I have a peavy studio pro 112 transtube red stripe model. when the tdynamics control is turned to 50% it has a weird and loud oscillating hum there is also dc voltage at speaker wires. the voltage varies between 5 and 8 volts on my dmm. i was wanting some suggestions on where to start troubleshooting i would like to fix the amp myself. i got the amp cheap and thought it would be a great way to learn.