Hi Myles -
I have two questions about my Vox AC-50 Classic Plus head.
1. I have noticed that the chassis vibrates when I turn the power switch on. It is not audible, but I can feel the vibration when I place my hand on the top of the head cabinet. Is this something to be concerned about?
2. Occasionally when I use the amp, I can hear a quiet but audible tone that sounds like an out of tune B-flat even with no guitar plugged in. Adjusting the volume controls on either channel has only a very slight impact on the tone. Swapping the phase inverter tube seemed to have mostly made the problem go away, but prior to doing that I noticed that I could get that tone to start and stop by lightly tapping one of the EL-34's or gently plucking the tube retainer springs. Would this B-flat tone be a result of microphonic power tubes, a problem with the filter caps, or was it the phase inverter?
The head is still under warranty as it was purchased new this year.
Thanks,
Mark
