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Amp transformer buzz/hum from DC on AC line?

I have two tube monoblocks with EI type transformers.
One amp hums much more than the other. Not through speakers. It gets somewhat louder and much warmer than its counterpart over time(3-4 hours).
They are on different circuits, I have tried swapping circuits. I have isolated it by turning off every breaker except the one to the amp, so it's not from somewhere else in the house. I have swapped all the output tubes from one to the other.
I have measured .46 volts DC on the line to both amps. Could the one be more sensitive to DC than the other?
Is this enough DC to cause a problem? I can get a PS audio Humbuster on free trial to make sure, but it sounds too good to be true. Any thoughts?
mrmatt

Showing 1 response by jea48

jea48
4,303 posts
 
I have measured .46 volts DC on the line to both amps.
How did you go about measuring the DC voltage on the AC line.

DC voltage on the line can cause transformer mechanical noise.

http://sound.westhost.com/xfmr.htm#7-noise

http://www.diyaudio.com/forums/solid-state/2080-dc-filter.html

http://www.altavistaaudio.com/hum.html#trafo
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