplifiers. There are some old amps 6L6GC GE short 1.25 2 the needs of hi-fi and guitar amplification do not necessarily match. It is typical for our there, however, and they can be kept hi-fi users to prefer !Ubes from the top of going with rhe Russian 5881. It is [he list; the KTGG and EL37 are especially unpopular in guitar amps, even though sought- after, and the list reflects this. On it's rugged and inexpensive. Guitarists VACUUM TUBE VALLEY 6 L 6 FOREVER The British Connection In England in 1931.J.H. Owens Hllrries discovered that if the elecrron flow in a tetrode was confined to beams, and that the distance from scr�en grid to plate WllS kept at a critk21 distance, sec ondary emission from the plate would be suppressed, JUSt as in a pentode [1,3]. This discoverr enabled the British General Electric Co. (GEC, unrelatcd to the Americ:an General Electric) to bring out a sensitive, high-power OUtpUt tube without infringing on the pentode patenrs held by Philips and Mullard. M.O. Valve, a division ofGEC, then c:ame. OUl with a series of beam tetrodes, with their most famous being the KT66. KT stood for "Kinkless Te trodc� - since it eliminated Ihe kink in the transfer curve that happened with regular t("[rodes.The KT66 was meant to be a SylVflll;1l 5881/6L6WCB'/lid RC4 5881s plug-in replacement for the 6L6, but had superior characteristics. h was intro duced in 1937. These and other M.O. Icnd 10 dislike Russian 5881s because than 400V. During test at 500V pen Valve tubes were marketed in AmeriCl they sound �b!and.H A shame, as rhey're tode, they creaked and groaned alarming under the "Genelex� name. good hi-fi tubes but rarely used for Iba!. ly. Note that their distortion was much Mosl corucmporary high-end designers higher than in the Russian ones. Due to the head star! the British had have tended 10 slay away from using Obviously these tubes were made with in developing component-type high 6L6/S8Sl s in their amp designs. The Russian tooling, but are much poorer fidelity systcms, the transfet of British Golden Tube Audio St..-40 single-ended quality. There is a new "Coke-botrle� RADAR technology to American during amp. Mesa Baron and various VrL push shaped 6L6 ftom Shuguang, with a WW 11, and the common language, pull amplifiers are among Ihe few con brown base and optional blue 11ass; il is Americans in the late 19405 looked 10 temporary high-end amps Ihat use the 100 new 10 appear here and wi I b� England for ideas in hi-fi design. bUllOn-base Russian 5881. reviewed later. Williamson's seminal Wireless World articles gave British hi-fi a tremendous I (:oncluCled easual lislcning testS al All of the NOS tubes are out of pro boost in Americ:a. The marketing effortS the vrv office; they tended 10 back up duction, leaving only the Russian 6P3S, of the British Industries Corp (B.l.C) the distortion tests above. The old 5881, and the Chinese types. The brought the best of British hi-fi compo GL6GCs tended toward a warm, "roman Russian tubes are old Soviel commercial nents to America during the 19505. The lic� sound with greater �darkness· and and military types, nOt originally intend· net result of this was the inclusion of much mon: distorted, fatbass. The meral ed for expon. $vetlana is going to intro "foreign" tubes, such as the KT66, Iypes and Russian 5881s were more �dry" duce a new 5881 of its own soon, and wc t-.'T88, EL34, GZ34, etc. into American and dean, as wefe 6L6Gs and Sylvania will repon on it in a future issue of VfV. hi-fi and evcn guitar amp designs. GG. The 6P3S has a slightly welter - uch. Ed. sound than the Russian 5881, but the 4.0uII"0 same kind of clarity. Old 5SSls were It is cstimated that more than 2 mil· mostly made by Tung-Sol, and sounded lion lube guitar amps exist in the world 6L6GC-"STR" which may be produced warm, slightly nasal, with good bass. The toda),. Of that number, probably more in Clllifornia soon, and the 6L6 looks KT66s and E137s were outstanding hi·fi than 40% use push-pull 6L6s. To claim good for another 60 years. wbes, more like triodes in charaCter and that this markct will soon dry up and be References: very detailed. replaced by transistors is simply pr�l'arica. tive. Although no 6L6 rype is b�ing pro· 1 - Harries, YrolldaryElutrol/ RadulflolI, Two examples of the -skinny� duced in Am�rica or Europe at the pre Electronics, &pl. 1944. Shuguang GLGGC are listed here. These Sent time, there are a few po pular ones 2 _ Sch�de, O.H. Be�m I'o er Tubes. PrO\.. of look remarkably like the Russian GP3$, ..... from Russia and China which own the the IRE, Feb. 1938. but are slightly different. The Chinese market. The Shuguang types. including a 3 _ H�rries, British pU�nt� 380,429 and version has four square holes in its top new 6L6GC with a blue glas5 envelo�, 385,968,1931. and Wireless Eng., \'01. IJ, mica. spacer, rather than the tWO in the are consiStent scllers; and although ther pp. 190-199, April 1936. Russian mbe's spacer. Chinese 6L6s also are very clcan-sounding tubes, the look less well-made and use the same ugly Russian-made 5881s are $oldano's brown refractory cement to hold bases on favorites and are used widely. They will TJNmlnto Kml u«hfrom Om.M, Gllifomia rhat is seen in other Chinese octal tubes. likely be available for years, if not forhis cur-awa) i/J1l1/TlltjOlt (Ifa 6L6 on These, like (he 6P3S, arc not really decadcs, to comc. Add in the soon· to pagr 3. GL6GCs and should nor be used at more come $vetlana 5881 and a rumored VACUUM TUB E VALLEY .. V T V LIS TEN S T 0 THE 6 L 6 6L6 Listening Impressions Hi Fi - by Charlie Kitdeson Guitar - by Te rry Buddingh This wmparison will he in two parts. • I will gi\-c listening impressions of the 6L6 in hi fi applications using John Arwood's SE amp with all cube regula tion, yariable plate currem and a Ta ngo SE transformer. John wrOTe an article on this amplifier that was published in the March 1996 M] mag:nine. Te rry Buddingh, cube amp guru for GU;lijr P14yer Magazille uses both an original 1959 Fender Bassman and a 1963 Fende.r Twin Reverb for his listening impressions. 6L6 for Hi Fi rolled offat the top. Mids nOl very impressions of 6L6 types in vintage All of the tubes wcre se! at 50 ml detailed and a noticeable bump in rhe Fender guitar amps: plate current except for the KT66, EL37 higher mids. Overall, a softer, vintage and \'(1E3508 which were set at GO ma. type sound. Sovtek 5881-Thi$ tube has a lean, colorless midrange and a slicey tOp. Tu ng-Sol 5SSI-This tube has a RCA 6L6 (metal)-Very dt:tailt:d, rich Philips/Sylvania 7581-A (Ube with good punchy midrange, however the highs mids with a noticeable mid-bass resonant head-room and tight bass. The loudest were harsh and there was no major depth peak, a good audiophile tube if plate voh and deanest of the 6L6 types. Chinese in rhe bass. Sovtek S881-Good detail, age is kept to a max of 360 volts. 616-Not super musical, harsh treble and bur somewhat dry sounding. Fine tonal WE350B-Sweet upper-end derail with can't handle high B+ plate voltages. balance and tight bass wirh good damp· lots of headroom. Very balanced with Tung-Sol 5881-Definitely a tube with ing. Nor as musical as some of the vin tight bass. Three dimensional and live rhat grindy twang that sounds great in tage tubes, bur may please the detail ori sounding. Easily the most musical tube early Fenders amps. ented audiophile. The best 6L6 type for of the test. Mullard EL37-Warm and hi fi currently being manufactured. round sounding with lots of detail and Sylvania 5881/6LGWGB A good Sylvania 5932-The twin plate version of depth. Not a hint or harshness, very vintage sounding 6L6 with smooth, 6L6GC rhis (Ube was wdl balanced with nice much like a Iriode. Not quite as lush in creamy mids. RCA (black highs. It was relaxed sounding and not the midronge as the WE350B. GEe plate)-This tube from the late Fifries and harsh. The single large plate version with KT66 (early smoke glass)-Lush upper early Sixties is especially rich and full n ing T e S v i STR 6L6GC holes seemed [0 have notable diS[OT(ion mids, but somewhat bright highs. sou d . h yl an a in the mids and highs. The large plat'e Extremely smooth, but clean and This tube has a tight, firm bottom and a version wirhoul holes again had a bal detailed. Bass was no! as deep as the hard, stiff midrange and top. Mullard anced sound with lots of midrange and WE350B. Excellent vintage sounding EL37-E137s are incredible - sonically, they're between a Mullard EL34 and a high frequency information. It was very tube. Gold Lion KT66 (clear glass) pleasing, with fu ll sound. Detailed high-end, a sensitive tube, but GE 6L6GC - Strong and punchy with the midrange sounded a bit congested good richness and complexity in the RCA 6L6G-A very laid-back, round and the bass was not super-deep. midrange. Genalex KT66-The KT66 sound with a smooth low end sweet highs has the most incredibly refined sense of and not roo forward sounding. Sylvania midrange presentation and detail. The 616GA-Good-deep bass, rich low-mids, bass can be somewhat loose. GE nice balance, smooth and easy [O lislen 6L6GB-Nice and smooth, a good vin [0. GE 6L6GC-Refined and balanced, tage-sounding tube for guitar. Cannot nOI hyper-detailed, a semi-punchy vin safely handle much over 360 volts on the rage-type sound. RCA 6L6GC plate, however. Blackplate-Heavier bass, but not as bal anced as the GE version. Sligh tly thinner sounding in the mids and highs. Terry's Recommendations: �For • blues and rock one of my favorite tubes is Sylvania STR387(6L6GC)-Strong bass, the RCA 6L6GC, "Black plate" for its thinner upper-mids and highs than the rich and smooth sonic presentation. For GE 6L6GC. GE 6L6 GB -A fatter, vin a loud and clear sound, try the tage sound with more depth in the bass Philips 7581, easily the cleanest tube of the lot." and mids. Tung Sol 7581-1..ots of meat 6L6 Ty pes for Guitar Amps in the upper-mids, bur somewhar harsher Terry Buddingh, from G,lilllr Player 6 S highs. USSR P3 (6L6GC)-This tube Magazine and a contributor to vrv lacks bass depth and the highs are slightly from rhe guitar amp side, gave us his VACUUM TUBE VALLEY • = WHY 8 8 T 0 1 0 8 1 tional bodies. The seven Fee commis Why 88 to 1081 sioners as well as rhe chairman of the Fee were political appointees. The History of Early FM Radio In late 1944, Fr.mklin Rooseveh by John Atwood (FOR) had won an unprecedented 4th term. Among the political appointments made after the election, the publici t directOr of the Democratic Nationar OUT day-to-day environment was once Committee, Paul Porter, was rewarded by defined by objects: moulHai ns, buildings, being made chairman of the Fee. Paul roads, houses, food, and books. Poner was a lawyer, and had never been Nowadays, technological standards define invoked with radio or broadcasting until more of our environment: SO or 60 HI his appointment. power, Public Broadcasting Channels, speed limits, c-mai] addresses. Onc of the The Secret Hearing5 uxhnological landmarks of our cm'iron With the end of th(:' war in sighl, th<, � men! is (he: exis« nce of radio frequency Fee began preparing the new frequency bands - and tbe fo cus of this article, the simply receiving a noise-free signal from allocations. Interested p:mies were given 88 to 108 MHz FM broadcasting band another station and rebroadcasting it, a chances to explain their needs and desires used in North America and in many radio network could a\'oid the high COStS to ,he Fee in public hearings before the 10 other pans of rhe world. Why 88 I08� and (at that time) limited fideliry of commissioners. However, on March 12 The: answer became clear arrer going AT&T's leased lines. By the beginning of and 13, 1945, secrel (non-public) hear through a Slack of post-war FM-TVm ag America's involvement in World \V!ar 11, ings were held to discuss the allocation of azines, edired by olle of the pioneers of Ihere were 115 FM srntions on Ihe air, all FM broadcasting frequencies. Ap arendy, high -fidelity, Milton B. Sleeper. Slcc ' r r between 42 and 50 mc. Kenneth NOTIon, the FeC's chie engi was an ardenc supporter of FM in al neer, gave testimony that propagation at forms, �nd while his mag;'l1.ine clearly is FM's rise was nOI viewed positively by high frequencies was bener for FM slamed IOwards FM, he presems enough the dominant economic fo rce in the radio broadcasting than (he current 42 - 50 mc. source material (Fee announcements, world al Ihe ti�e; AM commercial • band. [2J ICHers from the anti-FM side, etc.) that a broadcasters. FM broadcasters tended to fairly clear picture of (he politics of POSt be forward-thinking innovators, and evell We don't know all the details of the war FM emerges. This article will fo cus though AM broadcas ting was only 20 hearings, but the net result was Ihat when in on the events from 1945 to 1948; years old al Ihe time, if had become an frequency allocations for all services however, the hislOry, personalities, and entrenched big business. The telephone above 30 mc. were announced on May confl ictS surrounding early FM broadcast monopoly, AT&T, saw a loss of leascd 25, 1945, no decision was reached fo r ing are fascinating, and deserve an in line revenue. And at the biggest radio FM broadcasling. Instead, three altema depth treatment elsewhere. conlpany, RCA, Sarnoff, formerly li\'es were announced. AI this point Armstrong's supponcr, had turned against Mihon Sleeper explains it hest: A Little FM History Armstrong, and was trying to neulralize "Manufilclurcrs prole�ltd vigorously The concept of frequency-modulation his patents. While rhe AM broadcasters againsl the delay in assigning FM for radio communications goes back to were simply greedy and short-sighted, Broadcasl requencits. Television RCAa ctually saw the benefit of FM, but f the 1920s. Some misguided studies by BroadcasteT3 Asso<;iarion, FM Bell Labs had convinced mosr communi worked hard 10 develop circuits outside BroadnstCT3, Inc., and rhe Pioneer I:M cations engineers that FM was no better of Armsnong's patents. ReA actually Manufacrurers Conference prompd)' than AM. However, Major Edwin H. pushed to make the sound channel of the (»$$I'd resolutions ailing upon the FCe Armstrong was a firm believer in the NTSC teb'ision speci fication FM, JUSt to make the No. I Alternath-e effcctive at superiority of FM over AM , and on Nov. before it was adopted in late 1941. But once, giving FM 48 1068 me., wirh 68 10 5, 1935 conduCled a dramatic demonstra Samoff wanted FM on his own terms, 74 and 78 (0 J08 me. for television. tion before the InstitUle of Radio nOt Armsuong's. �The announcement of the three alter Engineers in New Broadcasting Yo rk. the FCCI wasco :te The Power of the: Fee native plans [by mpa from Yonkers to the Empire State nied by an e�planalion which srated. in Building, the New Yo rk Section of Ihe During the war, AM and FM broad parI, Ihar �equipmem consider-lIionl IRE was the firn 10 experience dear, stat caSting continued, bUI few new station should not be complicated by mO"ing to ic-free radio transmission. Armstrong permitS werc granted. By 1944, it was higher frequencies unltss ir is dear Ihat received permission to regularly broadcast clear that all (he frequency allocations Ihere will be definite advantagcs fro m a at 43.1 mc 11 J (We will use Megacycles would be rc:evaluated - bOlh because of propagation standpoint." instead of MegaHertz in this article, just all sortS of new military radio uses, and ·However, under preil.ure from Ihe AM to keep the flavor of the time.) Soon FM beau� of the expected boom in televi broadcasting induSlf)" the final choice of stations were being set up in both major sion and radio broadcasting. The Federal the No. 3 Alternalive. movi ng FM (0 88 cities and in rural areas in the 42 to 50 Communications Commission, fo rmed 10 108 me. . was announced on June 27, mc. band. High power stations demon by the 1934 Communications Act, estab 1945. This was done in the filceof slate strated that dear, noise-free signals could lished all radio frequency allocalions and menu from manufactureT$ aplaining that propagate over a bigger area than daytime ,,!ulations. Given America's t«hnologi neither designs nor tubes were available AM broadcasting. The Yankee Network ca and political dominance at the time, for rcceivcl1 and transmim:rs on 88 10 108 in the north-east V.S. showed rhat by there was linle input from any interna- mc. Moreovcr, as was disclosed subse quem I)" the Nono n tcs timony supporting VACUUM TUB E VALLEY la WHY 8 8 T 0 I 0 8 ? "' .•.featuring the Genuine Armstrong " Circuit in Both the 50 and 100 Megacycle Bands The Public Is Demanding FM And Up! .. And Zenith Has The Answer Or ffic .. I"�",,, h ,,·ill �b lJy be vo:ry di ult 1<1 !cll a,,)' ,aJi" (�"I't ill th price ..� .. f:\1. V brackets or portable.) ,..hid, ,I, "ut inooFp"'l1l L· II'l" Iou I llg ONLY ZENITH HAS THIS! �"g"i.ed the uniw"""l apl>o:al or lhi� IIe"- �il1d of �Iali�.rr�.." Irue fldelil)' • Go.vl., ...."'._ •• FM 0. ....h T�"I•• brOlldcasling a.� devdop<-..t �y Major Eel.. -;n 11. Ann.l.oIIIl_ Tu rn,..,1 it. h.d. i.enilh' engilll"tn h�n' p,·rfcclc�l l ..·".J"",,1 Armslrolll!r�r ill table m.... ld ...... w.. ,.. •• T� ... * ...1..... fM ...... Iv.. ... Te'" do:o; .. 10 si ",IS ig 1 to HI'I'" I the rna"�, ""lurne market . .... "dl i" the fi",;,1 ""m "", ... "ollsole combi"QI;"n� all "'illl 7...,,,;lh'8 palellkd built·;Il light_I in" • ",", 1... ,•• 10, DIa' a"l�nna. Thai is why 7.... II;lh is ",c"OS";'''''] by broadcasters. dc..ucr;; and Ih" * ,.. ",_'k, " ,...... , • Co .."" .. Cha .... l,ulJic as the oUl�la",li"g "'31l"facturt'r ... r F\( rece;"ers. * ...,Io.l. Wwv ... o.,. .. * 5... • • ,5., ...1 •• C�,." Zenith " Building A Mo" FM Audience: ", of ali lh" FM C,\U;pl'.. .I Ta !>l mood �<:I� pr...JlIcui ...... ZENITH RADIO CORPORATION CHICAGO 39, ILLINOIS ... the use of higher frequen(ies had been nouncement that "The Commission is "Now th.. truth was that Chairman proved, at th� $ecr�t Hearing on March informed that IO-kilovvau transminer, Porter had not been informed by any 12 and 13, 1945, 10 be grossly in error." will be available for [he new band: and authoritaci"e source that " IO-kilowau [hat «[he Commission might vcr)' wdl uansminers will h< immediately availabk �ConfrOnled with a complete shift of lake .he position that it wa� necessary [0 for the new band." That srat�me.u was FM frequencies, the Pioneer FM put an end immediately (0 all F"'I Irans nothing more than a lawyer's answer {O ManufaCTurers Conference, meeting on missions in the old band in order 10 pro juStifyhis position. There was nOt a word July 6th, announced that as a service tu teC! [he public from an unnecessary of truth in it, and Ihe IUvlA [Radio radio listeners, they would provide 2-band expense and [0 insure [hat [he change-o,·tr Manufacturer's Association] would nOt FM tuning. Thereupon, Chairman POrler to (:M's neW and permanent home should have IO-kw. equipment for FM for iO {O a steprM imo a situ tion over whi(h he had nOt be dela)'ed.�" 12 months: [3] 110 jurisdiction whatever with the pro- VACUUM TUB E VALLEY WHY 8 8 T 0 I 0 8 ? Nil turned OUI, the very firST new Zenith's Request For Two Band peaked in 1948 at 132,500 per month. hand IQ kw FM transmiltcr Came on the Coverage Production dropped to an average of ai r in latc August, 1946, over a yellT aftcr On January 2, 1946, unith Radio 32,000 per month in 1952. 191 FM's Porter's claim that they would � "imme Corp. filed a petition with the FCC to replacement of AM clearly didn't happen. diately" �vailable. This station, by the allow broadcasting on a limited section of However, the numbers above do not way. was Armstrong's Alpine, New Jersey the old 42 to SO me. band, rimarily ro include separate FM tuners, and the station, W2XEA. Another poStscript: In p allow better FM coverage of rural areas. growth of the hi-fi industry kept the FM May. 1945, the: Fee requc:stcd Zenith By this time the results of Z�nitb's dual market alive. It wasn't until the laIC 1960� Radio 10 ,ondue! teStS comparing broad band tests had come in, showing a 40% that H.,I would become a broadcasting castin on the 50 and 100 me. bands in g loss in area covered (for the same pOwer marker comparable with AM. Dec:rfic ld, Illinois. On December 28, level) for the 100 me. band. The FCC 1945, Zenith reponed to the Fee that One of the good things that came OUt scheduled he:lrings on Jan 18. {61 "while rendering good service 10 a limited of the move to the new FM band was an Aft�rwards, on Jan. 23, the FCe reaf area, [the new hand] will satisfactorily enlargement of the band, and the alloca firmed its decision to keep a single FM cover only 40% of the: area which could tion of 20% of tbe band to public and band at 88 to 108 me., without issuing be covered by a similar transmitter of community broadcasting. Enlarging the the CUStomary explanation of its decision idemical power in the 50 me. hand. Thi� old 40 mc. band would require conver until March 5. Commenting on the fa ct means that the majority of rurn! popula sion ofTY channel 2, to FM. CBS, that the FCC did not admit the technical tion of the United SI'ales would be whose New Yo rk TV station was on chan errors (Nonon's flawed estimates of 100 deprived of smile-free FM service if FM nel 2, would have surely objected. Tbe mc. propagation), Major ArmsHong com were confined exelusively w [00 mc.� 141 college and community radio stations mented: These findings came seven months tOO that exist today from 88.1 to 92.9 MHz late. Comfoversies reg.. ding the laws of n�ture provide some of the few alternatives to are never dosed umil the facts come out. The the commercial "wasteland." The Single-Market Plan only "'lily the fiacu in this situation can be sup Other countries took tbe lead froll1 While not directly relau:d to (hI! �hift pressed is by shulting down the present 40- of FM broadcasting to the �ncw band�, the United States in moving their FM megacycle nadons before comparative IXrfor. broadcasting band (if they had onc) 10 another thorn in the side of FM btoad mancc of me [WO bands can be observtd in the 100 me. region. Most countries had casters was the Msingle_market- plan. Te sts actual practice by engineers and the public government-run broadC:.J.sting, with very by Msuper_power" HI,1 stations in the early alike. 171 1940s showed that FM could deliver 24- few channels, so their frequency nec:ds 10 IOU hour-a-day quality service over a surpris were less. Europe generally uses 88 In anticipiltioll of acceptance of the ingly large area. The AM broadcasters MI·h, while Japan uses 79 10 88 MH'L dual-band proposal, Zenith's new post had limited ground-wave coverage by day, (which makes you wonder why the war radios were dual-band models - cov but interference from far-away stations on Japanese import Marann lOBs!). ering bOth the SO and 100 mc bands. the same frequency at night. These ranged from table radios to con It is interesting to sec: how the politi. To ostensibly equalize the coverage of soles. However, other manufacmrers wen: cal backroom dealings during a time AM and FM station, Paul W. Kesten, the not as optimistic as Zenith, and didn't when VHF frequency allOC:.J.tions wer� in vice-chairman of the board at CBS (one offer the low-band option on their first flux shaped today's broadcasting land post-war FM sets. of the two big AM radio networks of the scape. Similar things are taking place time) proposed w the FCC the MSingle_ today regarding HDTY and digital radio Postmortem Market Plan.� In this plan, FM stations standards. It would be interesting to would be limited to an effective radiated In February, 1946, Fee chairman think how things would be if Armsuong power of 20 kw in metropolitan areas, Paul POrter was il�pointed w the had his way. with the goal to limit effective co\'erage Democratic partys board of strategy. He Rc:fc:rencu: to a 35-mile radius, or thus a Msingle mar was replaced by Charles R. Denny. Jr. as ket� from the advertising point ofv iew, an acting chairman. Like Poner, he waS a (1) - "Empire Uflh� A,,·, Tom l"wL>, pp. allowing AM and FM stations to compete lav"yer, but unlike Porter, had risen 266-267. on a similar coverage area. Despite through the ranks at the FCC since join (2) - FM & Tc:le,ision, March, 1946;Th� protest from FM broadcasters, the single ing it in OCI. 1942. Denny's track record Radio Industry Nuds the Fee's Hdp, market plan was effectively implememed as chairman of the FCC was more even �'liIton S[eeIXr. p. 23. when the detailed FM frequency alloca handed than Porter's but the FM alloca tions were made. wbich remain basically tion change could nOt be undone. (3) - Ibid. in effect today. (41 - FM & Te le"ision, Jan. 1946, p. 70. The change in bands COSt the FM At the same time the AM broadcast industry an estimated one year delay in [5] - FM & Tebision, Feb. 1946, p. 4. interests were pushing for the single-mar ramping up production of both transmit� [61 - FM & Television, Jan. 1946, pA. ket plan, they were trying to get AM ters and receivers after the war. There nill FM & li: levision, ApriL 1946, -Notes channel assignments shifted to allow 50 was a lot of interest in FM though, even 171 - FM Frequencies: kw McJear_channel� stations with no inter by AM station owners. By April, 1946, on p. 52. ference. As an example, WOR in New there were 834 applications for FM Sta [8] - FM & 'Ii:bision, M3)', 1946, "Progr"ss York was advertising that "If a sponsor tions filed, almost equal to the number uf of I:M Broadcasting; Milton Sleeper, p. 21 uses WOR, it's a sign that his rogram AM stations on the air. 67.2% of these r {91 - FM-TV, Da::. 1952, p. 4. will be heard in 16 of AmeriC:.J.S greatest were by AM station owners. [8) cities of more than 100,000 each." [51 So much for a single-market! Average monthly FM set produClion VACUUM TUB E VALLEY .. HARMAN�KARDON CITATION I AND I I Golden Age of Stereo Hegeman and fe atured push-pull 7027As melll reviews of the I and the 11 were in generating 50 warts per channel continu the January and February 1960 Audio Harman-Kardon Citation I, 11 ous. H.H. Scon came into the fra), with and th.e January 1960 Elech'ol/ics Wo rld their powerful LK-150 - 65 watt per magazInes. By Chaclie Kittleson channel amplifier ki t using pentode-con nected Tung-Sol 6550s and huge, in De5ign Considerations house wound OUtpUt transformers. Hegeman's approach to designing the In 1960, the missile age was in full Finally, Mclntosh unveiled their leg Citation line was from a professional glory and the Golden Age of hi-fi Stereo endary MC275, a ISO wan chrome stereo recording engineers perspective. \'I(lhcn was nearing its peak. Production of vacu powerhouse that is still a demand item you listen to recorded music fur a living, um tubes and related equipment was at and StatuS symbol in today's crowded listener fatigue becomes a major concern. its all-time high. Also, this was rhe era of audio amplifier market. Clearly, the race Hegeman felt that disrortion and fre Popular Electroni(s and Popular for high power amplification was on! quency response were main faCTOrs in Mechanics. American males enjoyed amplifier design and superior perfor hands-on craftsmanship and building mance. He believed lower distonion, their own electronic equipment and rools. wide bandwidth and multiple fe edback The electronic kit business was :1.{ near loops were essential for realism and to record levels and the transistor was still reduce listener fatigue. The amplifier an oddity used by the telephone company mUSt have minimal distortion to reduce and the government. the overall distortion generated fr om the cutting head, cartridge and speakers. JUSt as the competition for more "Disrortion," he said, "is a deviation from horsepower was on in Detroit in the early Ihe original. It includes harmonic, tran Sixties, the race for morc watts was run sient and intermodulation distortion ning at the local hi-fi shop. With the components as well as phase response, advent of inefficient speakers like the AR- restricted dynamic range and restricted 3 a<.:Oustic suspension speaker in 1959 diSlribution patterns from microphones and Ihe larger, conccn hall speakers like and musical instrumenlS."' I the B-310 BO'I.ak Concert Grand (which Ktually came uut in 1951), more wallS Frequency response of the amplifica were needed for more realism. In the The Citation Line is Born tion system was another major design pOSt-war mono era, 10 to 30 watts was Harman-Kardon had been in {h.: consideration. The musical response more than adequate for the popular, large audio business since the post-war era, but bandwidth must extend considerably horn-rype speakers (read: Altec, JBL, now was encountering much more com beyond the hearing characteristics of Iht Klipsch, Tannoy, etc) with ! 2 or 15 inch petition from Fisher, Mdntosh, Marantz, human ear in order to provide satisfactory woofers and <.:Ompression-type horn high H.H. Scon and many others. Most of reproduction. Thus, the concept of frequency drivers. On many of these sys the equipment sold by HK previous to "wide band" amplification was fu rrher tems, a twO watt triode amp is more than the Citation line was inregrated mid-fi developed. Hegeman felt that amplifier enough to drive you out of the room with amps and receivcrs, nothing really special performance below the 20 cycle range is volume. However, inefficientspeakers compared to the Fisher and Mdntosh I'ery important to a tight and clearly like the AR-3 needed at least 35 to 40 equipment slarring TO appear. A decision defined low end. Conversely, an amplifi watts to geT any volume. Even the was made by HK management in 1959 TO er which has a frequency response beyond fa mous KLH Model Nine Elecrrostats start a separate, high quality line of audio 100,000 cycles without evidence of ring needed at least 40 wans continuous for components for the discerning audio ing or instability when hooked to a reac any volume. This inefficiency trend still phile. The line would be available either tive load can offer clean, transparent tone continues today with most speakers being as a ki t or fully assembled and tested. in the higher frequencies with outstand no more efficient than 87-91 dba one Stewart Hegeman, a well-known record ing instrument separation. meter at one wau. But that is another ing and audio engineer and designer of A New Ap proach to Feedback issue 10 be covered at a later date. the time was brought in as Director of Engineering for the Citation Division in [n the Fifties, the lLse of fe edbKk ill The Competition 1959. During the same general time amplifiers was control'ersial ill some About the same time, a number of frame, Hegeman also designed the designs. Ty pical amps used a "single hi-fi manufacturers lOok on the chaJJengt: Lafayette KT-550A amplifier and KT- loop" fe edback circuit from the voice coil to develop and market tube stereo "super 600A preamp. Terminals to the cathode of the input power" amplifiers in kir and/or assembled tube to smooth the frequency response fo rm. Acrosound developed rhe UL-120, Throughout that year, lots of late and lower distortion. This approach lim a 120 watt stereo power amplifier kit night engineering was going on behind its usable feedback to 20 - 26 db. This closed doors gening the design down and method can reduce distortion compo • using Ultra-Linear TO-GOO output trans formers driven by push-pull KT77s. A devcloping the kit packaging, Ctc. In laIC nents by a fa ctor of up to 20 to 1. similar amplifier kit was sold under the ! 959, the first of the Citation line was introduced ro the press. The Citation 11 Hegeman felt rhat a "multiple loop" Radio Shack label as the HK-210. In late method to increase the overall fe edback 1960, EICO brought out the HF-89, a ($159.95 kit/S229.95 assembled) tube was the answer to providing lower distor beefy lOO watt ster<.:O amplifier kit with stereo power amplifier was introduced tion without sacrificingstability. push-pull EL-34s. Lafayeue introduced first and shortly after, rhe Citation I Multiple loops become additive if their the KT-550 in late 1960. The KT-550 ($159/249) tube preamp began selling 10 ratio is adjusted to the relative degree of was actually designed by Stewart the public in early 1960. The first equip- VACUUM TUBE VALLEY HARMAN_ KARDON CITATION I AND I I �Iii .� -, We don't pack an engineer into each new Citation Kit but ... .••the engineerina: buill i,,1<> t'ac" kit Rigid terminal bo.1rds arc provided for Tilt: CITATION 11, HO \1'"" Su,�". is eo .'r.. ci .... th,,1 Ih .. unit con�lrucl.,.1 mounting resistors anu condensers. Once "/'o,,;c Po,,;c, Am/,Ufk,. l>.�s � l'<'ak powcr of In· in the honte will be Ih.. "'Iunl 01 tbe mounted, these components arc suspended OUlput :!:GO \\'�III! This rC1I1arkablc Slru_nl rCI>n..J.uC': r"-que",,," :u (aclorf-Ilroduceu '''til.'''''''nt. tightly between turret lugs. Lead length ,,�H la,," as 5 e)'ek, "I,\uaUr Without Ilh�,� .h'ft. and issharpl}" ucfinoo. Tht uniform SV.1cing of It is far more djfflcult to uesign a kit frequ"neies III higb �s 100,000 e)'cI" with. components and unifnrm lead length than to produce a completely manufac out 311)" evidence of in,larnlit)' Or rinl;," , irnure the n\'erall stability of the unit. tured product. In the plant the engineer At IIo""",li.,,,,",", Iceels. lloe old� ID""''''_ Improper routin" of leads. 1)�rticub.rly ,,;on <;ootro1 his design from the moment "ble oil/Or/loo' ill 11,;, ."';/ co"'''' I,om ,I,,, loog leads, can r sult in unstable perfo n· lauO'dlO'!! Ic.th'tl C'Irli",,,ell'. of inception until the final packaging. The e n (TI'e Citation anee. To prevent this. the Cit;ltio 11 f"lIctorr·\\'ircd - kit builder has only his tools, his ingenuity n 11 is - $159.95; $�19.95; c'ln'PJlC(1 with a tcml'lntc to cnnstrud a Charco.ol prown End".",c. AC·2 - S7.9'.J and little, if any, test equipmellt. Cable HarndS. The result: each Allp rice. slightly hlt;h�r in th� Wc.l. Therefore, the comlllc� process of in wire si just thu right le"gth and in just tho right plant production and control ,,·hich aunr- U."'.1n_Ka,doo h�. pf<1',, Build the Very Best CITATION KITS by kardon VACUUM TUBE VALLEY ID H A R M A N � K A R DON CITATION 1 AND 1 I with tWO additional potS on the top of the chassis. The earlr Citation lIs had a larger black-faced S Nice Things Come in Big Packages The amplifier was beefY in siu and weight. Dimensions well' 16 3/8 inch(� wide, J 1 1/2 inches deep and 9 inches high (41 .6cm br 29.2cm by 22.7cm). Finish was gloss charcoal brown with gold highlights and lettering. The bottom plate was light champagne gold and made of either iron or aluminum sheet metal. An optional perforated metal tube cage was also available. When sold as a kit, the. three transformers were shipped in a sep arate box thal weigh«i in at 50 pounds (22.7 Kg). The cotnpJeted amp weighed 60 pounds and shipping weight was 70 pounds! Speaking of OUtput transforme.-rs. the; Citation Il's were outstanding! They distortion produced. Thus, if onc s(ag� The front-end of the amplifier starts were huge, wdl-potted units that had has twice the distortion of anoTher, it with a J2BY7A as the input amplifier dri eXtremely wide response characteristics. should have twice as much feedback ving a pair of 12BY7As as a long-tailed Leakage inductance in these transformer� around it. The three fe edback loops phase splitter which in turn, drives a pair was kept to an absolute minimum and employed in the Citation 11 include: ont of KT88 beam power pentodes. Later the distributed capacitance of the primary from each 12BY7 driver tube plan� !O its versions of the Citation 11 were shipped halves were carefully balanced against own grid, onc from each KT88 Output with Tu ng-Sol 65505 which were men each other to maintain nalUral resonances tube plate to the opposite driver grid and tioned as the recommended replacemem of the unit well above 200,000 cycles. onc from the secondary of the OUtput in a 1963 Ciration newsletter. The massive design utilized the highest transformer to rhe cathode of the 12BY7 grade core malCrials a\'lIilable which low input Slagc. With this design, 32 db of Bias for the Output tubes was indi\,id ered the effect of core distortion to a overall ftt dback was achieved in the ually adjustable with fo ur separalC polS Il'gion well �Iow the limit of human Citation 11 with unconditional stability. on the back of the chassis. Bias readings hearing. With fee dback, the Citation 11 were read using the handy built-in meter transformers were capable of high fre Circuitry of the Citation 1I and a six position switch. The AC bal quency response up to 270,000 cycles! ance was also metered and was adjustable The power amplifier consiSl� of 111'0 identical 60 w.atT cominuous rated power amps on onc chassis with a shared power supply. The power supply is a low-resis lance voltage doubler type with silicon rectifiers, more than ade VACUUM TUBE VALLEY HARMAN- KAROON CIT AT ION I AND I I • ...... � - > .... - ", ' - '" . >"'"- H .. 11i�"" · ...... •- _ -j .. �i � : � . . - IS DJ ' " • i �"n I '. ! ; I iH , ''1it l' ' ! I I .•• . h ;: � il;.i!. , ! ":; .�[-':":':' - - , • j;!• , N' ' i ,1 ·1 ' . p., . •I • ;:.� ! � VACUUM TUBE VALLEY .. ------ HARMAN- KAROON CITAT ION I AND I I Feedback: 30+ db Hum and noise: Beller than 90 db below 60 watts Sensitivity: 1.5 voir RMS input for 60 wam Power consumption: 350 watts Restoration of the Citation IJ Ovet the years, 1 have personaH), owned several lis and have fo und them in aH types of condirions. Ty pically, rhe lOpS of the transformers had scratched or scraped off paint. Some wefe missing melers Of bias adjustment switches, many had broken or missing tubes and all had leaky capacitors. If you are planning to listen to and use a 11, careful planning is in order for propcr rcstoration. Items 10 consider include: replacement of all e1ec Holytic capacitOrs, replacement of all cou plin and bypass capacitors, replacement There appear to be three distinct vari· you can be sure the new owner was very g of all power suppl), diodes, checking and ants of these transFormers: the early ver pleased. replacing drifring value resistors, checking sion had cloth tubin to guide the wife all wiring for shortS and bad solder joints, our of the bottom 0l' the transformer, rhe Factory Specification of the Citation 11 possible replacement of tube sockets with next version had rubberized cloth wiring Sustained power Output: 60 wattS per modern ones, testing and replacement of for the same purpose and the last version channel all tubes. had the wire going through rubber Peak power outpUt: 130 wam per ch annd grommets on the bottom of the can. Many Cit VACUUM TUBE VALLEY .. H ARMAN. KARDON CITATION [ AND [ [ pentode front-end cannOt possibly sound good and that �II tubes in the first audio and phase inverter stages must be triodes. This theory has resulte<1 in thousands of Citation Jl amplifiers being hacked up by audio experimenters. If the amp is � bas· ket case cosmetically and not worth restOring or collecting, it might be ok to experiment with front-end tubes like the 12BH7, 6CG7, 6FQ7, etc. Remember, howe,·er, that the circuit parameters, "oh ages and tube pinouts will all be different and taking on a project like this is a lot of work if you wam to do it right. Some folks have even use 6SN7s in the front Citation / end by cuning OCtal sized holes in the chassis_ Many Citation 11 amplifiers ha'·e been killed fo r the transformers to build you change the mounring hardware. You inferior. The six 12BY7 video pentode custOm amplifiers, which in some cases can also try single-value axial elecrrolytics from-end tubes are still available from sound worse than the original and wind wired in S(ric:s or individually, if rated at mail-order tube dealers and Hamfesu, up having little resale value, except for a higher (350 +v) voltage. etc. Good 12BY7 brands to use are the transformer set. RCA, Sylvania and GE. Avoid Japanese The Sound of Citalion On the Cita(ion 11, the original black types that arc often rcbranded as plastic paper coupling capacitors are Amperex, CBS or Raytheon as they are For tWO and a half years, J used a f located on the bottom o the twO termi lru reliable and ty pically more micro stock Citation 11 in one of Ill)' home )y� nal boards. To access them for removal, phonic. tems and was imprrued with the more it may be necessary 10 remove the screws than ample headroom, ease of high fre holding the boards to remove them. Diodes do go bad with age alld heal, quellcy passages, big soundstage and solid, Some nimble fingered rypes can also Iry contrary 10 some �expens." Ir is best to right bass. Speakers used in my system 10 remove the caps by de-soldering them replace both the "ohage doubler diode were Klipsch Chorus ones for progrruive first. For replacement coupling capaci bridge and the bias supply with newer sil rock and jazz and Acoustat Model 11· IOrs, try Hovland Musicaps, Kimber or icon diodes or the new, high speed types MHs electrostats for classical and acoustic Rc l-Caps, They are ,xpensive, but worth for the best reliability. music. Tile Citation 11 drove the more it in gcar you plan to lisu�n to. They will inefficient Acoustats with ease in my large Modifications - Worth it ? open up the wund.stage mu(:h bener th:.l.n listening room. In fact, the Citation 11 NOS Sprague Black Beauties or Vitamin Most modifications of Citalioll lis was the amplifier of choice at the FM Q oil types. Some of the other "designer� revolve around replacement of the 12B\7 tuner shoot-out #1 in 1992. Several capacitors can sound harsher to sensitive pentode fr ont-end circuitry. For whatev members of the Northern California Tube: ears. er reason, some tubeheads insist that a Enthusiasts present commented on how The ulrilllall: OUlput tube for the It is the original GEC KT88. However, this vintage glass is extremely rare and cosily. GEC KT88s have a rich upper-bass and a glorious mid-range_ The highs are sweet and extended but rhe low bass is nOt as tight as a good 6550. I have used all types of 65505 in the Citations. The lu ng-Sol 65505 are typically your best bet, but are now quit·e expcnsi,'e. They warm up faster, have sweeter mids and highs, but do not have the �5Iam" ty� bass some people like. On the other hand, the GE-6550As are less expensive, have stronger bass, but are harsher on the tOP end and take at least an hour to warm up before they sound �rable_ The new 6550C $vedanas (flash geller) are improved with better tube burn-in and aging at the factory and feature a gold plated grid wire. They have the b� of the GE·6550As, but are w�rmer in tht mids and highs. The new Svetlanas are mOTe bias stable than the early clear top version of this tube, which is noticeably VACUUM TUBE VALLEY .. HARMAN- KARDON CIT AT ION I AND I I ahead of its time. When used with a Cimion II and the right speakers, the results were outstanding. As a vintage pi({:c of gear, it has ilS limitations due 10 the high number of capacitors in the cir cuit that give the sound a veil or haze and seem to limit the high-frequency response. If you plan to actually liSlen to the Citation I in your sptem. you should consider a complete re-cap job using modern polypropylene capacitOrs in all signal path applications. Also, resistors should be checked for drifting values and replaced with newer carbon film or high quality types, especially in the signal path. The electrolytic capacitOrs should bc replaced as should the older silicon diodes with low noise - fast switching diodes, such as the International Rectifa,r HexFREDT.\i type. When restoring das sic hi-fi equipment such as the Citation I, remember to take your time, be neat and natural the amplifier sounded. I prefer output coupling condenser in the feed do a good job. the Citation [[ for popular music because back loop. it is very live sounding, with big punchy Sound of the Citation I bass. Others listeners insist that the 4. D.e. via silicon rectifiers on all If a good restOration is done, {he Citation is tOO hard soundin for classical heaters and low noise resistors in critic.!1 g Citation I can sound excellent, with full or acoustic music. Some feel that the areas. fr equency response, and clear, musical pcmode frolll-end limits the sound quali 5. Separate turnover and roll-off highs. According to some tubc emhusi ty and try to modify the unil by putting equalization controls for continuously asts who have restOred a I. rhe sound is uiodes in place of the 128Y7s. I think variable phono equaliza.tion. similar to a Marana :I odd 7, but with this is kind of a waste because the origi ... more features, such as the stepped aucnu nal designer knew what he was doing. If 6. Continuously variable blend cun ators and full fe atured phono stage. properly restored and used with the right trol control acting as a third channel con Other tube audio hobb"i$ls have taken music and speakers, the Citation 11 is a tfol or a crossfeed control if center chan tube stages OUI of the reamp and simpli brilliant performing amplifier however, It nd is not used. fied the circuit becausep they were unhap is definitely not for the typical single py with the stOck sound after restoration. ended fanatic. 7. All inpulS and Out utS on the Remember any significant modifications samc plane in the back 0r the chassis. will affect the value and resale potential The Citadon I is Born Heavy-duty 14 gauge me[31 faceplatc. to a collector of vin[3ge hi fi. Within a rnomh after the Citation 11 Heavy-duty potted power transformer kit was introduced to the eleClronics press and smoothing choke for B+ vohagcs. In Conclusion to assemble and review, the Citation I In their day, the Ciration J and 11 ($159/249.), a matching tube stereo pre Citation I Specifications were the hot set-up for high performance amp Frequenc)' reslx)nse: +0, -.5db. 5 - 80.000 ')'cb kit, was unveiled. It was an impres audio. They provided more waitS and sive, full-featured unit with 18 stages fea Distortion: I.css th�n .05% at 2 volts OUtpUt sound for dollar than almost any of the turing nine dual triodes (rour compctition. If thesc units arc obtained ECC83fl2AX7and five ECC8 Ifl2AT7.) Total noise: Less than 85 db bdow raled output (high level) by the reader, they should be kept stock if you arc collecting them, but if you will be Some of its unique features were: Assembling the Citation I Ki I using them in your system, do a careful I. Separate baS!; and treble step-type The assembled version of thi� unit job in restOring them and you will be tone cOlllrols for each channel. To ne COSt $100 more than the kit version. It rewarded with a very versatile and power cOlllrols completely out of circuit when typically took over 30 hours for a begin ful audio amplification system that rivals in the flat position. The S[epped bass and ner to assemble a Citation I ki t. The pre contemporary tube amplifiers costing up treble controls had fo ur boost positions, amp consisted of five basic scctions: two to 53500. one flat and five CUt positions. Each bass military-type phenolic terminal boards, Citalion 3, 4, 5 and 10 will be cov and [(eble switching position was careful onc for each channel, the main chassis, ered in a future vrv article. ly contourcd for optimum response and the front pand and Ihe power supply. a minimum of Ireble ringing. The assembly job required patiencc and References: some degr« of skill with hand tools and 2. Each amplification stage was flat soldering. You can bet that when it was I. ElmTfmio Ir'o rld, June 1960. Z. A�d,u, over a wide frequency range and was sur done, the new owner was thrilled. January 1960, 3. Audiu, December 1960. rounded by a feedback loop. Original Harmon-Kardon Cilalion fa ctor} Restoration of the Citation I manuals and Ha,mon-Kardon ca{aJog�. 3. Anode fo llower OUtpUtS extended Whcn first introduced, thc Citation I low frequency response by including the was a revolutionary preamp wilh fcatures VACUUM TUBE VALLEY • HARMAN- KAROON CIT ATION I AND I I Purple Speaker Eater Citation 11 Mod California Style by Charlie Kitdeson In his typical Southern California style, oan Settle of San Luis Obispo has come up with another crea{ion. This time it is a modification of the Harman Kardon Citation 11 called: Tile Purple Speaker Ellfer. The amp was completely stripped �nd rewired with teflon coated silver wire on cemmic u:rminal strips from an old Te ktronix scope. Power supply was beefed up with four 1800 mfd@200 volt filter caps for the voltage-doubler supply. All diodes were upgraded to 1000 volt at one amp premium units. pulled OUI an adapter sockel Ihat 1�T!nit Power resistors and signal resistors were ted a 12B4 triode 10 be used as Ihe phase upgraded with premium units. Oan even ill\·ener. With th� 12B4, the bass was included � solid-state time delay that too fo rward and the mids and highs were lights the filaments firS[, then 45 seconds more recessed. later applies Bt to the plates of the KT88s. Needless 10 say, we went back 10 ,he 12BH7. Overall, the modified unit was The frolll cnd was complttdy rc-dont tighter sounding than a slOck, reSlOred john d. eckland with new ceramic and gold !Ube sockets, £qo"H'''_ Citation IJ but was more refined. [n a c... , __ •• ,""_ the usual removal of the 12BY7 pentodes _...... ,.._ o...ro._ .... , laler issue of vrv, we will feature more --""'.". which were replaced with an EF8G ..... fifSl derail on this modifiatlion and other audio, one-half of a 12BH7 dual-Itiode Citation JJ mods. as the phase inverter and a 6GX7 eye tube tied 10 the OutpUt of {he amplifier!! The power tubes were a set of original Genalex KT8Bs in like-new condition. oan knows an excellent powder coat ing oper.l1ion in San Luis Obispo who finished his amp in candy apple purple with 101.$ of clear coat for a super deep gloss effect. The fr ont panel is done in platinum powder Coat with the same clear coaL Transformers are done in gloss black enamel as they couldn'{ be powder coated. We auditioned the amp at VTV offices �fter a r(X:enl flea electronics mar ket and did some tube rolling and listen ing. Firs!, we tried the amp with the 12BH7 and noced the sound 10 be solid, with tons of headroom. The modified Citation easily drove the inefficient SW DM liDs and filled the room when hooked 10 th� Klipsch Chorus ones. The: highs were sweet and extended, bass -as solid and powerful and the mids were.... good, bUl not outstanding. Then Dan VACUUM TUBE VALLEY .. CATHODE B 1 A S DESIGNING FOR SOU N D � isn't helped, rithu, by unscrupulous man sound engineer will tell you that the goal Cathode Bias ufacturers, dealers, and mag;rzinc review of movie sound is not accurate sound ers who fttd the audiophile's compulsion reproduction, but TO create an emotion in by for better sound with V1IriOU$ �$nake-oi r the \'iewer. Thus, in the same wa\, movie 1_ -- John Atwood solutions. The result is a constant rurn shots are staged and edited, rhe \�ork on a o,'er of equipmem and une:uy fr ustration motion-picture sound-stage is to create, with the: sound qualiC)'. modify and enhance the sound to com· plement the action on the screen. O\·er Designing for Sound High-end equ' mem designers hav( time, certain sound stereotypes have generally polarize;r into the �me{er-rtad One of the mOSt misundt:rstood developed (a movie gun-shot sounds cr� and �golden_earM camps. What each aspects of audio design is the impact of nothing like the real thing), and these side won't admit is that theY n�d each sound equipment on the nature of the stereotypes must be preserved. Other other. The meter-readers need ro actually reproduced sound. Whether we like it or techniques ha\·e been de\·eloped in effons use ,heir ears and admit that their mea· not, all equipment (both electronic and to impress the audience, such as loud suremenrs don't lcll the whole slory about acoustic) leaves its imprint on the sound effects, surround sound, and [he sound. The golden ears need the engi passing through it. In purist audiophiJe �SensurroundH. The important point, neers to keep theiT equipment reliable systems, this imprint may be nearly though, is that the sound reproduction and need measurements to keep their sys insi nificall l, while in a guitar amplifier, exists 10 suppOrt a visual image, nO! 10 bee l? tems from degenerating into a miasma of the tmprint often iJthe desired sound. enjoyed on its own. conflicting colorations. Above all, the The misunderstandin comes about from g audiophile consumer needs to use his ears both the des igners an the users of audio The trend tOwards �Home Thea[re� d and cultivate an understanding of what equipmellt. The designers can have vari installations in the home is an effort to high-quality sound is like. ous ideas about the sonic imprint of their bring the impressi\'e audio effects of a llIovie theatre into the listenin room. It equipment - ranging from denial of the Casuali L stening g imprint to Strange theories on the cause also is an acknowledgement ofthe poor Casual listening is defined here a) it of the imprint. The users may not under sound of regular TVs. However, rhe exag listening situation where the prime goal is stand the relationship between what they gel"llled dynamics, synthesized hall to enjoy the music as reproduced, nOt hear and what they want - resulTing in acoustics, and disregard for phase coher recreare a live �rformance. Strict accuna them specifying one thing while actually ence makes home theatre poor foreither cy is nor necessary. and actually is nOl wanting another. I am in the process of high-end or casual listening. People who desired, since some colorations arc need trying to son OUl these misconceptions. replace their hi-fi system wilh a home ed to mask deficiencies in the recording SOllle of the different needs and miscon theatre system or those who rely on home process and playback environment. ceptions for various cate ories of audio theatre for casual listening will be disap g Casual listening can take place on any design will be discussed below. pointed. thing from a good hi-fi syStem to a High-End Audio decent portable nadio to a car audio sys Elevator Mus ic tem. The key here is to make the music High-end audio i� the dircct descen Elevator music, easy listening, back enjoyable, and that means: balanced, but dan\ of the "high-fidelity� mOvement of ground music, and Muuk® all have the not excessive frequency reSpouse, moder Ihe 1940s throu h the 1960s. The engi purpose of pro\'iding a musical wall g atdy low diSTOrtion with even order dis neers of hi-fi :mdio equipment constantly paper: a nondescript background noise tortion products dominating, and an strived for less distortion and more accu that triggers positive responses in the absence of non-euphonic artifaclS (such rate reproduction. The cUlllularion of this brains of the listeners, without distracting as "digititis,� crossover diSTOrtion, and was Harry Pearson·s concep t of the them from their work. Pioneered br interrnodulation distortion). "Absolute Sound� - the illusion of live Muzak in the 19305 and ubiquitous musicians playing in your living room. The most common problem with today, background music distills the To even remotely approximate this casual listening is that the rep roductiun essence of music to a bare minimum, yet requires minimal coloration of the sound systems most commonly use d (cheap recogni:t.able fo rm. Recent relatives of ele and extremely careful rniking and record stereos, car Stereos, boom-boxes) are pal vator music include new-age music and ing techniques. Individual enthusiasts can lid imitations of true hi-fi syStems. They �ambient" music. lavish time and money on syStems that have tOO broad a frequency response, often are far less eolored than even excel cheap solid-state amplifiers with too Although moSl elevator music offends lent recording studios. This leads to an much crossover distortion and high-order the sensibilities of nearly anyone with ironic situation: thal the more accumte harmonics, marginal digital circuitS, and musical interests, it has been the most sci you make your system, the worse it can speakers with excessive cabinet resonanCb entifically studied classo f music and sound. This is because deficiencies in the (if they have cabinets at all). The result is reproduction of any of the categories list recording studio end of the reproduction ed here. It is also one that is treated as a listening fatigue. Listening 10 a good chain become more and more apparent. 19305 or '40s AM radio would be an ear complete system, often under the control opener 10 the designers and users of this of the same company from recording Stu EfforlS by audiophiles 10 make their equipment. The specs are awful, but the dio to supermarket loudspeaker. As a �yStems sound better are often JUSt unrec mellow, balanced sound is really enjoy result, its implementation, at least by ogni7.ed ;attempts at coloring the sound to able. commercial pro\'iders, is C)ui,e effective. counteract or mask defici�ncies in the This is a sad commentary on the state o( recording studio or recording medium. Home Theatre audio reproduction in other fields. However, overlaying one type of col The movie industry has developed dte oration over another can be unpre art of sound to support on-screen action dictable, especially when the us�r doesn't TO a high degree. Any motion-picture recogni1.e the coloration for what it is. It VACUUM TUBE VALLEY • C AT H 0 0 E B I A S - D E S I G N I N G F 0 R S 0 U N 0 Radio and Public Address Systems mem by car, OU! as guitar companies were Practically speaking, commercial radio bought br big corporaTions, and rcchnolo- :;t/1 broadcasting and public address systems gy marched into the solid-Slate era, many S.E. OUTPUT share the same goal: (0 bring a messa c to amp designs lost the classic tOlle. Be<;ause people: in the most effective fo rm. 0 frten, the 1arcrs still wanted it, though, the TRANSFORMERS this means on:rcomin background noise, resuE { Wali the current surge in amplifier resulting in the need raor compression and mods and classic amp reissues. MODEL PAIZ I. PRICE limited frequency response. This is the Of all the categories, guitar amp CT3KB 3KO l00mA '195.00 case of AM radio. FM radio was fo unded dtsigners and users are the most acutely on the premise of true high-fidelity. MT5KB 5KO 60mA '195.00 aware of the contribution of their equip- However, market fo rces being what they men! 10 the desired sound. The problem VT2KB 2.7KO l60mA '249.00 are, virtually all commercial FM broad- here is that the technical sophistication of castS are compressed to play better in a 'Else 6KO l00mA mOSI players and e\'en ddigners is poor. '195.00 car and to sound �loudcr.� Non-commer- Altcmpn to get the right tone are often "E48B 1.BKO 3SOmA cial FM stations often treat their sound '425.00 hit or miss, with the: rault that many fall the same way because their technicians • back 10 the �safe" designs, such as the ·.50B 20 KHz to 30 KHz cry 10 copy the techniques of the com- 1959 Fender Bassman or 1965 Marshall. • End Bell Construction mereial stations. The result is a disap- There are lots of voodoo and snake-oil • poinllnem for those who listen to FM Secondary Wire Output (No Splice) solutions. Reliability often goes OUt the · ra io in their living rooms for musical For SV8" -3 window, What is needed is 3 bil of scien- _. enjoyment.� For 4 x SV 811·3 60+ Watts tific method and S(:holarly interchange in Public address systems will intention- analyzing and recreating th(' right lOne. Call Our Design Department For ally limit the bandwidth 10 improve Summary Any Custom RequIrement �intelligibility." Since intelligibility is lit- tle affected by amplitude diSlOrtion, litde In nearly every area of audio rcpro- care is taken in the signal path to keep duction is an element of dysfunctionality distortion very low. For simple systems - a persistent gap between the optimum E/eetra -Print Audio 1311 Winwood St. for broadcasting voice, Ihis is nOt much solution to the particular reproduction N, of a liability, but the big problem is th:1I problem and whal the manufacturers Las Vegas, NV 89108 P.A. equipment is often used by the next make or what the users �want.� This usu- 702·646·7990 ally is the rdult of manufacturers' failure Category. ' FAX 702 · 646 ·7752 to improve their designs or th(' brain· Sound ReinfoC(:ement wd shing of consumers with marketing Most �live� performance� tod'ly u�e hype. Solutions to this problem cannOI some form ofsound reinforcement. be legislated. The only answer is eneour- Or Bottlehead Unlike a public address syStem, a sound aging bOlh designers and consumers to says: use their ears and to be aware of what reinforcement system needs to faithfully Hey bottleheads! Hove you built on amp reproduc(' Ihe instrument or voice it is sounds they arc creating or listening to. with TV tubes? E�' 1''' QUADs, amplifying. h actually has Ihe same goal In the future, some of thae issues will be: Lowthu" CII'ld A7's in the same room? as high-end audio, and thus needs as explored fu rther in this column. My goal good electronics and speakers as high-end here is to raise everyone's cOllS(:iousness Did you make a tube output for your CD audio. It actually has a more difficult about th(' sound they are crealing yet? NO? Well quit readin' "'" task, since uniformly good reproduction or hearing. dream in' and 9£t that iron hot. It's is necessary over a large area. time to put your solder where your theory i,. Join VALVE, a 9Onzo, Unfortunately, most sound reinforce· dumpster-divin' tube a.Jdjo club, stuff ment is don(' using P.A. equipment. This is so common that many people come lO your heod with Q monthly new,lefter expect an �dectronic" sound comin� full of rodicol fl.Jbe idUlS, and build from the stage, with all sortS of ani acts. � ..amethin'l Send me 25 bueks ($35 Sound engineers involved in sound rein- overseas) and I'll send you 12 monthly fo reement would do well to study the "��' yeah. wo 9" """ ;,ruo, ideas behind h h-end audio, and use Two years worthl 10 their ears ju �ge their raults. {� • • Electronic MusicaJ Instrumenu Next Time in VTV: FM Tu ner VALVE E1ccHonic amplificalion of musical , T -:; 2786 instrumel11S started as an 3ltempC [o 5illl- Shoot·Out Featuring The Best P.O.Box ply magnify the sound levd of instru- Vintage Tu be And Solid State Poulsbo, WA mel11S. With the advcl11 of rock :Hld roll, 98370 Tuners, Don't Miss it in VTV uitar amps got pushed well beyond their Voice: 360·697·1936 �inear regions, and soon the sound of the itS out Late Summer 1996 Fax: 360·697·3348 amp and speaker became the m2jor part of the desired �lone. � A few designers, Subscribe Today!!! such as Leo Fender, designed their equip- " 1\ ,\ V ACUU M TUBE VALLEY • TUB E INDUSTRY NEW S in {he LA. area, trying 10 make GCA7s, We gOT tWO samples of the ne,' Tesla Tube Industry News �. 6L6GCs and 6V6GTs the way Sylvania KT 88. It is being sold by Groove l ubes � used to. Still no product in sight. I know now and mv teSts show thar ir is excellent. by you guys 3rC reading this: how about ! pu't 500V�t 100 mA into one, and it did sending us some samples? nor protest al all. The new KT88s also had �I::::I Eric; Bgrbour an excellent sound, with rich midrange and Ei-RC, [he valve manufacturing arm solid bass. Should be good fo r all those of Elekuonska lndustrija Nis, Yugoslavia, DYNA Mark J!Js, Citation lis, Mac 275s, has signed an agreement with Edicron 3008 Forever Indeed . CIC. Olll there. More about it in my Elec{fonic Components of OxfordshIre, 6550/KT88 article in a future VTVarticle. The 300B is becoming 50 popular UK under whic Edicron will be respon to h thar Shuguang is rrying marker f?ur sible for the inwrnationai marketing and Hello Out There 11 m (count 'cm, fo ur) versions. Wc obta ed a ts have the exclusive world-wide sales righ . \'(t hen we ran issue ;;I, wo: asked for distributors price list at the recent Winter The first valves ofT {heproduction line CES in us an it st press releases for manufacturers and dis� Ve gas, d li ed all of will be the KT90 in May 1996. For Shuguang's audio tubes. There were a few tributors. BUI nOI much has come our more information comact: Addan Bailey, way. of things listed that had nOI been s«n Most what we do see is either Edicron, Park Road, Faringdon, from readers (usually [elling us how before. In addition to something called Oxfordshire, 5N7 7BP England +44 (0) VTV. . thanks to an "EL34 copy of Mullard," there were much rhey like . .. all), or 1367 243030 (FAX) from transformer manufacturers reacting four versions of the 300B. Onc was �stan to our SE transformer articles in the last dard, H one was �copy of WE, � one had a issue. graphite plate, and the fourth was nOt given any special designaror. C'mon! Why are companies like Richardson and Eimac being so secre Thanks to le Kuo of Quadric live?? only help sales if you are Audio, we obtained one each of the "wpy It can mentioned in vrv. We are read by ofW£" and graphite-plate versions. Borh were in canons marked wilh the Royal numerous OEMs and dealers, in high brand name, which was also on the tubes end, pro audio and guitar amps. So do yourself good e themselves. The graphite-plate unit had and tell us (and our r ad up to! the Royal brand in gold Rash on the ers) what you're insidc of the envelope. ! tested them on our bt:nch amplifit:r, in the same manner as the 300Bs in our report in vrv#3. Running at 300V 75mA, and at 500Y 50mA, distortion a[ I wall into 8 ohms was measur«l. Distortion and Bias a[ 300V 75mA: WE W(S(fe� 300B(l995) 095% ·SIY Shuguang 300B .Itandard .125 -SO Royal 300B �wpy ofWE" .170 -54 Royal300B graphite plat( .130 -SI Hammond is trying IQ get into the SE Distortion and Bias a[ 500V SOmA: uutput-transformer market. We saw one Shuguang 300B mndard .270 ·112 of their 1629SE units, and it wasn't exact Royal 300B "wpy of WE" .590 -122 ly the world's best. But rhey s�m ro be Royal 300B graphite plate .330 ·115 serious about it, and are working on new designs, primarily for 300Bs. The graphire-plate unit looks very The VAle Va lve VV30B and W52B Carb(m interesting. I suspeCt that ir can be run tubes will be available exclusively in their Pidu much harder than any other 300B, and amplifiers. They are allowing no sales to distortion will decline (and sound quality Cbillese DIY builders or OEMs. According to a will increase) as plate current is increased. 300B letter vrv received from YAle owner, The "copy of WE" was indeed very dose Dr. Ri ccardo Kron - "Our retailer experi to an old Weslern Electric in appearance, ence in America has shown that 80% of with wire-hook filament tensioners and a the hobby do-it-yourselfers and small COt center-tapped filament. But you can {ell tage home builders lack minimum know that it is not orig nal, as the geller flash i how in approaching a completely new doesn't look the same and the glass enve G)one electron"" tube and tube technology , in thal copying t"b,>Gm/;v rlcs;g"" allll ",,,.,,/r"'g lope is not top-quality. SI ill, if you are in from old diagrams is nOt sufficient to the market, these tubes are worth trying. O"c [Iccll .... " design." 60S \\.,hirn:t<»' s,,..,.., �UH� u; Rumon s,.,. Cl ..... Calir" n';" 9.5().30 �M VA le is coming uur with a VY300B, f."X �OS9�·� J"hn A".ood There aro: pt:rsislt:1lI stories about a �"",il .",ood(jj",�·.,.1o..1""',<"'" intended as a comparible replacement for EnlO"...... small tube production line being started the WE 300B. http:l'"""·.o!",.�kdron.«>'" VACUUM TUBE VALLEY • TUB E M ANUAL COMPAR SON and continued 10 the end of the Hlbe era still melllioned in detail, but most of the A Tu be Manual Fragmenta Or a (J975). early triodes are barel), mentioned. Few Comparison of Va rious Tu be industrial numbers are melllioned (5881, Each of these manuals contains a 6973, 7025, 7189, 7199, 7591 are), and Manuals wealth of materia\. much of which is only one fo reign-numbered type is men· repeated fr om manual to manual. One By Paul Joscpb BOUIbin tioned. ntt In this article, the author will review RC-I3, J4lmd 15 a number of different manuals in Ihe hope that this exercise will enable the 10 10 reader be able imelligemly choose evcn tht' 'OIA discussed in detail. The the manuals that will be the most useful manual Starts with a discussion of \'acu" for their needs and, perhaps, save some urn tubes. The tnd of the book has cir space and money as well. cuit diagrams showing "typicar examp1e5 of various circuits, as well as tabular tube RCA RC-29 RC-30 information, base diagrams and obsolete and The first company that we will tube information. This fo rmat was fol explore is RCA. Their manuals seem 10 lowed throughoul tht series. industrial and foreign tubes with even be the mOSI commonly available and, more Compacuon television tubes with therefore, merit the closest considerarion. Manual RC- J4 (1940) and the RC non-standard filament voltages. RC-30 They arc the Iype That onc is most likely IS, frOtll 1947, are almost rwice as thick was the last fu ll range tube manual pro 10 find at bookslOres, swap-meets and as their predecessors. While thtre is great duced by RCA and is also the one most mail order book sellers. RCA tube manu derail for the 2A3 and the 6L6, the 10 sought after by tube enthusiasts because it als come in many different types. and 50 tubes are discussed only briefly. has the most tube types listed. As you can Thtre is a nice discussion of resistance see, possession of a smattering of the RC· According to Barry Nadel, who has coupled amplifiers, along with the usual series manuals can give the enthusiasr made a study of Ihe RCA-Cunningham circuit diagrams and tabular information. much of the tube information that he series, the seri�s well! from RC· I 1 10 RC· These manuals were printed at the Start needs. 30 (1975). There were separate RCA of the "Golden Agt� of High Fidelity. Radiotron and Cunningham manuals RCA also produced a loose-leaf, six published prior 10 1932. A single exam· RC-20 - 22 were prillle(1 from 1960 - volume manual called the RCA Tube pie, R-I 0, is known re the aUlhor. It is 1962 towards the tnd of the �Golden Handbook HB- 3. This was a subscription postulated that the �RC� designation Age,� when tube hi fi sttreo became fully $trvice for designers, engineers and techni delineates a combination of the established. They have much illleresting cians where the subscriber would be stnt Radiotron and the Cunningham manual). information for the High Fideliry ampli new tube update sheers regularly to be The "RC� series of softbound RCA tube fier designer and appreciator. Va rious cir inscned illlo their proper places in the manuals staned about (he same rime as cuits used in Hi-Fi lIpplications are dis binders. The HB-3 set goes back to the did the beginning of High Fideliry, 1932, cussed in detail. The 2A3 and 6L6 are early tubes and continues into the sixties VACUUM TUB E VALLEY • TUB E MANUAL COMPAR SON wrinen primarily for professionals and the radio amateur, the information is quite relevant to the audiophile. In the transmitting tube field, however, there were many proprietary rypes, and the RCA manuals only covered tubes manu" faccured by RCA. Sylvania HB-3 of tube information: a loose-leaf subscrip tion-based manual on 8 Ill" x 11" pages, including Nuvistors. The dau on each intended tube is about the same as the best infor for professional design engineers, mation available on the tube in the "RC» and the more common �Essential Characteristics," intended for setvicemen series. The information covers all types of and amateurs. Originally in a pamphlet tubes including receiving, transmitting, form in the late 1940's, it became a spiral Thyratrons, pholOwbes c{c. bound book with the unique feature that Unfortunately, since the Handbook the bottom part of the page containing was a subscription service, the complete: the basing diagrams was separate from the ness of any given set is dependem upon: lOp pan containing the data, allowing the when the original owner subscribed, how Sylvania produced a loose-leaf basing 10 be matched up with the data. diligent and accurate he was in updating Technical Manual during the Golden This format was continued until the [he set, and whether or no! he deleted Age. Editions vary considerably in rheir 19705 when a regular paper.back formal material that he feltwas nOl useful to content. The author's 1951 edition con was adopted. The spiral-bound editions him. Beware: when purchasing an HB-3 tains little information not available in also had circuit diagrams. any other "standard" manual, but the set. Many collectors will buy a set 10 The GE Essential Characteristics remove pages to be used in upgrading 1959 edition is much more interesting. llIanual is different from most other tube their sets, and then selling what was le6. The special purpose audio power OUtput types section shows many of the interest manuals in that it contains only a tabular A set that has gone through this process a listing of data, although a few characteris few times could be worthless. A complete ing High Fideliry tubes from the Golden tic curves of common tubes were given in see is a valuable resource. Age, nOt fo und in the RCA manuals. For instance, one can find the 5930, an the back. The outstanding feature of the industrial equivalent ro the 2A3. Sylvania GE manual is that it lists data for nearly also published a tube manual in booklet all R.MA-registered tubes, not JUSt the fo rm. Since 5ylvania produced, or sold, a ones manufactured by GE. It is a linle few tubes that RCA did not, it is worth SpOtty in the industrial series, bur still has while to get at lease one comprehensive far greater coverage than any other manu SylvaniaTube Manual. ,I CBS-Hytron Tung-Sol Tu ng-Sol also published a loose-leaf set of Technical Data Books on a sub scription basis. These are similar 10 the RCA also produced a pocket si·Led RCA Handbooks. Tung-Sol also pub series called the RCA Resource Book. lished tube characterisric hooks in tabular These were given away by cube distribu· form. Be sure 10 find a late edition if one tOrs and contained base diagrams, RCA is Illterested in information on the 5881 (eH equipmenr ads and tabulated tube and 6550. daea for all cubes made by RCA up to the date of that particular edition. These We stern Electrk handy packer guides also contained oeher Western Electric manuals Covet only useful information. While lacking the their own tuhes. Since Western Electric depth of the larger manuals, they are Ma nual alldSams Tu be data is rarely given in other manu handy for quick reference at flea-markets Book facturer's data books, one has to get a and are small enough (and hardbound) to Western Electric manual to have chat keep on your bench. CBS-Hyrron produced a loose-leaf information. The manuals are in tabular tube manual very similar IQ the Sylvania fo rm and only give specifications for Since many audio designers and manual. It is notable in having its exten tubes that were current at the time of builders arc using transmitter tubes for sive set of characTeristic curves located in publication. Obsolete numbers arc men power output purposes such as the 21 I, the back of the book. tioned and cross- referenced to other WE 811, 812, 8-15, etc., the RCA TT-3 through TT-5 series transmitting tube General Electric manuals can be quite useful. Although General Electric published TWO Types VACUUM TUB E VALLEY • r--======������� ______� � V [NT A G E BOOKSHELF S PEAK E RS tubes in the back. There is no attempt at will be cO"ered, nor will coaxial or triaxial substitution with tub� of other manufac Great Sounds From Vintage speakers be covered. turers. Since We stern Electric made Home Hi-Fi Speaker almost exclusively commercial and mili Most of These speakers arc not meant tary equipment (they did make a wn Systems 1958 - 1969 10 be fo r your reference system or for high-end systems. They will work great sumer radio in the twenties), and since by Charlie Kittleson there: is greal interest in WE tubes in the for second systems, bedrooms, office and audio community. these manuals arc: cov resort cabin systems. Many of these etcd and arc difficult to find. An original speakers were highly rated in their day for onc can be relatively expensive. their balanced, smooth sound and eco Good sounding speakers are one of nomical price. Most are of the bookshelf Vade Mecum th� most important pans of any sound size, but a few are floor standing units A truly international, bUI difficult to reproduction system. Throughout audio which provide a -bigger" sound if you find, tube manual is Vade Meculll. hislOry, there have been uclassic" speaker have the room. Published in Europe, it references tube designs that set the standard for quality Things to Consider When uiring a fr om all major European countries, the listening in their era. In this period of Acq Vintage Bookshelf Speaker System United Stales, Ru�ia and Japan. It is very audio history, speaker research and devel I. Price: A primary source source for useful in that it cross-rcfcrenccs tubes opment in high gear 10 satisfy the from different coumries as well as giving new generationwas of discriminating listener. prices on vintage bookshelf loudspeakers tube characu:ristics. is the Orion Blue Book. The Blue Book New England vs West Coast is fairly accurate in contemporary audio Another type of m:,illuaJ thal is quite During the Fifties and Sixties, there prices, but can be way off with most vin useful is that of the tube substitution wcre [WO major camps of music lisceners. rage audio equipment. Most of the manual. They were issued by many com The �East Coast" or "New England" speakers lisled in this article are mass panies including Sams and Radio Shack. sound really stan(-ci in the IIIid-Fifties market types that were very popular in Most are fairly good and also reference with inefficient speakers like the AR-I their day and still hold some appeal IOday industrial and fo reign tubes. A miliTary and AR-3 acoustic suspension speakers. to music listeners who want to experi commercial cross reference ehan is also a East Coasters, many of whom listened 10 ment. Try 10 avoid paying high prices useful item. Onc must be careful follow classical and acoustic music, preferred a (over $200 each) for any of the speakers ing the information contained in substi drier sound with less boomy bass and a listed in this article. There are other larg tution manuals. The information given is balanced presentation. Their amps of er. higher qualiTY ,·intage speakers Ihal approximate; not all tubes will substitute choice were typically MaranrJ; or Fisher command very high prices because of properly in all applications. which were hooked up TO AR, B01.ak and their unique sonic characteristics which other non-horn loudspeakers. The uWesl arc appreciated by select user groups. Reprints of desirable tube manuals Coast" or uTish_Boom" camp was the have fttently come out. For aample, 2. Condition of Drivers: Avoid other main listening camp of hi-fi listen Antique Electronic Supply has reprintftd speakers with obvious and not so obvious ers. The lish-Boomers liked jazz, rock the 1973 edition of the GE Essential defecTS. Inspect the cones or diaphragms and pop music. They wanted to feel like Characteristics (the laSt one), the RCA of all drivers for holes, tears, etc. If possi. the band was in their living room and in RC- 19 (1959) Receiving Tube Manual ble, try out the speaker and listen for their faces. Big, boomy bass, extended and the RCA TI-5 Tr ansmitting Tu be cone rubbing or other mechanical speaker and bright highs with little or no Manual. A reprint of the Wes tern EI«:tric distonion. If Ihat is nO! possible, bring midrange 'as their choice for the KIi,'e tube data manual is also available. an ohmmeter 10 measure the continuity band" effect..... The lish-Boomers pre Ori inal manuals can often be found by and im edance of the speaker and dri ferred Ntec Lansing or JBL horn-Type mai! from the usual suppliers of vintage vers. I rthey test open, the speaker is loudspeakers hooked to Mdntosh ampli. electronic books. worthless and viJl be very expensive to fiers and preamps. Some listeners of this � reslOre or repatr. Conclusion group with upper frequency hearing loss even used solid-state amps with their Condition of As one can set:, acquisition of the cor 3. Cabinet: It ean be horn speaker systems 10 get Ihal eXlra trt: rect tube manuals can increase rhe enjoy very expensive 10 reSlOre speak.::r cabinets. ble "bite." melll of one's hobby. Remember that dif Do not pay premium prices for speakers with finish or structural problems. Try 10 fe rent manufacturers sold different tubes Why Old Speakers� and other manufacturer's tubes ofTen did purchase speakers with cabinets in good Today, strange as it may seem, most not get into their manuals. A small col condition. They may be slightly more loudspeaker manufacturers are slil1 mak lection of one company's manuals over a expensive, but less hassle. Grill cloth can ing inefficient systems that require high long period of time, augmelllcd with a sometime be cleaned by removing it from powered amps of 60 10 200 watts. few selected ones from other major com the baffle board and using mild deter While some of Ihese... speakers ... sound out panies, will provide the owner mosl of gent, Ihen drying it on a flat surface. standing, many lack the smooth, easy lis the tube applications and specifications However, replacement grille cloth is avail tening sound that may be important in able needed. from some vendors that is dose 10 non-critical applications. This article will the original type and should be consid If you have any questions concerning cover the basics of sreaker components ered. tube manuals or other books of interest and explore some 0 the beuer hi fi pack 4. Crosso\,er: Wax· paper and elec to the. villlage electronic enthusiast, please aged loudspeakers that were popular in reel free to contact me through VTV. the lale Fifties through the Seventies that trolytic capacilOrs typically deleriorate can still provide the listener with pleasing significantly after 20-35 years. This man Copy right 1996 PaulJouph &urbi". sound. Not all speaker manufacturers ifests itself as decreased high frequency VACUUM TUB E VALLEY .. v N TAG E BOOKSHELF SPEAKERS response andlor Md(ad� sounding upper Bowit DriwN frequencies. These capacitors must he replaced with morc modern units if you expect 10 get optimum performance fro m your loudspeakers. In addition, crossover pottmiomclcrs usually go bad, become noisy and/or become intcrmiuent. The� also should he replaced with newer units of the same value. The fo llowing sectiOlls go imo morc derail about speaker cOl1Slrucrion and reslOr:uion. Speaker Cone Construnion and sound may nOt be the same as the origi High Frequency Drivers Materials nal. In older speakers, the high frequency In the so-called Golden Age of Audio cone and dome-type drivers were in Butyl rubber and other rubber com from the post-war through the early developmental stages and may not have pounds were also used by AR, Jensen 1960s, quality materials were typically the the high fr equency extension of the newer and JBL on some of their LE series speak standard and nOl the exception fo r many kevlar or titanium dome super tweeters of ers. With age, this material can deterio audio cquiprnclH manufucrurers. The today. Many tweeters were simply small rate or become stiff, making the speaker same is true for speakers. Many of the cone-lype drivers tWO to three inches in dead sounding. Some speaker U urus� speakers today arc made from cut and g diameter. Others used small horn-type suggest putting a drop or tWO ofautomo paper or molded plastic. In days rweeters of varying quality. Later designs, folded bile brake fluid on the J BL LE surrounds of yore. most speaker cones were made including the Dynaco A-25, used dome to loosen it up. This is not recommend from a combination of paper pulp, felt, type tweeters that can be quite ed and we assume no liability if you try it asphalt, cofton and other materials that respectable performers. and ruin your speaker. were manufactured by a fioar:uion process A problem you may run into when in a slurry that was poured into a brass or Ty pically, for the best durability and acquiring older loudspeaker SYStems is stainless-neel strainer mold machined to quality in older speakers, look fo r compo blown rweeters. In most cases, they can the exact shape of the spC:J.ker cone. The sition paper cones with a felt, pleated or not be repaired easily. For the true col slurry was molded through a variable vac rolled and treated cone edge. Avoid older lector, only the original replacement pan uum process, dried and weighed to exact speakers with foam rubber edges or butyl will do, but that may involve running a specifications. The quality manufacturers rubber compounds, because more often wanT ad in AudioMart or related publica used this method to get the most accurate than not, the foam or rubber has deterio tions. Newer, generic replacement tweet and lifelike sound from their dri\·ers. rated, making the speaker useless, unless ers including cone, dome and ribbon you can find someone who can re-foam The cone edge suspension system on rypes may be used if they are the right the surround. earlier quality speakers was either rolled impedance, efficiency, size, etc. There paper (i.e.: Altec and J BL) or molded fab Magnet Construction are several manufaclUrers and mail-order ric material, either rounded or pleated, suppliers of replacement high-frequency Pro-audio speakers made by Altec aud which allowed for high compliance and drh'ers, so stan experimenting!! long-throws. The surround was typically JBL typically used high-quality treated either with rubber or a viscous machined ALNICO-V magnet material Crossoveu because of its superior sonic qualities. material to protect and prolong the life of Crossover technology and materials Many home speaker builders also used the unit. Early Wharfedale and other have come a long way from the Fifties ALNICO equipped drivers during the British speaker manufacturers used a feh and Sixties. Most manufacturers used Fifties and Sixties for the same reasons. mau:rial for the cone edge, which seems wax paper and foil or oil-filled paper In the Seventies, ALNICO V became to laSt much longer if cared fo r. capacitors in their crosso,'ers. Many of more expensive because it contained so the later designs used bi-polar electrolytic In the late Fifties and mostly in the called �strategic� metals that were being capacitors which were usually of mediocre Sixties, several speaker manufaclUrcrs used in defense eiec(fonics and weapons qualit),. Some collectors and a few listen resorted to the wonder material for conc systems. By then ALNICO was replaced ers leave the original crossovers unmodi edge suspension - fo am rubber. Although by so-called �mud� or ceramic magnets fied because they prefer the vintage this material is still used by the "bargain� made from a ceramic and ferrite slurry. �veiled· sound which limits high frequen speaker manufacturers now, it is problem While some speaker emhusiasu insist that cies. Older capacitors can also soften the atic. The foam tends to deterioratt' with there is no difference in sound, others sound, which may be desirable in horn timt', tt'mperaturt' eXtremes, ci arette claim that the ALNICO magnets ha\'e a g type 10udspC:J.kers. smoke, etc. Many of the low-frequency more �live· or extended sound and drivers from the Sixties and Sevt'nties ceramic have a �duller· sound. Whatever Probably the single most imponam built by Electro-Voice, jensen, Acoustic the case, they do sound different and the fac tor in the performance of high-fre Research, Wharfedale and others are choice is up to the end listener. In addi quency response in old speakers is to unusable because tht' fo am surround has tion, earlier drivers with ALNICO V have replace the crossover capacitors with high deteriorated or melted into a tar-like goo. higher value to collectors than their quality, modern components. Some new There are kits availablc to re-foam these ceramic counterparts. capacitors take some time to break in as speakers and some businesses specialize in they may sound a little harsh when rhe re-foams, but these can be tricky and rhe first several hours of signal are PUt VACUUM TUBE VALLEY • v N TAG E BOOKSHELF SPEAKERS through the speaker. Some brands require regarded now. To get high-frequencies, introduced in the mid-sixties. The 2AX more time 10 break in than others. AR recommended using the JanS1.en was the same as the 2X except that ir fea Generally, new capacitors tend to mellow Electrostatic tweeter with the AR·1 start tured the I 3/8 inch soft dome tweeter OUI and sound smoother with more ing in 1957. Other electrostatic units from the AR-3A and the 10 inch woofer music being played through them. became availablc including the popular had a foam Surround. priced Elecuostat 3 sold by Radio Shack Cabineu and Enclosures starting in 1958. \'(/jth this combination, In most cases, early speaker enclo�urc) the bass was full, dIe mids were 3·D and AR·3 used real mahogany or oak veneer with the highs were smooth, giving a balanced other quality features such as internal presentation. Unfortunately, not many bracing. Older speaker cabinets can be AR-ls have survi\'ed as many "scav. repaired, sanded, re-oiled and re-finished engers· have sacrificed them 10 retrieve for a beauriful piece of audio furniture. the WE 755 driver to sell to the export Generic replacement grill cloth is avail markets or for home experimentation. able from VlIrious suppliers if yours is 1959 ripped, missing or soiled. 1964 AR-2a' For AR introduced the three way acoustic suspension AR-3 (5225) If you find speakers with blown or loudspeaker. It fe atured a 12 inch cloth damaged drivers, they can be rebuilt with surround woofer, a (WO inch dome mid modcrn woofers, tweeters and crossovers range and a revolutionary 3/8 inch hemi for an exceptional sounding system. It spherical dome tweeter. The driver tech can be a lot less hassle to rebuild an old nology was revolutionary for the time and 1959 AR-2a speaker enclosure than to make a new created quite a stir in the audiophile cir one. cles and hi-fi show demonStrations. Speaker impedance was fo ur ohms, rated The Good Stuff frequency response was 38 to 20,000 Used speakers call b.: found at flea cvcb. The classic AR-3 was an instam markets, ill classified ads, garage and s�ccess as it was the first of the "East moving sales, electronic swap meets, CIC. 1957 AR-2 Coast" sounding speakers with a bal Tile key is to not buy a lurkey. This can anced, dean and musical presentation, include early sixties speakers with fo am perfecT for acousric jazz and classical woofer surrounds andlor cheap horn or music. Piano and orcheStral music W;l.S co-axial units, which tend to be coarse especially good sounding on these units. sounding or may be unusable because of fo am rot. For lower budget audiophiles, AR The AR-3 was one of the first ineffi introduced the AR·2 (SIOO.) a f\\'o-way cient loudspeakers available and needed With the speaker� listed, you will not acoustic suspension bookshelf in the early at least 35 wattS continuous to get any achieve audio nirvana, but you may be 1958. It was a bookshelf unit featuring a volume. The down side of this in efficien pleasantly surprised with a musical, ten inch woofer and two-5 inch cone cy is that you cannot use mOSt AR speak smooth and balanced presentaTion. The tweeters in a sealed enclosure. Speaker ers with SE or low powered triode amps. highs may be rolled off, but that can be impedance was eight ohms, response was There are several \'ersions of the AR-3, fixed. The sound will get even bener 42 to 14,000 cycles and minimum power and some of the later units (AR-3X) fe a when the crossover capacitors arc upgrad was 20-25 wans continuous. The AR-2 tured a foam surround on the 12 inch ed to higher quality polypropylene units was also popular with the Radio Shack woofer which (>'pically mUSt be re-foamed and the speaker cone has had a chance to Electrostat 3. In 1958, the AR-2 was before the speaker can be plared. break back in again after sining dormant rated as a kbest buy" by Consumer Fortunately, there are a few companies for ten or more years. The more you play Repons magazine. The AR-2 was that can pro\'ide re-foam ki ts fo r the AR- them, typically the better they will begin thought of as a very musical speaker back 3 and other later AR speakers. The AR· to sound. then. Many AR enthusiasts preferred the 3A had a soft-dome mid r;l.nge which was first version of this speaker for its richer not as hard sounding as the AR-3. The following is a list of manufactur midrange presentation. \Ve had a pair of Older AR speakers can sound ki nd of c:rs and some of rheir better sounding ear AR-2s in the vrv offices for evaluation "thick� if thC)' have been sitting for a lier units. This list is by no means com and were not very impressed. The highs while. If they are played and re-broken plete, but it does include some of the were very rolled off, the mids were ,·ery in they will Start to sound better. more common units that can still be recessed and the speaker was unmusicaJ. Another problem with AR units are the fo und used at reasonable priccs (read: We even checked the drivers and the crossovers which must be rebuilt with 525 10 $200 each). crossover and they were functional. new polypropylene caps. The adjustment pot5 are also likely to be noisy and either Resea.rch (AR) Acounic About 1960, AR introduced the AR- must be cleaned or replaced. Edgar Vilkhur introduced the AR·I 2A which was basically the same as the in 1955 as the first AR product. The AR-2 excepT it included the ume 1 3/8' One of the last '"classic� AR bookshelf cabinet was a large bookshelf acoustic dome tweeter as the AR-3. In the early sJX:.l.kers from the 1960s was the AR-4 suspension unit with a 12 inch woofer sixries came the AR-2X (S 122) with a (en (S57) which was introduced in 1965. and eight inch mid-range. The mid inch woofer and a single 3 il2 inch The eight ohm AR-4 was a smaller range was typically a We stern Electric tweeter. The last version of the AR-2 wa� bookshelf with a ten inch treated cloth 755 "pancakc� speaker that is highly the AR-2AX (SI28), a three-way speaker surround woofer and a single 3 112 inch tweeter which crossed over at 1500 cycles. VACUUM TUBE VALLEY • v N TAGE BOOKSHELF SPEAKERS Suggested amplifier power was 15 wam, fine on seven to eight wans of SE tube can upgrade the crossover capacitors and bur rhis unit wiI! Tun fine with seven to power. COIlSlllller Reports in 1958 rated tweeter driver for better upper fre quency ten warts or more. The AR-4 was a very the KLH-6 as a �besl buy" fu ll-range results. smooth little speaker which was almost loudspeaker, saying it had "excellent bass, like an AR-3, except less bass. lr also smooth mids with good, smooth highs." For 1969, KLH introduced the Mod.:! sounded clean and musical with a sound 23 ($99.95), a two-way system chat was stage that belied its physical size. This Latcr versions of lhe KLH-6 featured slightly larger than the Model 6. It fe a s eaker received many positive reviews lWO high frequency drivers, then a single tured a 10 inch acoustic suspension p I from the audio press in its day. A later 3/4" rwecler. This speaker was made woofer wirh a heat-molded cloth sur version of the AR-4 was the AR-4X. h well into the early 19705 and is still rela round impregnated with synthetic rubber. used an aluminum voice coil which can tively easy to find due (0 wide diSTribu The tweerc:r was a molded paper dome be a problem and cause rhe rweeter to go tion and high production figures. Also, t�'pe similar 10 earlier designs with a few out prematurely. some later KLI-I units had foam sur subtle improvements. The crossover had rounds, so look out for that. a three- OSition swirch and a crossover point 0 r1500 cycles. A little brother of the KLH-6 Wa5 [he KLH-10 (S99)\\'ilh cabinct dimensions of Advent 23 1/2 inches tall, 11 25/32 inches wide Henry KJoss started the Advelll and 8 314 inches deep. It featured a ten Corporation in 1970 after he sold his inch acoustic suspension woofer with a holdings in KLH. Kloss relt thar there single 3 1/2 inch cone-type twectcr. was a fu ture in home theater and with Power range was 12 to 60 wans. The Advent, he produced and sold tck-vision KLH-IO was available from the lare projcction systems and related audio - Fifties through the mid-Sixties. equipment. Kloss introduced the Advent acoustic suspension loudspeaker in KLH innoduced the KLH-17 1970 KLH 22, 10, J 1 as well. It was onc of rhe largest selling ($69.95) in 1965. It was a smaller book acoustic suspension speakers of all time. shelf with dimensions of23 114 inches KLH The Advent speaker fe atured a foam sur tall, II 3/4 inches wide and 8 114 inches round woofer with a 9 inch piston on a Henry K[oss was designing quality deep. The 17 fe atured an ten inch cloth 12 inch frame similar to the woofer used loudspeaker systems for AR in the mid surround acoustic suspension woofer and on the Dahlquist Any Advent fifries. [n 1957, he left AR co start his a 1 3/4 inch direct radiator tweeter. The DQ-10. speakers you find today will ha"e deterio own company, KLH. He had a number 17 featured a three-position switch in the rated foam woofer surrounds and should of different offerings including bookshelf back of the speaker to add or subuact 2.5 be rcfoamed. The high-frequency driver unirs, large floor standing cabinets and db of high frequency. This is actually not was a screen-covered mid-tweeter shaped the famous KLH-9 electrostatic pane! a bad sounding speaker for smaller listen like a hard donut with a high-frequency speakers. KlH speakers were made in ing rooms or second systems. For bener dome in the middle. great quantities and many are STill around performance, you can upgrade the because They were favorites of the time. crossover capacitors and the ("weeter wirh Advents were very popular with col Kloss used cloth and fabric molded a newer dome-type unit. lege students and other audio enthusiasts speaker cones with a special formula of on a budget. They were available in a From the mid-Sixties through the couon, wood pulp, asphalt and wool. "utility cabinet" wirh vinyl covering made Each cone was made under right colet mid-Seventies, KLH sold seveT31 versions 10 look like real wood and a deluxe vet ances for of an even smaller bookshelf speaker. dimensions, rigidity and weight. sion wirh real wood veneer sides. The 2 These were typically sold in pairs for The resulr was balanced sounding Advent had a right sounding bass with under $100. Some of the models includ speaker. prcrry good upper ranges. It was popular ed: KLH-22, KLH-24, KLH-32 and to "stack" twO pairs of Ad"enrs to get that One of then first widdy available others. The cabinets were all smaller (19 �waJ1 of sound" eITecr. bookshelf speakers was the KLH-4 ($209) 3/8 inches tall, 10 7/8 inches wide and 7 fe aturing a twelve inch woofer and twO 3/16 inches wide) rhan rhe KLH-17, hut Several versions of Advent speakers smal! cone-type tweerers with a duee-way fe atured the same eight inch cloth sur were sold including the four ohm �Baby" crossover variable at 1500 cycles and round woofer and dle I 3/4 or two inch Advent which used a six inch woofer and 6000 cycles. The KLH-4 is less common direct radiator tweeter. Look for the a dome tweeter. Babies image vcry well because of its higher price and lower pro models with hand screw type speaker ter and put Out a lot of sound for their size. duction. minals, and avoid rhe ones with the ReA They are a bargain if found at garage sales jack inputs or two flat-head screws, as or flea markets. For 1958, the: KLH-6 (5129) was these typically have foam surrounds and introduced as a full-range bookshelf unit. may use lower quality marerials. Dimensions were 23 112 inches tal!, 12 5/8 inches wide and 11 7/8 inches deep. Though they are small, these speah:rs The KLH-6 featured a 12 inch cloth sur can sound great with tube amps, includ round woofer and TWO smal! cone rype ing integrated units with 5 to 15 warrs of high frequency units crossing o"er at continuous power. They have a fairly 1500 cycles. The eight ohm speaker was large soundstage and are "ery smooth typically rated for between 20 and 60 sounding in the typical musical spectrum. warts continuous. However, the speaker They do not ha"e strong bass, nor do is relatively efficient and will run JUSt they ha"e super extended highs, but you KLH23 VACUUM TUBE V A LLEY • v N TAG E BOOKSHELF SPEAKERS Bozak 1/2 inches deep. Another good sound Rudy BoUlk began sellin� his speakers ing, but /"lire BOUlk large bookshelf is the 10 t],e hi-fi marker in 1949, beginning 401 B Rhapsody which has a single B-199 wirh the famous &ketrle drum" unit. woofer, a single B-209C midrange and a Throughout the Fifties and Sixties, a wide 200Y dual tweeter arT1ly. The 40 I B is line of high quality speakers were sold, very balanced with good efficiency and nice soundstage. alrho�gh m<;,st of Them were larger, noor standmg unllS. A few bookshelf unitS The sound of Bouk speakers is big, were sold in (he Sixti(S and e:lrly warm and inviting. They are ,·e ry ple:ls Sevenries which were fa irly low in ro p ing 10 listen to with low to mid-power duction. Heathkit even offered a fe w range vintage tube equipment. Many speaker kits using Bozak components in type of Bozak loudspeakers were sold and the Sixties. usuaHy Ihey can be purchased for reason DJIlIICO A-25 Bouk tried 10 standardi;/.e compo able prices. nems in their speaker systems so they Dynaco could concenuate on higher-quality Other NO /llbies: Onc of the mOSt popular producers of materials. large, high quality ALNICO amps and preamps, Dynaco introduced a V magnets were used with cast aluminum UTC Minimax line of speakers mining in 1969 with the speaker frames or baskets. Speaker cones Made by Goodmans of England, this A-25. Dynaco used Bang and Olafscn of were high-quali[)' composition-type with mini-monitor had a rour inch, long Denmark to manufacture their speakers. cloth surround edge�. �gend has it chat throw woofer with a dome tweeter. The Rudy used horse hair in the speaker cone Minima;( had a big sound for its size and At $79.95, the A-25 was onc of the macerial. The tweeters were typically alu imaged very well. These may be hard to largest selling acoustic suspension speak minum cone-[)'pes with rubber damping find as they are not very common. ers ever produced. It fealUred a ten inch to reduce harshness. butyl rubber surround woofer made by SEAS of Scandinavia, with an aperiodic The low frequency Bouk driver was the B-199A 12 inch woofer rated at 20 �('sign sloned and friction damped port. rhe tweeter was a onc: and one-half inch wattS with a response of 40-4500 cycles. dome tweeter made by SEAS which The tweeter was the B-200Y, a twin- cone crossed over at 1500 cycles. It also rea three and onc inch diameter aluminum lUred a five-position stcpped attcnuatOr cone unit rated at 20 wal1S and a twceter connol. Frequency response was response of 2000-20,000 cycles. These 47-20,000 cycles and power handling were typically combined as the B-207A, a capacity was 35 wattS, but you could run two-way coaxial speaker. Mid-range dri them just fine with ten wan amplifiers. vers were the B-209B six and one half inch sandwich fiber cone or aluminum The A-25 was the first bookshelf cone (later), rated at 20-40 wattS and speaker that imaged well. The sound response of 200-3500 cycles and the B- came MOUl of the bo)(� and was very linear 800 a full r.mge aluminum cone eight and natural sounding. In an OClOber inch rated at IS watlH with a response of 1969 product review of the A-25, Audio 35-20,000 cycles. magazine noted That the speaker gave the Some of the mid-sized floor-type best square wave response of any speaker Rectilinear they had tCSted 10 date, regardless of enclosures (if you have the room) price. Audio also felt the A-25 had a rcl include: B-302A (S261), a three-way In the bile 1960s, Rectilinear intro atively uncolored and neutral sound. In with one-B-207A cou and one B-209A duced the popular Rectilinear III (5234) our listening tests of vintage speakers, midrange; dimensions on this unit were a floor standing unit with dimensions of mast VTV associates agreed Ihat the A-25 24 inches wide, 30 inches tall and 20 35 inches tall, 18 inches wide and 12 soundL'(] as good as or bel1er than many inches deep. The bigger brother to the inches deep. The eight ohm unit was S750+/pr modern speaker syStems. The B-302A was the B-305 ($397) which fea verv sensitive, so it could be used with new re-issue A-25 from DynacolPanor tured an additional B-207A coax and had lo\\;-powered tube amps and had a very Corporation seemed 10 have less dimensions of 40 inches wide, 20 inches natural presentation with a nice sound midrange rcsponse and should be broken deep and 31 inches lall with a rated fre stage. It was considered one of the very in for maximum performance. quency response of 35 to 20,000 cycles. first �transparent" sounding speakers by some listeners. The unit was a four-way These speakers sound great with a 10-75 Other Dynaco speakers of note wan tube amp. system with six drivers per speaker enclo include t],e A-SO (dual woofers), the A- sure. Drivers included four Peerless 35 (larger cabinet), the A-IS and the A- Bouk also sold a few bookshelf sized tweeters (rwo different sizes), a hex 10 (five inch piston woofer with a snJ;;11I units including the B-313 Concerto III shaped Phillips mid-range and an Electro dome Iweeter and a small resistance (5197.50), a three-way unit with a single Voice high compliance woofer. There arc damped slot). Of these, the A-IO should B-207A coax and a single B-209A a few variations of the Rectilinear 111, but be one 10 look fo r because of irs superior miciT1lnge rated at 20 watts with a those who have lived with this speaker r response of 45 10 16,000 cycles. The illla�ing qualities for sal�llite speake agree that the model with the single . applic:t1Ions or smaller lIstening rooms. dimensions of the cabinet were 23 1/8 crossover control sounds better than the inches high, 14 114 inches wide and 11 two-control version. VACUUM TUBE VALLEY •• A u 0 I 0 T EST B E N C H A c M E T E R S Wharfdale suring the amplitude of an AC signal. Many latcr v(;fsions of Wharfedalc The Audio Test Bench I. Peak-to-Peak - This is differenc.: speakers in the Sixties used fo am sur b.:rween the mOSt positive point on a rounds on their woofers which deteriorat by wa\'eform and the most negative point. ed very quickly. A good sounding smaller speaker is the W-25, which is a greal per John A'wood 2. Average - This is the average valuc fo rming mini-monitor which does have a of the waveform, referenced to ground. fo am surround, hut the foam material is Mathematically, this is defined as the longer lasting. integral of the voltage over the period, AC Meters divided by the period. Fulton/EMI In the laSt issuc of VTV, we talk.:d During the Sixties and t:arly Scvemit:s, about DC Melers. \Ve will now tUrn to 3. RMS (Root-Mean Square) - If the Fullon, a Minneapolis, Minnesota based AC meters, or more specifically, AC volt AC signal delivered power to a resistive company, sold a few good loudspeaker meters. Why a whole article on AC load, a DC signal that delivers the same systems including the FMI-80 (S80). meters? Don't most DVMs or VTVMs power would have a value rhat is the This unit was a two-way bookshelf sys have an AC range? Ye s, but when working RMS value. Mathematically, this is tCIll with an eight inch woofer and £\'10- on audio equipment, you need more than defined as the square-roar of the integral Peerless paper cone tweeters. The FMl- JUSt a simple AC meter, often with of the voltage squared over the period, 80 had excellent imaging and was consid unknown characteristics. You need a dividd by the period. ered 10 he open and natural sounding. meter with si nificantly more sensitivity The peak-to-peak method is some than your util ity meter. You also need to times used in RF measurements, and is Recommendations understand the different ways AC signals convenient to use when reading the volt Don't look for Ailcc, JBL or Tannoy can be measured, and choose a meter that age off of an oscilloscope screen. here. Those speakers arc in a different matches YOllr needs. However, rhis method tells us nothing dass and will be covered in future ani about the amOUnt of energy in the wave des. This survey is of mass-market, Uses of AC Meters in Audio Te sting fo rm, and so is tarely used in audio mea home hi-fi units only. Here are some of the tests in audio surements. work that require a good audio voltmetcr: If I walUed an older sp.:akef that The RMS method indicates the true sounded modern and imaged wdl, my • Gain measurementS - Voltage gain amOUIll of power delivered to a load, so is choice would be the original Dynaco is the ratio of Output to input voltage. imponant in OutpUt power measure A-25. sometimes given in absolute num While ments. Since wiw and transformer heat bers (e.g., a gain of25), it is more com ing is dependent on RMS I'oltage and For a smaller bookshelf unit that was monly given in decibels (db), where the smooth and easy listening, I would current, RMs measuremcnts are impor gain in db " 20 • iog(absolute gain). choose the KLH-22, 24 or 32 models tant for power supply and distribution design. However, as explained later, because they arc relatively easy to find • Distortion Measurements and do throw a nice soundsrage for their DistOrtion analYLerS measure the residual implemellling a �lTue-RMS� meter is size. For more bass, check out rhe KLH- distortion through a syStem, whether har more difficult than the other methods. 6, 10 or 23s. In this same category, the monic distortion or intermodulation dis The implemelllation of an average AR-4X is an excellent petformer, with a rortion. If you are working with low dis reading voltmeter is simple, and since its more detailed, refined sound. tonion systems, these distortion producls reading is fairly dose to RMs reading for (I can be quite low, often -60 dbm sine waves, most AC voltmeters are aver For bigger sound with more sound rnicrovolt). Most distOrtion anaiYlers age reading, but recalibrated to indicate stage and bass, look fo r Rectilinear Ills or have built-in sensitive AC voltmeters, you may even try some B07.aks, but with an RMS value for sine waves only. Since although some older ones require an most audio testing uses sine waves, this is those, plan on rebuilding the crossovers externa! meter. for optimum performance. a reasonable compromise. However, if there is significant distortion in the mea • Hum and Noise M",asurements A sp aiaL thanks 10 Roger E. Coon of Measuring the residual noise in a good sured sine wave or the waveform is not Redwood City. California; Earl Ya rrow of audio syslem requires an AC mcter with a sinusoidal (as in square waves, IM distor Fremont, CaLifornia andJohll EckLl1Id of least a sensitivity of -80 db below maxi tion measurementS, or white noise), the Palo Alto, Californiafor their arsiJlanCf mum OUtpUt. Sometimes an "A-weight average-reading voltmeter will not give with thjJ anicle. ingn filter is used ahead of the meter to correcl RMs readings. emphasi7. he noise [hat the human ear is References: � � If the shape of the wavcform is most sensltlve to. Audio Magazine, Qc!. 1969, known, then correction factors can be applied to give correct readings on aver Dependence OTl AC Wavefo rms COnJullltr RtportJ, June 1958 age-reading meters. Since AC signals (an come III many Specilicalions and other information w�re different waveforms, methods of defining Implementations obtain�d from original manufaclurer·s adver how these waveforms arc measured have tisemcms (AR, Dynaco, KLH, Bouk, elc.) Since a sensitivity of at least .001 voh been developed to suit different needs. (I mY) is needed in an audio-grade AC For this discussion, all waveforms I'oitmeter, these meters incorporate a described here arc recurrent waveforms, highly-sensitive AC amplifier, typically i.e., repeat the same wave shape over and over. There are three main ways of mea- VACUUM TUBE VALLEY • A u 0 o T EST BEN C H A C METERS mic convener circuits, or, in the case of newer digital meters, do the conversion in softv ...are. Many hand-held DVMs can b<' used for AC measurements, but have some potentia! pitfalls. They often have limit ed s<'nsitivit)', and their accuracy can be a lot worse than the number of digits would indicate (cbeck the specification carefully!). Even worse, though, is that many DVMs, especially older or cheap<'f ones, are only accurately calibrated in the 50 to 60 Hz range, and can give grossly erroneous readings at other frequencies, especially above 5 KHz. Again check the manufacturer's specs careful!y. Most AC meters have "OUt Ut" ter using feedback to stabilize the gain. An and performing the RMS calculation in a P minals that allow the calibrated high accurate inpU! ancnuaror selects the sen microcontroller. This is the technique gain amplifier within the meter to be sitivity. The bandwidth of this auenua used in nearly all modern true-RMS volt used as a utility amplifier. An oscillo tor/amplifier needs to go from below iO meters. scope can also be at!ached to the OutPUt Hz to well above the highest frequency to to allow waveform monitoring. However, be measured, typically 300 KH7. or more. A probh:m with either the thermocou The hum and noise level of this amplifier ple or synthesized techniques is that there needs to be low enough to not obscure some meters, most nOtably the Hewlet! ,he lowest intended measurements. is a limit (0 the peak-ta-average value that these RMS circuits can validly mea Packard meTers, run feedback around the In average-reading melers, the ampli sure. In both techniques, the dynamic meter rectifiers, as a way of linearizing fier is followed by a rectifier and filter cir range of the AC ill PUt amplifiers limits the analog scale. (Most OTher AC meters cuit to convert the AC waveform into a the peak signal that can be accommodat have scales that get cramped at low read DC value. This value is then displayed on ed. The synthesized RM S scheme also has ings). The effect of this feedback, either an analog meter or digital display. errors and dynamic range limitations in though, is to put a nOll-linear kink in the multipliers andlor conveners. The the output signal at low voltage levels. Th,;:r;: aTC twO main schemes to mea key spec to look for in True-RMS meters This kink is below the minimum meter sure RMS voltages. The traditional is the maximum "crest-factor� they can reading, but is clearly apparent on an method has been 10 use a bolometer or handle. oscilloscope. This limits the usefulness of heated thermocouple (see figure 5 next H-P meters as general-purpose ampli page) to convcr! the AC signa! into a DC Th ..re are twO types of display: linear fiers. value. Since the temperature of a resis(Or and logarithmic (see figures 3 and 4). The is proportional to the power dissipated in most common is the linear scale, which is Measurement Techniques it, and thus the RMS voltage, this is an mOH convenient for routine AC voltage As mentioned in the pn:v ious article effective method of measuring a nue measurements. Analog meters of this ryp" on DC Meters (VTV Issue #3) any volt RMS voltagc, regardless of waveform. will have decibel (db) scales, but these meter, mcluding an AC voltmeter, will How<.-ver, the thermocouple is delicate will be compressed at low readings. Since load down the circuit being tested. and the DC output voltage is very small, so much of the measurements in audio However, in addition to the DC resis r�quiring special DC amplification tech revolve around logarithmic db readings, tance, AC measurements are affected by nIques. having a scale where db are displayed lin the shunt capacitance of the meter. The early can be quite convenient. Older shunting effect of DC resistance is to The other scheme for measuring RMS meters of this IYpe used special meter give a lower than expected reading at all voltage is to synthesize the root-mean movements (0 do this logarithmic conver frequencies, while the shunting cffeCl of square, either by analog multipliers and sion. Newer meters either used logarith- meter capacitance is ro cause the reading dividers or by digitizing the waveform VACUUM TUBE VALLEY • A U 0 o T EST BEN C H A C METERS m�ters was a lintar logarithmic scale. The most common model. the 300 (figure 2, page 34), looks a lot older than it really is, and makes a good romine meter. although is nor as sensiti\'e as other models. In 1954 Hewleu+Packard brought out the model 400 (figure 3, page 34) probably one of the best-known audio voltmeters ever. This model was continued through various versions until 1965. when it was superseded by the solid·state model 400E. Tube-type uue RM S voltmeters were made by various manufacturers, including Ballantine and John Fluke Mrg. Older tube+type AC meters can be quile competitive with newer models, often at a much lower cost. The analog meters can be more convenienr 10 use than digital ones when tweaking for a to decrease with increasing frequency. accounted for. RG-58/U (or any 52 ohm peak or a null signal. The standard precau coax cable) has a capacitance of 29 pF per tions for bringing up old tube equipment To give an idea of how much capaci foot (95 pF per meter). which can be a apply for these meters: test the tubes. re tance is a problem, let's look at three dif significant load. Open wire can have form the fi[tcr capacitors, and check for fe rem situations: measuring the signal on lower capacitance, but is susceptible to coupling capacitor leakage. Since these the plate of a low-level driver stage, rhe hum pick-up. A low-capacitance auenua meters have very sensitive amplifiers. noise signal on a 60G-ohm line output stage, lOr probe (to be described in detail in an and microphonics in the first or second and the signal on an a-ohm speaker out upcoming article on oscilloscopes) can amplifying stages can be a problem. It will put. In each case, the shUn! capacitance is reduce the capacitive loading to about 5 often be necessary to try Out lots of tubes treated as a capacitive reactance (Xc), and lO 10 pF, at the cOst of a loss of signal or swap tubes around within a unit to find the vohage divider equation is used [0 level. These probes are only accurate if . qUIet ones. calculate. the voltage drop. If the error is matched to thc resistive and capacitive low, say I %, then Xc =� 100 Rs. Working load of the meter, and need to be careful Wrap-up backwards, (he capacitam;e is derived Iy adjusted. For the ultimate in low+ A good, sensitive AC meter is an essen from Xc by the equation Xc:J /2nfC, capacitive measurements, an active probe, lial art of anyone's test bench if they plan where f is the signal frequency. typically usinf;: an FET right in the probe, p to do serious audio work. A stand-alone with a "guard signal surrounding the For the low-level stage, if rhe plate AC meter, as described in Ihis article, can input lead can be used, resulting in a resistance of the driver stage is 50K and suit this need, or a meter that is pan of a capacirance of as low as 1 pE However, the plate resistor itself is lOOK, then the distortion analyzer (to be described in a active probes arc expensive. and are sel SOUfce impedance is 50K lOOK or 33K. future issue) could also be used. However, 11 dom needed for routine audio measure For the line-level measurement, a source to make [he meter Truly useful, a knowl metHS. impedance of 600 is assumed. For the edge of the limitations and applications of speaker test, if the damping factor is .1, Classic AC Meters AC meters - RMS vs average reading and thell the effe<:tive source impedance is the effects of meter loading - is also need Sensitive meters d�signed specifically 8·0.1 or 0.8 ohms. The fo llowing table ,d. for audio applications became available summarizes the shunt Xc and C required just before World War [I. One of the to create a I % error in the AC measure In the next Audio Test Bench: Signal most popular was the Ihllantine series of ment at 20 Khz: Gmertltors AC meters. A hallmark of the Ballantine Source Xc for C" Impedance 1% drop 20 KHz VTV Renewal or Subscription Form (Photocopy form) 33K 3.3Meg 2.4pr Yes, I want to subscribe__ renew __ to VTV Number of Yeo rs_ _ GOOn -,-- -:-: 60K 132pF S32/yr four issues US, S40/yr Canada and $45/yr Asia, Europe and Wo rld. 0.8n 80<> O.lflF Cash, US Bank Check, Money Order or Credit Cords (after 7/96) As can be seen, an extrerndy low Vacuum Tube Va/le , 1095 E. Duane Sfe. 106, Sunnyvale, CA 94086 (408) 733·6146 capacitance is needed for decent measure menu; at 20KHz for the plate measure NAME ______ment. Even for a 600 ohm iine, a pretty ADDRESS ______low capacitance is needed. Only on the _ CITY ______speaker load would average load capaci STATE ______{ance not be a problem. COUNTRY ______MAIL CODE/ZIP ------ Typical AC voltmeters have an input CREDIT CARD TYPE ______capacitance of 15 pE However, rhe capac CREDIT CARD NUMBER ______EXP. DATt-E__ __ itance of the test lead needs 10 be AMOUNT ENCLOSED VACUUM TUB E VALLEY • V A C U U M TUB E VALLEY - GO AHEAD Have You Been Wondering Ask fop engineers and music lovers worldwide whot Which Tubes Sound The Best? capacitor they choose for /heir ulNmofe designs. -----IK--0--V L A N D---- Then You Need This Report! MUSICAP" The most naturally revealing capacitor, Film and fall Eric Harbour of Glass Audio and Vacuum Tube Valley. po/ypropyfene construction - optimlzed fOl fine speakers recently tested more than 1000 audio tubes-both \'intage and vacuum tube electronics. Precision made In fflau.s.A. NOS and current production. 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