Thanks to all three of you for your responses. I have plugged the amp into a grounded wall socket with nothing else plugged into the outlet, and no preamp or other input to the amplifier, and the hum remains. It does sound about 60 hz or so, so I'm sure the "ground" hum verdict is correct. I have had the amp resting on brass cone points, as well as on its own stiff rubber feet, on my Target stand, and isolating it from ground vibrations doesn't seem to have any bearing on the problem. Neither does placing weights on top of it. The consensus opinion seems to be that repairs are called for. Any idea what such a repair might run, and/or where I should take/ship it? I hate to pay top dollar to a hi-end specialist if it's the kind of problem that a reasonably competent tv/audio shop repair guy could fix. I live in Charlotte, NC. Thanks, Ben
My "Hummer" is driving me nuts
I am new to tube equipment, so know very little about it. I purchased a British-made Grant power amplifier, 50 watts? per channel, four large tubes, four small ones. Sounds terrific, however, when the volume is turned all the way down, I can hear a low-frequency hum from both speakers. Not loud, but definitely discernable. Increasing volume does not affect the hum. I have ruled out the preamp as cause, having swapped in a second pre, also ruled out cable interference, as I've set up the system in two different rooms with different configurations and different cable and hum remains constant. My questions are, what might be the source of the hum? Will swapping out tubes eliminate it? Any suggestions on what steps to take next? Thanks! Ben