- VACUUM TUBE VALLEY. Issue 7 published Quorrerly Spring/Summer 1997 Celebrating the History and Quality of Vacuum Tube Technology Price S8.00 The 6DJ8 and other Frame Grid Tubes V.cuum Tu".Computen The Savage Art al.-Tlm. Th ...... Sou.d A'tee Lansing Pov#erhouse . Th. P.ter ...... .to ry Early Sound Amplification __ Ien.en ELECTRO-OYNAMIC SPEAKERS .�" EDI TOR S P AGE AND INDUSTRY NEW S NewTube!i from S.-etlana VTV Issue # 7 $vedana Elecuon Devices has recently intro­ Table of Contents: duc",d their version of the EF8G. Thi� TUbe k:l.ture� low noise, high gain, internal shield­ All About the 60J8 and Other ing and gives exrTcmciy low dislOrrion in Frame Grid Tubes .......... 3 either pcmode or triode conneccion. Retail price of the EF8G is S 14 US. listening to the 60J8 .8 VIV recei,'� pre-producrion wnp les of vetlana's SV6L6GC, which is a very dose: Oscilloscopes· Part 10 S 2 copy of the original Sylvania 6L6GC/STR387. These tubes work very well in guirar :unps, 13 A/tee1500 Series both new :and vimage. 50nically, they :Ire sim­ ilar to the original RCA 6L6GC blackpb.lcs The Great Voice - Peter Jensen 18 and the STR387 Sylnnias.Retail price is 518 US for single tubes and 524 each in marched Build A Comparison Preamp .. 24 pairs or quads. L�rgc qU:l.milies of Ihis tube will be availabk in I.m, 1997. Antique Sound Lob .. 26 Swriallll AQ-l 002 Svedana has �ho introductd :;I.n amazing power triodt. The new 3CXJOOAI looks like 3008 Tubes ......28 Computing With a lran�mit!ing tube, but is actually a low-mu audio.The OESKB is an affordabk trans­ audio triodt. Pbte diuiJnlion is 300 W.U1S 3 former with a 5000-ohm primary, inltndtd to Ceramic Capacitors . and plate rcsisrana is 4}O ohms. It is an 1 match tubes such as 45, 50, SV811-3, 300B exttrnalanode typeand requirc:s fOruG-air and the likt, running up 10 65 mA pblt cur­ Computer Video Review . .. , 32 cooling. If driven correctly, in Cl:lS$I, AB a .tnt. The similar TM3KB has a 3000-ohm pair of Iho:sc: tubes would produce more than primary, intended for a single 2A3, 6B4G or VTV at CES .34 400 wam! 1997 300B running at up to 70 mA. Bandwidth of Pre-produetion samples of the long awaiTed both types is 18 ]'h 1040 kHz, _I dB, with Tube Dumpster ..36 - 417A/5842 Svedana version of the 3000 power rriode maximum power raring of 10 waItS and with werc received by vrv for evaluation.The output apabiJides for 2-ohm through 16-ohm tube is well made, with heavy glass and inter­ spt'akers. nal components thal appear idential to the Fo ••e allr big po�r, the Electr;J.-P.int original item. It is clearlysuperior 10 the OTher KJ..IOKB is a J>C'rfect match for a single lcss-expcnsi\'e 300B5 on the market. [t has SV572, 211 or 845, In 10k-ohm primary and greot bass, extended high frequency response 3O-w:m r;J.ting go along with a bandwidth of and is extremely music..1.The $\'tTlana 300B 19 Hx to 24 kHz at -I dB--world-c!:lS$J>C' rfor­ will not be available umil lare 1997. Price has mance for such a high primary impedance. not been determined yet. For more informa­ ti on, contact: Svetlana Electronic Devices, And finaU)" Eleclr;J.-Prim has inrtTSnge 8200 Memorial Parkwar, J-\untsviHe, Alabama transformers for SE and push-pull applica­ 35802, FAX 205-880-8077, Phone 205-882- tions. The 3533-2 has a primary of 8.5 1344. KOhms and a 1:1 ratio. The primary can han­ dle up to 20 mA of DC plate eurrem.For Electra-Print Introduces New push-pull, the 3634-P has a 9k primary and Transformers cemer-tapped secondary, with a 17 mAp rima­ EJeclr;J.-I'rintAudio Co. has stan«l. manu­ ry currem. Contact: Electra-Prim Co., 4117 facture of thre.:: new single-en d«l. OUTpUt Rox.anneD ri"e, l2s V�as NV89108. phone (r;J.nsfonners intended for maximum-quality (702) 396-4909, ru (702) 3%-4910. EDITORIAL STAFF Vacuum Tube Volley is published quarter­ Copyri�t C1997 Vocuum Tube Valley 1.W. ly for electronic enthusiasts interested in the and Big Tone IM All rights reserved. Charles Kittleson - Editor and Publisher colorful post, present and future of vacuum Unauthorized copying or duplication of this tube electronics. John Atwood - Technical Editor publication or any materials within it is strictly forbidden without permission from publisher. Annual subscription (4 issues) is $32/US Eric Barbour • StaffEditor $40/Canodo, $SO/Europe $60 Asia. Send circulation and editorial correspon­ Terry Buddingh - Guitar Amp Expert Cosh, US Bank check or Credit Cords dence to: Vacuum Tube Valley ore accepted as payment. Sieve Porr - Art Diredof Phone/FAX 408-733-6146 1095 E. Ouone Ave., Suite 106 Julie P. Werner ·Copy Editor Svnnyvale, CA 94086 USA Web Site: http://www.vocuumtube.tom email ·[email protected] VACUUM TUBE VALLEY ISSUE 7 ALL ABOU T THE 6 D J 8 has to have high uansconducrance; and to use it at UHF or higher frequencies, All About the the tube strucrure has to be small. The limit given for conventional rube manu­ facture is usually the 6AK5 pemode. with 6DJ8 and other a rated rransconductance of 5000 to 5500 pmhos and a grid-plate capacitance of Frame Grid Tubes 0.02 pF. Ra)'theon's GAHG bettered that in 1946. reaching a Gm of 9000 p.mhos By Eric Barbaur © 1997 All Right!. Re�rved with some difficulty. 1. In tro The developmem of the frame grid took place simultaneously on both side:o; In previous issues ofVIV, wc have of the Atlanlic. in 1948-49. Tungsram introduced you to many tubes that arc (UK) engineer John A. Sar rove was the now popular for audio use, and nothing g forgotten British pioneer of this tube but. And we have told you that many of type. He developed the Tungsram UA-55 these popular lypes weren't even intended as a dual-section beam tetrode for audio for the current applications when they power applications. ironically. BUI it was first introduced. So, just to warn wefe apparently a commercial failure. It was you in advance, it's time to do that again. sensitive and was also designed to operate watt on only 90 volts Many audiophiles today swear by the efficiently, giving 1 60J8/6922 dual uiode family. They lend plate power. This was made possible by the dose spacing that frame grids allow. to think of these as the most detailed­ sounding tubes of all. Yet lhal whole technology and design was intended for low-noise RF appliColtions, usually in receiver front ends. Audio was hardly considered until the 19705. These types are consnucted with a complex kind of ri d which was pioneered in 1948, g known as a frame grid. Sophisticated e([uipment is required to make frame grids, whereas the convemional tube grid is juS[a spiral of wire wrapped around twO soft metal POSts. The idea of using frame-grid tubes for hi-fi would have been unthinkable in the early Fifties, but WE 416A Muliard/OM 6DJ8 evemually their technical superiority and common manufacture made them viable for home audio equipment. Special tubes were developed for UHF The credit for the frame grid usually before World War 11; they were usually 2. History goes to J.A. Monon and R.M. R)'der of made as physically small as possible to BeI[ Te lephone Labs. They introduced the reduce capacimnce and parasitic induc­ Unlike the conventional tube grid, the 41GA rriode at the winter 1949 meeting tance, but were nOt outstanding in frame grid is JUSt what it seems. Rather of the AIEL This remarkable (and odd­ transconductance. This family indudes than being wound around a swaged pair looking) metal tube was intended as a the Western Elecuic �doorknob" IUbeS of postS, very fine wire is wound onto a microwave RF amplifier for telephone such as the 316A. 380A thm 387A, 713A rectangular frame of stamped metal, often long-distance relay C<Juipment. The and 717A; RCA's "acorn� serie:o;; and the molybdenum. This gives very consistent extremely fine pitch of the grid wires. 9000 miniature series. Many were used in rid suuctures, which allows the grid (Q g \000 per inch. and their 0.6 mil spacing earl)' FM broadcast receivers and in UHF be laced closer to the cathode, thus p from the planar cathode were records at military radio equipment of rhe war. yielding higher uansconducrance. the time. RCA pushed this as far as it would go with the 6J4 in 1944. a UHF triode with Usually, because the frame grid is nat During this time period, some more con­ Gm-I2,OOO pmho. The 6J4 was not very rather than tubular, a pair of grids must ventional-style miniature glass tubes were successful. It ap arently was vcr)' difficult be used for a triode, with onc being introduced b), Bell Labs and manufac­ p to make. and a h i gh infant-mortality rate placed on each side of the cathode. A tured by Western Electric. Besides the may have been the reason for the high teuode requires four frames. a pentode 41GA. WE also produced the 404A pen­ price of 58.35. Imagine paying 5100 six. Many meta[/ceramic tubes intended tode.