Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bluebird on May 23, 2011, 05:08:03 pm

Title: Bassman Head Problem
Post by: bluebird on May 23, 2011, 05:08:03 pm

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.

Title: Re: Bassman Head Problem
Post by: blues man on May 25, 2011, 08:12:41 pm

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.

Title: Re: Bassman Head Problem
Post by: Jack1962 on May 26, 2011, 11:22:53 am

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 .

Title: Re: Bassman Head Problem
Post by: phsyconoodler on May 26, 2011, 12:00:46 pm

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

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