GA-40 Les Paul Amp help needed

All,

I just picked up a '56 Gibson GA-40 Amp. It was a basket case but the price was right (cheap!). Channel one is OK but not all that loud. The second channel with Tremolo does not work and it needs a bit of cabinet repair. Looks all original inside. I do not see very much technical info on the web for these. I have the schematic but it does not match the input section. If anyone here has info or knowledge that could help in getting this sorted out and running I would appreciate the help. I will need a 6SQ7 for sure as this one is dead. Zero output on BK707 for all 3 tests. Stone cold after 1 hr. plugged in so filliment must be gone. I tried a NOS 6SR7 I had but it did not fix problem. I have heard this is common on these and a bunch of caps will need to be changed.

I may want to re-cover the cab after repair of broken parts. Anybody got a clue as to where you can buy the covering they used?

Thanks in advance for the help.

Mark

Bunch of Fenders and Guilds.
And a few busted amps.

Hi Mark, welcome to LTG and congratulations on your GA40.

Tremolo; Do you have 6.3VAC at either pin 7 or 8 of the 6SQ7 socket? The filament is fed off one side of the heater winding; hot on one side, connected to ground on the other. The more common trem failure is in the cluster of trem caps that are - I think in your amp - inconveniently mounted on the underside of the circuit board. If so and to get at them, you'll have to loosen all the controls and jacks from the faceplate, drop them out into the chassis, undo the hold-down nut/s on the standoff/s and flip the board over. Like this - the yellow cap and the two bumblebees to its right are the trem caps (GA20T pictured);




Anyway, confirm or fix heater voltage and clean controls and footswitch; if you don't have any trem, then it's in the oscillator circuit.

Tolex; is your amp brown over tan or the later maroon over grey? Not sure that he'll sell to you but try Rob at Buffalo Amps; boutique that specializes in rehabbing Gibson amps.

Hope you get it running correctly. CJ