Choke question

[loudthud]

The pin 8 voltage only jumping to 75mV is consistant with playing at a low level, guessing <10W off the top of my head. The OT is probably ok, an internal or external short would likely cause larger currents in the power tubes. About the only thing left is some kind of short or low impedance in the signal path. Perhaps a 1K pot where a 1 Meg should be, a wrong resisitor somewhere, a wire missing or touching the chassis, some kind of build error. You haven't posted any schematic or gut shots so I can only guess.

If you used eyelet/turret board construction with wires on the back side of the board, use your ohm meter to verify all those wires from the top side. They may not be connected where you think they are. Hunt around with the ohm meter looking for a low resistance where there shouldn't be one.

[Bob D]

Earlier when I checked the sound with the negative feedback disconnected I noted that it got louder, concluded that it was in fact negative feedback and moved on. What I did not notice was how much louder it got. Without the negative feedback connected it performs like a ~50 watt amp should.

I measured the voltage across the speaker terminals and I got about 3.5 millivolts AC. Sounds about right.

Looking at my layout I notice that I twisted the wires that connect the PI plate resistors to the PI socket (something I don't normally do). Could this cause my problem?

[loudthud]

If you reverse the wires from the PI plates, the power amp should oscillate. Sometimes you will hear it, sometimes it's ultrasonic, you can't hear it but it should show up in the VAC measurement. If the problem is too much feedback, look for a wrong resistor in the feedback network or a bad Presence pot or cap.