Red Glowing tubes, Fender Twin Reverb

[billwjr]

Looking at a Fender Twin Reverb AA769, I've got no bias voltage. The bias supply feeds the vibrato section, which is now disconnected from the bias circuit. I've disconnected the coupling caps from the driver stage. I've disconnected the power transformer leads, and the B+ and bias tap are OK, 332 and 55 VAC. Nothing is shorted to the chassis. I have replaced all the filter caps. Any thoughts appreciated.

[Alex R]

Check the reverse diode that feeds tyhe bias supply. It's on the little board by the pilot light, next to the bank of six diodes that feed the HT. It has a resistor running to it - should be some AC volts that side, and DC the other side.

[Bruce / Mission Amps]

Looking at a Fender Twin Reverb AA769, I've got no bias voltage. The bias supply feeds the vibrato section, which is now disconnected from the bias circuit. I've disconnected the coupling caps from the driver stage. I've disconnected the power transformer leads, and the B+ and bias tap are OK, 332 and 55 VAC. Nothing is shorted to the chassis. I have replaced all the filter caps. Any thoughts appreciated.

Is there any -DC voltage at the bias filter cap?