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previous: Troy I've got a friend's GA-5T right now... -- 9/15/1999 5:11 PM

Re: GA-5T Different Tubes

9/17/1999 3:45 PM
Doc	Re: GA-5T Different Tubes The 6EU7 is really a 12AX7 (with dedicated 6v heater) with a different pinout. It's set up with a tube basing for minimum hum pickup, because the heater wiring doesn't have to cross over the signal wiring. It's also supposed to be a low-microphonic device, but I've found quite a few that weren't. The 6C4 is a 7-pin single triode, internally it is 1/2 of a 12AU7. Actually, the 12AU7 has two 6C4 structures inside. Both of these tube types (6EU7 & 6C4) are still rather plentiful and reasonably priced today. I'm just giving the substitution info if you ever want to, or need to, convert to currently manufactured types. If this amp were mine, I'd go ahead and replace all the capacitors and see how it sounds. You could tweak some of the tone control circuit or replace a tired speaker, but there's probably no need to do any major mods. Chances are it will sound pretty damned good. Many of these small Gibson amps are revered by folks who play harp or slide guitar, and judging by what some kooks are asking for them at guitar shows, getting rather scarce.

9/17/1999 3:45 PM

Doc

Re: GA-5T Different Tubes

The 6EU7 is really a 12AX7 (with dedicated 6v heater) with a different pinout. It's set up with a tube basing for minimum hum pickup, because the heater wiring doesn't have to cross over the signal wiring. It's also supposed to be a low-microphonic device, but I've found quite a few that weren't. The 6C4 is a 7-pin single triode, internally it is 1/2 of a 12AU7. Actually, the 12AU7 has two 6C4 structures inside. Both of these tube types (6EU7 & 6C4) are still rather plentiful and reasonably priced today. I'm just giving the substitution info if you ever want to, or need to, convert to currently manufactured types.

If this amp were mine, I'd go ahead and replace all the capacitors and see how it sounds. You could tweak some of the tone control circuit or replace a tired speaker, but there's probably no need to do any major mods. Chances are it will sound pretty damned good. Many of these small Gibson amps are revered by folks who play harp or slide guitar, and judging by what some kooks are asking for them at guitar shows, getting rather scarce.