ground loop hum

[bgf]

aggravating ground loop hum from one of the monoblocks. it increases and decreases with time. worse when other stereo electronics are on.  I thought it was a space heater, overhead lights, outside hvac.   some times I turn on system and it is absent entirely. I have played with cleaning points on tubes, resoldering power points on that mono block. tested outlets to see if they are wired incorrectly.  running out of ideas.  any thoughts would be much appreciated.  thanks

[Doc B.]

Swap tubes with the other amp, see if it follows.

Are both amps on the same circuit? If not, try to get all of your gear on the same circuit.

Reflow every ground connection in the amp.

Check for proper installation of the power transformer mounting washers and tightness of the mounting screws.

[Paul Birkeland]

Tell us more about the system.  What's in the system?  Is everything plugged into the same outlet?  Have you measured the available AC voltage with nothing turned on, then everything turned on? 

If it's a ground loop hum, it should completely go away when you unplug the signal cable going to that amp.

-PB

[bgf]

thanks for the input will try those suggestion and get back to you.