11-08-2020, 05:06 PM
Just thinking the 12AT7 heater pins 4&5 is what you would connect if feeding 12 volts. but your set is using 6 volt tubes except the rect tube. The 12AT7 heater is center tap to pin 9 to allow operation at 6 volts. You said something about dark tubes might be a easy fix check the connection to pins 4,5,9. Pins 4&5 should be tied together.
