Bassman Head Problem

[bluebird]

Hello from france Everbody!
I'm restoring a bassman head (blonde circuit but with a diode rectifier not a gz34)

i replaced all the electrolytics, power filter caps, power supply resistors, bias cap....cleaning all pots, switches... and  sometimes when i switch the stand by the amp has only 160-165v on the phase inverter 100k resistors instead of 300-305v. When it warms up the voltage becomes ok again and the sound is ok again too...it's a mystery, if someone got a idea it would be cool!!
many thanks
hervé

more info : i have 445-450v out of the diode rectifier, negative feedback is ok at -56v.

[blues man]

I would check your solder joints and that part of the power supply that feeds the phase inverter. If you didn't replace all the caps I would definitely be checking them. you could have a bad resistor that changes values after the amp heats up. Did you check the resistor values when you pulled the caps to replace them. This is a good time to do so. Change the phase inverter tube and see what happens. These are just ideas.

[Jack1962]

how long of a time period is it between turning on the amp that you are getting this 160 to 165v on the PI, the tubes do have to warm up .

[phsyconoodler]

Quote:"negative feedback is ok at -56v."

You must mean BIAS voltage.  Indeed recheck you filter cap solder joints,especially the ground side.