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Post subject: Blues Deluxe humming loudly
Posted: Mon Jan 19, 2009 11:25 pm
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Hi - I have a US-made Blues Deluxe tweed which I bought used. It has a loud, steady hum when I take it off Standby. None of the controls seem to impact the humming. I have other tube amps in the same room, same circuit, no problems with them. Switching guitars doesn't matter. It is plugged into a good power filter/conditioner. If there is no guitar cable plugged in when I take it off Standby, the humming is *really* loud - like full volume loud - and it makes other very loud noises. It doesn't seem to matter much which input I use, the hum is still there. I also use a good noise suppressor connected before the amp and in the FX loop, which removes the gain noise from the amp itself. So I guess the hum comes in after the FX loop. Adjusting the noise suppressor has no impact on the hum, but does remove the amp gain noise. Removing my pedals doesn't seem to matter. The amp is silent until I take it off standby. I tried swapping power tubes, but I only had old ones of very questionable quality. It didn't seem to make any difference with two other sets of the old power tubes. I noticed that the power tubes that were in it are different brands, which is odd. One has more of a blue glow to it, but they generally look OK. That's about all I can think to tell you to start with.

So if I buy new power tubes, could I expect better results? Or is there likely something else wrong with this amp? Anything else I can check to try to save myself a trip to the repair shop? Other than the humming, it sounds awesome.

Thanks for any pointers!


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Post subject: problem solved, I guess
Posted: Tue Jan 20, 2009 1:44 am
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I think I've solved my hum problem. Just 'cause, I decided to plug the amp in on a different circuit in my house. When I did - no hum, no screeching, almost total silence. So I brought it back and plugged back in where it was plugged in before - no hum. Then I realized that to move the amp, I had unhooked my rack noise suppression, which is connected to the FX loop. I connected it up again and the hum was back. The noise suppressor has 3 ground lift switches on the back of it. I tried several combinations, and one combination took away the hum. I had set those switches long ago, but I think a recent equipment move in that rack may have caused a cable to bump into those switches. It takes very little pressure to turn those switches on/off. So it looks like some sort of grounding problem that I don't understand, but which seems to be resolved.


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