Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: cgiesel1 on August 24, 2012, 09:18:37 am
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Hello All,
I am a bit of a newbie so it is possible the answer to my question is somewhere in this forum though I did a search on 6V6 and 6V6GT and did not see anything related. I also looked at the 'Sylvania Tube Substitution' .pdf with no luck.
I am rebuilding a tube amp that currently has four Magnavox 6V6GT tubes. The Hoffman catalog only has EH6V6 tubes. Am I correct that the 'GT' references the packaging style only --i.e. the glass surrounding the tube-- and all of the other characteristics are the same/similar?
In short, can I use EH 6V6 tubes as replacements for my 6V6GT tubes?
Thanks,
Chris Giesel
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In short, can I use EH 6V6 tubes as replacements for my 6V6GT tubes?
Yup. The attached datasheet says they can handle 450v on the plates and have a max dissipation of 14W, which are actually higher max specs than NOS (new old stock) 6V6GTs (see 2nd attached datasheet). So theoretically you can drop them in wherever you'd use a GT and have them work.
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thelonious,
Thanks for the reply.
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Note also that most modern tube makers/vendors add various extra letters to a tube type # which really only signify variants that have meaning with respect to that particular manufacturer. In this case, "EH" just means Electro-Harmonix is the vendor of the tube.
Through the 70's, American tube types used a letter/number combination which gave some information about the tube's features.
- The first digit indicates the filament voltage ("6" = 6.3v filament)
- Letter(s) assigned sequentially with each new tube type registered. These ascended from "A" for most types, while rectifier descend from "Z". In rare instances, some double-letter combinations have specific meaning (we won't confuse things by covering those here).
- A number to indicate the "number of useful elements" brought out through the pins. For a pentode, you might see a "5" or a "6" to indicate 5 internal elements plus a cathode; sometimes, the internally-connected supressor grid is not counted among the useful elements.
This numbering usually results in the actual number for the prototype version of the tube. Old 6V6's were indeed labeled "6V6" and came in metal envelopes. Later versions switched to a sloped-shoulder glass envelope, and were designated "6V6G". The "G" indicated the new glass envelope. Even later, the shape of the glass was changed to a straight-sided glass tubular envelope, and then termed "6V6GT". "GT" indicates "glass-tubular".
Additional changes might be made to a particular tube. A low-loss micanol base might be used on the GT version to yield a 6V6GTY. There were also 6V6GTA's which actually had a plate with a higher dissipation rating. However, the addition of A's and B's really only tells you there was a change; you should consult the data sheet to find out what that change was.
But as I said, modern vendors slap all sorts of extra letters on their tubes which don't conform to the old system. For example Groove Tubes makes (or used to make) a 6L6GC which they state was produced on tooling from a defunct G.E. plant. Therefore they call this tube a GT-6L6GE, to indicate "Groove Tubes, 6L6 G.E.-style".