jkchrome Posted February 26, 2011 Share Posted February 26, 2011 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. Quote Link to comment Share on other sites More sharing options...
L5Larry Posted February 26, 2011 Share Posted February 26, 2011 I have schematics for the GA-77 and GA-77RVT, but NOT the GA-77RV, sorry. Aspen Pittman of Groove Tubes seems to have one of the largest schematic collections around. I would try to contact him, or Groove Tubes, for the information. That last time I talked to him I reached him at 1-800-459-5687. Quote Link to comment Share on other sites More sharing options...
jkchrome Posted February 27, 2011 Author Share Posted February 27, 2011 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. Quote Link to comment Share on other sites More sharing options...
Grog Posted February 27, 2011 Share Posted February 27, 2011 I have an original copy of the "Gibson Amplifier Master Service Manual". It doesn't list a GA-77RV. The GA-77 looks to be from 1953-54. I have infor on GA-77, the two versions of the GA-77RET and GA-77RVT. I have a later version of a GA-77 RET with the Tel-Ray Oilcan Reverb & 15" JBL. Quote Link to comment Share on other sites More sharing options...
jkchrome Posted February 27, 2011 Author Share Posted February 27, 2011 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. Quote Link to comment Share on other sites More sharing options...
jkchrome Posted March 12, 2011 Author Share Posted March 12, 2011 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. Quote Link to comment Share on other sites More sharing options...
BobB Posted March 13, 2011 Share Posted March 13, 2011 check www.schematicheaven.com for free tube amp schematics. www.musicparts.com has many schematics available, but there is a small charge to get a copy from them. www.tubesandmore.com is a great place to find supplies for restoring vintage amps. Quote Link to comment Share on other sites More sharing options...
jkchrome Posted March 16, 2011 Author Share Posted March 16, 2011 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. Quote Link to comment Share on other sites More sharing options...
Dlaltick Posted April 1, 2021 Share Posted April 1, 2021 I have a Gibson ga-77rv and if it were 6eu7’s it has been changed to 12’s tube compliment is from v1 to v8 12ax7, 12ax7, 12au7, 12ax7, 12au7,6l6,6l6,5ar4 hope this helps, great sounding amp that never saw mass production Dustin Quote Link to comment Share on other sites More sharing options...
PDH Posted May 1, 2021 Share Posted May 1, 2021 (edited) 3- 6eu7- 1 -12au7a 2-6l6gc 1- 5ar4 Edited May 1, 2021 by PDH Quote Link to comment Share on other sites More sharing options...
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