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Amplifier Hum - Only Amp Connected

I have read many threads on here about various amplifier hum.

I recently bought a used tube amplifier.  When I connected the amp and turned it on, I immediately heard a hum from the mid-range driver of both speakers. The hum is audible even if the pre-amplifier is turned off/muted. In fact, I unplugged all interconnects from the amplifier and still heard a hum when the amp was on. I then unplugged the the interconnects and unplugged everything else in the room from the outlets (turntable, pre-amplifier, TV, and cable box), so that the only thing in the room connected to the wall was the amp. I still hear the hum from the speakers when it is only wall>power cord>amp>speaker cable>speaker.

This has to mean that it is a problem internal to the amp, correct?
jdpawnbroker
atmasphere's avatar
atmasphere
11,640 posts
 
I will try the cheater plug this evening. Does it make sense that a ground loop would be worse in one channel?
That hasn't been my experience but that does not mean it couldn't happen.
jdpawnbroker OP
10 posts
 
Cheater plug did not make a difference.  Hum was still there.

I swapped the power tubes and it is possible the worse side 
jea48
4,319 posts
 
jdpawnbroker OP6 posts

12-13-2019
5:33pm

Cheater plug did not make a difference. Hum was still there.

Did you put a piece of tape on the bottom of the cheater plug ground tab, or over the trim screw that hold on the electrical outlet cover plate, so the ground tab does not make electrical contact with the metal screw?
The trim screw is electrically connected to the equipment ground.
jdpawnbroker OP
10 posts
 
I did not use tape but the ground tab was not in contact with the screw.
atmasphere's avatar
atmasphere
11,640 posts
 
This sounds to me like a power supply problem such as a failing filter capacitor in the power supply. Such a part can indeed cause more hum in one channel than the other but the problem would be in both. Sometimes you might be able to get it to stop humming for a little bit by simply turning the amp off and on again, but only sometimes. My recommendation is to seek service on the amplifier.
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