fender amp problem

[JC@]

hi
I'm having a problem with a fender clone, but a twin reverb schem is ok to illustrate it.
I get ugly distortion, and I tracked it to pin 2 for a grid of the PI tube. The signal shows distorted and flattened on the lower side of the wave.
I get correct dc on both plates but with .5 AC on them
Feedback lifted and the problems persists
Well, help me please

[Lee_ranaldo]

mmm

check every resistor value from the PI with a multimeter
change the electrolitic cathode bypass caps.

check that there is no soldering touching the chassis underneath the board.

i will replace those 0,1 uf poly-film or (chocolate drop) caps (that goes from the PI tube to the output tubes) because they might have DC leakage on them

But go simple first like changing pre-amp tubes, checking voltages according to the schematic.

u might have ultrasonic parasitic oscilation on the pre-amp , that cuts lots of headroom in the output stage making it to sound like a "broken speaker" without having a broken speaker

[melvin]

one side of the wave being 'flattened' does not seem terribly unusual. Does the output of the previous stage have the same form?

did you mean .5V on the plates of the PI with no signal input? If so, what does that look like?

And what does the amp sound like?