IARCHS NEWS – Winter 2006

Auction Action! I RCHS Iowa Antique Radio Club and Historical Society IARCHS NEWS – Winter 2006 Boy talk about “pay backs” no sooner did I the scope of his contributions over a long mention in the fall newsletter how warm it career. We also have in this issue an had been than we get clobbered with a interesting tech article on the variety of record breaking Decemberrrr. I think I’ll 6SN7 tubes that was pointed out to me by avoid comment on the current weather other Tom Laszynski, the newsletter editor for than to note that I sure am glad winter got OKVRC. here because I couldn’t take too much more of fall. BUT before the weather turned, a Dave Perkins few of us were able to make it to an auction to stock up on “good stuff” (more pictures to come). Also in this issue are plans for a The Lowdown on the Lowly 6SN7 “hands on” basic electrical restoration In the last couple OKVRC newsletters session at the home of one of our newest there has been an interesting series of members, Bob Elbert of Roland, and yet articles on tubes. In an email exchange another fine contribution from Sherry with Tom Laszynski regarding these I Cowden of OKVRC; a tribute to the career learned of an interesting web site that of Ralph Edwards that she originally includes write ups on some common published just a few weeks before he died. I tubes that delineate the features and suspect many of you will recall Mr. differences within their respective tube Edwards’ association with “This is your families. What follows is an example Life” as I did, but I bet you’ll be surprised at that is not only technically interesting but 1 it may also lead you to find some two triangular shaped plates facing each “hidden gems” in your stock of tubes. other mounted high in the tube, with either a Credit for this is due to Brent Jessee top or bottom getter. The early Sylvania Recording and Supply Inc. and more types had a top getter and silver flashed the can be found at www.audiotubes.com . entire top of the tube, sometimes called "chrome tops". Many brands used this The 6SN7 tube is a medium-mu twin triode design, but the high mounted triangular in an octal based package, usually glass, plates means it most likely was made by although some metal envelope types were Sylvania. The early RCA "GT" types were made. In normal use it operates as a class A usually in either a medium or short envelope amplifier. It was widely used in the early and have a grey RF shield sprayed on inside days of television as the vertical amplifier, the glass. The GE and KenRad types were and it's use was so common in most TV similar, but the inner glass coating is deep chassis designs that vintage 6SN7 tubes are black. These tubes usually have flat black still fairly easy to find today. Audio plates, like large 12AX7 blackplates. The designers soon found it made a great audio military versions of these are the VT-231 preamp with it's large plates, ample power and are in very high demand today. reserve, and low microphonic octal package. The GTA and GTB types, having been fine 6SN7GTA / GTB: tuned for demands in television chassis This is the later improved version, and the vertical sweep circuits, can handle up to 7 improvements were primarily geared toward watts maximum plate power! the TV chassis designers who demanded more max. plate wattage and voltage, where The demands for these tubes today are vertical circuits can put up to 1500 volt primarily in vintage and recent design audio pulses at 7 watts on the plates. For hi-fi amplifiers and preamplifiers of the high- audio use, these improvements are fidelity type, up to and including the most meaningless. These are fine tubes, expensive and esoteric. It seems there is a nonetheless. Most are found in the short 6SN7 tube for every taste and budget, and glass envelope, but some brands like some of the vintage versions are being Raytheon used the Tall Boy style. Sylvania hunted to extinction, especially those made made tubes have the triangular plates for the military. I will try to explain the mounted lower, and set at angles to each differences between some of these tubes, other, although some of the very earliest and list specifically what I have in stock. I examples of the GTA types still used the expect some of these tubes will skyrocket in dull blackplates facing each other. RCA price worldwide as more and more audio used the flat black plates "sideways" to each designers find out that this preamp tube is a other, and GE used the grey plates parallel design that really can't be improved to each other. The Sylvania types in demand upon....and that the fine vintage tubes just have a large top getter patch. The earliest cannot (and probably will not) ever be Sylvania GTA types have a green label and duplicated by a current production tube. heavy top getter flashing extending down Three envelope sizes are common in the full the sides of the tube. The early GTB types octal base version: SHORT, glass is 1.5 are similar, but have a yellow or red label. inches high; MEDIUM, glass is 1 3/4 inches The versions from the 1960s have the getter high; TALL or "TALL BOY", glass is 2 just covering the top of the tube. All of these inches high. have the same black triangular plates and are excellent tubes. The GE types have a side 6SN7GT / G: getter and large parallel grey plates, and the RCA used both bottom or side getter. Most This is the original version of this tube. It other vintage USA brands you find will have may be found in all three sizes of glass been made by these three vendors, and will envelope. The Sylvania Tall Boy types have be one of the above variations, regardless of 2 brand on the label. A few were made with with brands like Cossor, Marconi, Osram, brown micanol bases, the RCA types being Mullard and Brimar are awesome. They are very dark brown, the GE types being a noted for their excellent sonics in audio use. lighter, marbled brown. Many audiophiles Some may be labeled with either ECC32, prefer either the Sylvania chrome tops, the ECC33, 6SN7GT, or a combination of these. RCA, or the GE side getter over any others, Some have the BVA label, and the older even over the military or redbase types. versions often have the date and factory These are all a great bargain now, and are codes on the bottom of the base between the sure to be rare and expensive tomorrow. pins. Be careful when buying these! Later versions were made in Russia, but still say 6SN7W / WGT / WGTA: "Great Britain" on them! The Russian tubes This type indicates a military spec tube that have a rounded glass top, and a cup or was not made for consumer use. These square shape solid getter. They also often usually have extra support posts on the plate have a large, very shiny black base NOT structure, heavy mica spacers, and brown made from bakelite but from an inferior micanol bases. These also have the famous plastic. We do not carry these types in our triangular shaped black plates. They have stock. been ruggedized to withstand shock, the brown low loss micanol base resists mold, CV1988: mildew, and fungus growth, and they can Another fine military version of the withstand heat even if used upside down. 6SN7GT, this time from Western Europe. The early Sylvania 6SN7W types from the These don't often turn up in the USA. The 1940s had a metal collar around the base, few I have seen have been British and then later a black base. These look internally manufactured by Mullard. This tube is alot like the early Sylvania GTA types listed usually medium glass, dark brown full octal above. Sylvania made these for other brands base, and has a dark grey inner glass coating as well, including RCA. Easy to spot as they which hides the plates from view. I suspect have the triangular blackplates facing each these are cylindrical plates, as most of the other in a short bottle, with a very heavy European 6SN7 varieties have been this chrome top flashing extending down the type. These are rare, and worth seeking out. sides of the tube. These are RARE and Not only do they sound as good as the best worth seeking out! The WGT and WGTA industrial 5692, but they have the higher types all had brown bases. Only the WGTA specs of a 6SN7GTB with regards to plate types made in the late 70s and 80s reverted current and voltage, and have the long heater back to black bases then coin or wafer bases. life and overall ruggedness of the US These are all wonderful tubes, are long military types. A winning combination! lived, and sound fantastic. No wonder they are fast disappearing from the vintage 5692: market. This is the premium commercial / "industrial" grade of 6SN7. The most ECC32 and ECC33: famous of these are the RCA "redbase" A fine European version of the 6SN7GT. series, with their distinctive red marbled full These don't often turn up in the USA. The octal bases. These are always in the short few I have seen have been British and glass envelope style, and most have four manufactured by Mullard or Brimar.

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