43 Volts to the speaker?

[JMC]

I have a Sunn Betabass that is giving me some trouble.  When it is powered on, the speaker starts to hum loudly.  I've tested on different cabinets with the same result, so it's not the speaker.

I recruited a friend who is an electronics technician to help me troubleshoot the system.  We found 43 volts at the speaker outputs (?!?!?!).  We assumed a short somewhere so we checked all the resistors, capacitors, diodes, transistors, transformer and rectifier.  Everything seems fine.  One transistor (Q1 I believe) was VERY hot after being powered on for a few minutes (with the speaker disconnected of course), but it seems to test fine.

Does anyone have any suggestions on what to check or replace?

Thanks,
Jeff
ten_core@hotmail.com

[Don T.]

Hello;
 OK, first thing. It's not possible for everything to check out fine and the amp to have such an obvious problem. It is not black magic. That being said, Is it DC or AC at the outputs? In other words do you have hum riding on a DC voltage or is it outputting 43 volts of AC at say 60hz? 43v is right at the DC rail of the amp. Remember you can not check power supply caps with out them being at full voltage. They will check fine using a capacitance meter but may fail at rated voltage and warm. Could be your rectifier is bad. Could be a transistor or predrive shorted. Well, the list could go on and on because more diagnostic info is needed.
Don T.