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Post by benttop (Steve) on Feb 12, 2009 18:53:58 GMT -7
One thing - don't unplug your speakers while the amp is on! That can cause a real electronic problem in your output transformer, so that would be a bad diagnostic technique.
Is the hum affected by any of the controls on the amp?
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Post by benttop (Steve) on Feb 12, 2009 23:37:40 GMT -7
Mismatched power tubes can cause this. And just about any preamp tube could cause it. Since your controls don't affect it, that limits the source to the PI or power tubes. Have you changed the Phase Inverter tube?
Oh I suppose there is a very small chance that something about the rectifier could cause this, but it is a pretty small chance. Nevertheless, have you tried replacing it?
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Post by rhythmeister on Feb 13, 2009 1:47:42 GMT -7
As anyone here will attest, I'm no amp tech. BUT, I've been able to get rid of humming/buzzing noises in all of my tube heads by tightening the chassis bolts (the big ones on the bottom of the head). Get those good and snug and then try. I can't explain how they get loose (not from me loosening them), but this has worked for me on 4 different heads I own.
Cheers, Blair
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