My 5F1 Champ is Sick - Low sound output and glowing 6v6 tube

[Randall]

Agree with MJWB, I see no ground reference in your heater circuit. If your transformer does not have a center tap for the filaments, and you want to take the green wires directly to the lamp and heaters, you are going to want to run a pair of 100 ohm 1/2 watt resistors from either side to ground. At the lamp is a good place to do this. 44 volts on your heaters is not right, it should be 3.3vac to ground.

Also, I believe you have the black and yellow wires reversed on your speaker jack. I'd pull that yellow wire slack into the chassis as well. I see some solder iron melt marks on some of your wire, I'd probe around with a chopstick to see if something might be shorting out there.

[g1]

This amp was playing fine and then one day it just sort of cut out and now has low output.

This is important as this thread is old and was dealing with other problems. Also note he has checked the speaker and tried other tubes.
A bad connection or faulty component would be likely suspects. I don't believe it is a build issue as it was working fine previously.
MWJB was suspicious of the OT and suggested checking the turns ratio. That would be a good check to make.

[MWJB]

Heaters are dc referenced at the 6V6 tube socket, pins 2 & 7 have 100ohm resistors to pin 8.

44 volts, whether AC or dc is not right for the heaters. You should, as Randall says, have ~3.3VAC from each leg to ground and 6V6 cathode voltage in dc floating on top of that. You quote 20v for the 6V6 cathode...so I'm not sure where this extra 24VAC is coming from.

Temporarily eliminate the dc reference & ground the 100ohm resistors to the chassis. Then you should just have 3.3VAC from each leg to ground, no dc.

@G-one "I don't believe it is a build issue as it was working fine previously."...ha, ha, if it wasn't a build issue it would still be working flawlessly in 20yrs! ;-)

Wittgenstein, turn the amp off & unplug from the wall, what is the ohms reading from B+ wire to 6V6 pin 3, should be ~270ohms for a champ OT (rough test, until you confirm turns ratio).

By the way, you left off the 25uf/25v cap from the 12AX7 cathode at pin 3 ;-)