I bought this amp last summer ... just now getting it on the bench; 1960-1962 Gibson GA30RV 'Invader'; two channels, 3X6EU7 including reverb drive and recovery and 12AU7 phase inverter/driver, 2X6V6, and 5Y3 rectifier, 12" Jensen P12R and 8" C8S. On paper, with its 6V6s and cathode-bias, the amp is similar to a cross between a Fender 6V6 Super 5E4 with fixed-bias and a Fender 6L6 5E5A Pro w/ cathode bias but without Fender's better-grade transformers and cleaner phase inverter.
In the darker/later Gibson tweed:
Predecessor model:
Successor model; fitted w/ Jensen P10R and C12R speakers:
Chassis view; re-capped and new power cord within the last few years but didn't bother with the preamp cathode bypass caps:
Bonus! Speakers were recently reconed. Magnet on P12R measures 2.75" sq., period-correct if not necessarily original. The chatroom buzz on these is that the 8" speaker with it's smaller voice coil, breaks up before 12" speaker. Since it isn't reverb-specific like a Guild, chances are that I'd just leave it disconnected before I'd replace it:
Reverb can w/ hold-down on left and split lower baffle batten in left-center. Cabinet also used for models like the relatively uncommon GA40LP/15". I'll do something like this to the GA20T to allow the speaker and bell to sit lower in the cabinet. Note footswitch; typical block of mahogany ... this one used as doggie chew-toy:
The amp presented with a dull, constipated tone, a 'presence/hum' thing in the 12" speaker ... as though it were going to jump out of the cabinet, and channel 2 has noticeably less volume than channel 1. Seller said that he switched wiring from former daisy-chain config back to design. It's also possible that since the reverb lives on channel 2, it would never have the same volume. I have the amp apart to confirm the un-do of the 'daisy-chain' - potential source of volume imbalance - and general maintenance.
In another forum, a poster suggested that the tone problem may have to do with the possibility of the voice coils having been replaced along with the cones but not put back in original polarity; that is, if/when speakers went back in cabinet and the vcs were reversed, then hooking it up as it had been would result in either/both speakers being out of phase. And, they look new enough that they may not have much play time on them to loosen up the cones. With the speakers out, I can confirm + and -, mark them, and they will be right on the go-back-in.
The several National (Yugoslavian) 6EU7s will be replaced by NOS GEs, a NOS Brimar 12AU7 for the phase inverter, a pair of NOS TungSol 7408 6V6-equivalents, and a mil-spec 6087/5Y3 for the rectifier. If a premium tube set, circuit checks, and confirmed speaker polarity don't do it, then I'll probably replace the output transformer. In one sense, I don't care what it sounds like ... so long as I think it sounds as good as it can.
In the darker/later Gibson tweed:
Predecessor model:
Successor model; fitted w/ Jensen P10R and C12R speakers:
Chassis view; re-capped and new power cord within the last few years but didn't bother with the preamp cathode bypass caps:
Bonus! Speakers were recently reconed. Magnet on P12R measures 2.75" sq., period-correct if not necessarily original. The chatroom buzz on these is that the 8" speaker with it's smaller voice coil, breaks up before 12" speaker. Since it isn't reverb-specific like a Guild, chances are that I'd just leave it disconnected before I'd replace it:
Reverb can w/ hold-down on left and split lower baffle batten in left-center. Cabinet also used for models like the relatively uncommon GA40LP/15". I'll do something like this to the GA20T to allow the speaker and bell to sit lower in the cabinet. Note footswitch; typical block of mahogany ... this one used as doggie chew-toy:
The amp presented with a dull, constipated tone, a 'presence/hum' thing in the 12" speaker ... as though it were going to jump out of the cabinet, and channel 2 has noticeably less volume than channel 1. Seller said that he switched wiring from former daisy-chain config back to design. It's also possible that since the reverb lives on channel 2, it would never have the same volume. I have the amp apart to confirm the un-do of the 'daisy-chain' - potential source of volume imbalance - and general maintenance.
In another forum, a poster suggested that the tone problem may have to do with the possibility of the voice coils having been replaced along with the cones but not put back in original polarity; that is, if/when speakers went back in cabinet and the vcs were reversed, then hooking it up as it had been would result in either/both speakers being out of phase. And, they look new enough that they may not have much play time on them to loosen up the cones. With the speakers out, I can confirm + and -, mark them, and they will be right on the go-back-in.
The several National (Yugoslavian) 6EU7s will be replaced by NOS GEs, a NOS Brimar 12AU7 for the phase inverter, a pair of NOS TungSol 7408 6V6-equivalents, and a mil-spec 6087/5Y3 for the rectifier. If a premium tube set, circuit checks, and confirmed speaker polarity don't do it, then I'll probably replace the output transformer. In one sense, I don't care what it sounds like ... so long as I think it sounds as good as it can.