11-12-2011, 01:24 PM
If you did a total recap, and your DC voltages do not change when the hum begins, I think you may have a heater to cathode short in the 50A5. There should be 5 VDC on the cathode (pin7) relative to B-. To test this, hook a meter to read AC volts from the cathode to B-. Then let the radio play until the hum occurs. If you find AC on the cathode the tube is no good and must be replaced. If not, you will have to work backwards through the set to find the origin.
