Tube nomenclature

I dont know about a 6sn7g .... that may have been a misprint or a very limited production version. There is the original 6sn7gt which can take 300 volts max on the plate. The 6sn7gta was the first revision of the 6sn7 allowing the tube to accept 450 volts max on the plate ...... while the last revision, the 6sn7gtb, added a warmup delay, in addition to handling 450 volts max on the plate. All these tubes use the same octal tube base. The 6sn7gta/b can work in any 6sn7 circuit, while the 6sn7gt will not work in circuits optimized for the higher voltage handling capabilities of the 6sn7gta/b. The 6sn7gt is limited by the amount of plate voltage, again, that is 300 volts.

There are definite sound quality differences with the older 6sn7gt generally being considered the best sounding version. The 6sn7gt is a more detailed, airy and spacious sounding tube. Why? The changes made to allow the 6sn7gta/b to handle higher voltages increased these tubes internal capacitance ..... which deteriorated the tubes sound quality for audio use. The 6sn7gta/b were optimized for use in TV sets.

I dont know of a table for conversions but there are only a few Russian 6sn7's in current production. The Elecrto Harmonix (EH) 6SN7, EH 6SN7 "gold pin" and the Sovtek 6sn7. IMO, none of these tubes sounds as good as the nos 6sn7gt. I would also take most 6sn7gta/b's over the Russian tubes as well .... the only exception being the RCA 6sn7gta/b because I dont like darker RCA house sound. The "gold pin' is my favorite of the three Russian tubes.

Be aware the 6sn7gt was made by GE, Hytron, Ken Rad, National Union, RCA, Raytheon, Sylvania and Tung Sol .... and these brands all sound different. Also, be aware the 6sn7gt's tubes changed construction over the years and each brand may have several types. For example, Tung Sol ..... 1) 6sn7gt black glass roundplate (both short and medium bottle size) 2) 6sn7gt clear glass gray plate 3) 6sn7gt clear glass gray plate, "mouse ear' 4) 6sn7gt clear glass, tall bottle, chrome top. Finally, be aware there are military versions of the tubes 6sn7w, 6sn7wgt, 6sn7wgta (usually sylvania tubes .... but not always) and the original 6sn7gt can be referred to by its military name the vt-231.

To add further confusion ..... tubes were rebranded by Motorola, Standard, Philco, Westinghouse etc.... and these tube can be from any of the eight manufactures I mentioned above. In fact, I have a Tung Sol black glass round plate that is branded a RCA vt-231. Rebranding was a commom practice for tube manufactueres to meet order quotas and can make tube identification a daunting proposition.

For research, here is the best guide I have come across .....

http://www6.head-fi.org/forums/showthread.php?t=121357

That's what I felt like a month ago while trying to learn about tubes. And yet now I can completely understood all of sacdlover's post.

It's quite a good, concise explanation of the 6SN7 and general tube info, though.

Don't forget the 6SN7 (the original), 6SN7A or 6SN7W, or the 6SN7WGT and 6SN7WGTA, or even the 6SN7GTY...