Peavey Classic 30 Fillaments not working (sort of....)

[wizard333]

Peavey Classic 30, preamp tube filaments wont light. Found a broken jumper causing pin 4 of V1 not to see ground. Thought that was it. Well, that was undoubtedly part, but nope. Now here's the kicker: Tested the -36V supply, check. Tested voltage drop across pins 4 and 5 of each tube, getting 12v ish drop across each tube. Changed tubes. Same readings, but tubes still won't light and are not working. Plate voltages present.

Since the filament supply voltage is present and the expected drop across each is present, I'd expect they'd light up and work, but nope. Any ideas?

[Enzo]

Don't know. Check along the string, do you find 12, 24 volts to ground?

Plate voltage present? OK, at the plates is it full B+ or is there drop across the plate resistors? If the tubes are not working there should be zero volts on each cathode. Turn out the room lights, any chance the things are lit but hard to see?

[wizard333]

Well never mind, took them off the load and ran into a cab and once ground issue on pin 4 v1 is fixed they do seem to make sound, but still don't light up. Guess they just don't with that series heater thing going on?

[wizard333]

Don't know. Check along the string, do you find 12, 24 volts to ground?

Plate voltage present? OK, at the plates is it full B+ or is there drop across the plate resistors? If the tubes are not working there should be zero volts on each cathode. Turn out the room lights, any chance the things are lit but hard to see?

Yep checked all that and they do seem to make sound after the ground issue was fixed, but they just don't look lit at all, tried several tube brands just to see. Very odd.

[J M Fahey]

What do you measure across each tube pins 4 and 5?