John Greenland
CVRS Member

Perhaps another way to check the transformer is by measuring the heater circuit voltage. All the tubes except the 80 are connected to a 2.5 volt tap on the transformer.
With all the tubes in, the current draw on this winding is a bit above 12 amps.
What voltage do you need from the A.C. line to get 2.5 volts on the heater circuit with the tubes in their sockets.

I would think, that if that line voltage seems too low compared to normal line voltage then quite likely you have a transformer primary problem. thus messing up the turns ratio.

John G.