I built this amp myself and overall it has been a successful endeavor but it still has one nagging problem that has me pulling my hair out. There's a lot to this amp because its a blend of the ab763 power section and a 6G8 tone stack. It has also has switchable OP trannies with a cathode lift switch to take 2 tubes out. The reverb and vibrato section are all std ab763 twin. All the trannys are Mercury Magnetics.
All of that stuff works fine but I have a problem with the reverb channel. If I play it where it starts to get loud it sounds like a blown speaker. Also the reverb is always on even if the foot switch is disconnected (I can turn it off with the knob). The foot switch used to work and the jack wiring looks fine.
The normal channel is fine and I can crank it all the way up. It seems to me that this problem has crept up on me and maybe I caused it by having it on without the reverb tank connected (while bench testing, ect). The only thing that makes sense to me is maybe I've damaged the reverb tranny??
I'm at my wits end! Tried different tubes, voltages are all good, disconnected the vibrato circuit from the driver circuit and gone over the circuit many times.
I guess the next thing I could try is to bypass both the reverb and vibrato circuits to isolate the tone stack.
If anyone has any Ideas please help. I'm leaning to try a reverb trans.
Thanks and here's a few pics of it.
All of that stuff works fine but I have a problem with the reverb channel. If I play it where it starts to get loud it sounds like a blown speaker. Also the reverb is always on even if the foot switch is disconnected (I can turn it off with the knob). The foot switch used to work and the jack wiring looks fine.
The normal channel is fine and I can crank it all the way up. It seems to me that this problem has crept up on me and maybe I caused it by having it on without the reverb tank connected (while bench testing, ect). The only thing that makes sense to me is maybe I've damaged the reverb tranny??
I'm at my wits end! Tried different tubes, voltages are all good, disconnected the vibrato circuit from the driver circuit and gone over the circuit many times.
I guess the next thing I could try is to bypass both the reverb and vibrato circuits to isolate the tone stack.
If anyone has any Ideas please help. I'm leaning to try a reverb trans.
Thanks and here's a few pics of it.


