11-12-2011, 06:40 PM
codefox1 Wrote: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.Originaly the hum started within 30 sec. of power but disipated after about 5 min. when the volume and reception faded. now I have found that the 50a5 was breaking down so I replaced it and the radio opperated ok but now my voltages across the filters are about 10 volts more than they should be. Could this be due to the larger uf caps? if so, would I be able to drop the voltages to proper with a larger resistor between 1st and 2nd filter, which is now 220 ohm? how much of a voltage raise compared to the schematic would be acceptable?
