Bassman AB165 to AA864 Normal Channel Issue

[ebulakowski]

Hello everyone,

I have a Silverface Bassman on the bench that was modded by a previous "tech" beyond all recognition. None of the parts values matched the schematic, parts were tack soldered to other parts that were floating above the eyelet board, a total mess.

I have since ripped all of the guts out and am in the process of wiring it to the AA864 spec using the Mojotone Layout attached below.
I am now in the testing process and am encountering an issue with the Normal Channel Volume and EQ. Turning the Volume pot is very crackly and the volume increases, but even when maxed out it reaches a volume comparable to a "5" on a similar amp. The Treble and Bass controls are also very crackly and seem to work until about halfway on the pot, and then the signal cuts out entirely. I've replaced the pots, the 12ax7 that is responsible for that channel, and completely rebuilt that channel with new parts as a final act of desperation...and am still running into the same problem. I've scrutinized the layout and the AA864 schematic and everything appears to be correct. I'm getting ground continuity to chassis at all the specified places, and the test point voltages I've measured are within range of those on the schematic. My guess is I'm getting a AC current leak to those pots somewhere, but can't figure out where or how.

[vampwizzard]

Check your voltages, double check solder joints. Make sure youre not accidentally grounding something that shouldnt be grounded.

[sluckey]

Did you replace the fiber board?

[ebulakowski]

Did you replace the fiber board?

I did not replace the fiberboard. If the problem was also present in the Bass Channel, (which it isn't and it sounds great), I'd maybe think it was conductance through the fiberboard, unless my thinking on that is incorrect.