jkchrome

Hi, Thanks for all suggestions. I had my amp tech (very experienced) look at it and he discovered that all the preamp tubes are wired for 12ax7 and driver is probably a 12AU7 or 12AT7. He thinks it may have had the preamp tube sockets rewired from what would have been 6EU7 tubes. The amp has definitely seen some modification from stock. Anyway, it's cool and now I can actually stick something in and run it, and not blow the 6eu7 tubes that I bought based on the one schematic I did find.

Hi everyone, Well, since I started the post I contacted Gibson support (sent a schematic for a different amp), contacted Groove Tubes as suggested(got a reply, no schematic), contacted Skip Simmons who has worked on other oddball Gibson amps for me (his suggestion was to have someone that knows look at the pin wiring to determine tubes, and that's a good idea so I'm having that done now by my regular amp tech that has been working on amps for about 40 years). Meanwhile, if anybody has an 8 tube version like mine, I'd love to hear from you. And I will post the results of getting it looked at once I hear back.

Thanks. It's possible that a schematic for this model doesn't exist , they apparently made around 300 or so of this reverb/non-trem model , only for one year, and not the same amp as the earlier GA77 or the later, oil can ones)), and I even have a schematic with GA77RV on it but a slightly different tube setup. I'm hoping that mine isn't the only one out there with 8 tubes. Maybe someone out there will recollect seeing one.

Thanks. I'll try that. So far I think that I have the first three right, 6EU7, and the inverter, 12AU7, 6l6 pair and GZ34. But, the mystery is what tube is in between the last 6EU7 and the 12AU7. If I knew that I'd be at least able to get started. I'm hoping somebody out there can fill in this gap. Apparently Gibson put out two variations (at least) of this short-lived amp. Seems like mine must be the less common one. The amp does not look like it's been modified. I actually have a GA77RV schematic that I found BUT with only 7 tubes. pretty frustrating. Worst part is that I owned the amp briefly, with tubes in it, and sold it right away to the person that just sold it back to me, but in the meantime he pulled out the tubes and has no recollection of what was there.

HI I have a 1961(?not sure of year) tweed GA-77RV (has reverb, no tremelo). I bought it years ago and am finally getting around to trying to get it running. Unfortunately I don't have a tube chart and the only schematic (downloaded online) for this model I have found shows 7 tubes, but my amp calls for 8 (five small tubes, two power, one rectifier, and the power and rectifier are octal sockets, pretty sure this had 6L6 power tubes and maybe a 5AR4 but just guessing). The older GA77 is of course a different amp. When I got it, some tubes were missing so I need to figure out at least the proper tube lineup and order before I try to do anything else. The amp serial number starts with an 8, it's a tweed amp, and the 15" Jensen has a 1961 date which I think is the year of this amp. Any ideas? Thanks in advance.