No sound - volume knobs are ineffective

[Enzo]

The PV Classic 30 wires the heaters in series. The four power tubes are in series across the AC of the power transformer winding. The three 12AX7 preamp tubes are in series across the -36VDC supply. No diode in either place.

perhaps you recall a shorted flyback diode from output plate to ground. Those will pop the B+ fuse instantly.

[mykey]

The PV Classic 30 wires the heaters in series. The four power tubes are in series across the AC of the power transformer winding. The three 12AX7 preamp tubes are in series across the -36VDC supply. No diode in either place.

perhaps you recall a shorted flyback diode from output plate to ground. Those will pop the B+ fuse instantly.

perhaps this classic model does not have the diode in the heater circuit to reduce the heater hum, but i have seen several that do.
the first person to point this out to me was a technician at the PV factory. I managed a PV authorized service center for several years. not entirely sure that this diode appears on the schematics, but it's something to keep in mind seeing that it is one unusual design feature of PV amplifiers.

[Enzo]

PV schematics are as a rule very complete and accurate. Unlikely to find parts on the amp not on the drawing. There are no diodes to ground from the heater lines on any of the amps called Classic (Classic, Classic VT, Classic VTX), nor on the C30, or the CLassic 50. I didn't chack the stereo power amps or the larger less popular ones. The Classic 20 has a couple diodes to ground from the heater winding, but they are joined by two more on the hot side, since they make up a bridge to rectify the heater AC for the preamp tubes running on DC.

SInce the original poster has a C30, I think it prudent that we discuss the circuits that are actually in that amp. I generally refer to the schematics of the amp in question in these forums, you might consider doing the same. Telling him about something on another model that doesn't exist on his is not going to help him and would only serve to confuse him.