77 Marshall JMP 50 watt lead II issues

[billd76]

The amp will not play any sound at all unless the master is turned up to 5, and is very loud on 5. only sound I get is when I pluck a string. It almost sounds like bad or dirty pots. I pulled the chassis this morning and sprayed the pots with Peavy "Get the Funk out". I don't think its the issue but simple to do and worth a shot and certainly can't hurt. May ship it to the guy in California that works on Marshalls if this doesn't work. I'll send some pics later this morning of the guts! Thanks all. Bias Issue? all new tubes 6550s for power. Transformer good. everything checks out but getting crossover distortion on the scope wave. scope image attached. Thanks

[pdf64]

What plate or cathode current are the power tubes pulling at idle?

[m1989jmp]

The amp will not play any sound at all unless the master is turned up to 5, and is very loud on 5. only sound I get is when I pluck a string. It almost sounds like bad or dirty pots. I pulled the chassis this morning and sprayed the pots with Peavy "Get the Funk out". I don't think its the issue but simple to do and worth a shot and certainly can't hurt. May ship it to the guy in California that works on Marshalls if this doesn't work. I'll send some pics later this morning of the guts! Thanks all. Bias Issue? all new tubes 6550s for power. Transformer good. everything checks out but getting crossover distortion on the scope wave. scope image attached. Thanks

Certainly a bias issue, but it shouldn't affect amp's volume that drastically. Is the bias trimpot maxed out (turned all the way)? If so, someone will need to change the bias range resistor, because you can't get it hot enough.

Maybe the volume pot is bad too, is it original to the amp?