Problem with a plexi

[JC@]

I have a problem with a reissue 50 watt plexi.
It blew the mains fuse, and a screen resistor, by the way. Now it has the resistor replaced and new tubes, but it distorsts from the begining of the vol pots on both channels. May it be the output transformer?
Thanks for your help.

[melvin]

I wouldn't jump to that conclusion. You need more info. I would check the voltages and bias current through the output tubes. Do you have a schematic?

[JC@]

Except for the effects loop I believe it is the same schem as the original. I will check all voltages in the output tubes, but I woul say that the bias circuit is correct or at least working as I biased them at 32mA each...
What makes me think about the transformer is that I was told that the amp was working correctly until the screen resistor blew, and I can't think in anything else that may have gone bad along with that resistor.

[JC@]

The clipping/bad signal begins in the phase inverter, but the tube is good.

[acorkos]

make sure your effects loop jacks are clean

[JC@]

make sure your effects loop jacks are clean

I jumpered the send and return jacks but the problem persists...

[acorkos]

meter both power tube screen resistors. measure the voltages on pins 3/4/5 of the power tubes and pins 1/3/6/8 of the 12AX7's. you gotta rule out the simple/cheap stuff before dropping the dough for a new output transformer.