My first thought is power supply capacitors.
Is the problem with the preamp or power amp? Test this by using the preamp out and power amp in jacks. Taking the preamp out into another power amp, does it work properly?
Well, I hooked it up again today on channel B, and there was immediately a loud, feedback-like hum at around a 9.5 volume level. This was 0 for the volume, and all other settings roughly at 2. I powered off the amp and ran a 3' cable from the master send to the return of a tested and working amp.
I plugged each amp in after verifying that there was no response from the Beta when attempting to power it on while disconnected from the mains, during which, the slave amp was plugged in and powered on. Playability seemed much better (but still erratic in volume and bad distortion) on B for a short time (A was still terribly noisy, though without the feedback occurring). I started to slowly turn up the drive, with one hand doing a hammeron at the 21st fret and letting it ring to listen to the decay, edging the drive up before repeating, going about a half-grade at a time. When I reached 6, as soon as I struck string, the feedback began slowly and increasing in volume as the note decayed. It was a markedly different tone, my note being E, and the feedback being somewhere around an F#, closer to G.
I cut off the power amp, and the feedback continued at a lesser volume, until I killed the Beta. I let them sit for a few minutes and powered the slave amp up, and verified that it was silent. I powered the Beta back up, and as soon as the power button had been engaged, the feedback was back at the same level it was before I cut power to either amp. It was as if I hadn't done anything at all when the sound had risen in the first place.
With a plug in the power amp in jack, does the power amp make noise? Running another preamp into it, does it operate properly?
If the problem is in the preamp, is the amp noisy with all controls at zero? If not, is it noisy with the controls turned up, but the input shorted?
The distortion/static noise is present at all dials at 0, just much lower intensity. At this point, I'm wondering if the preamp has a bad cap or two, and the master volume pot definitely needs replacing. I'm thinking caps because of that damnable feedback, and particularly the fact that it doesn't have a bell-curve to the intensity; it just keeps climbing and climbing. I also would've figured that tone would have dissipated, instead of still maintaining the same level prior to cutting power, though the amp
was still connected to the mains. . . hmm.
The master volume feels like it was probably torqued really hard by someone or something. When you turn the knob down to the point where it meets a normal feeling of resistance that occurs at the end of the range, the volume jumps from 0 to 10, as though the wiper jumped over and to the opposite end of the track. Edging it back up roughly 1/16th of a grade produces a loud static crack and then jumps down to 0. I was able to consistently reproduce that, at least.
I believe it is time to pull and recap the preamp section as soon as my components order comes in. Are there any particular pots that are recommended to use with these amps, or should I just go with Alpha? Also, any pointers of what I did that may have skewed my results would be great. I didn't follow all of the troubleshooting steps above, mostly due to the fact that the feedback was making it difficult to be able to turn the amp on consistently without fear of speakerdeath.
