07-18-2024, 08:36 PM
Hi Dave,
I had COVID too
Try this:
Power off and disconnect the screw terminals. Unplug the speaker field coil.
Measure the total resistance of the R11 "voltage divider" resistor between Terminal 5 and chassis ground. Measure between Terminal 4 and ground. That resistance should be a little less than half the resistance between Terminal 5 and ground. Note these values. Note the DC resistance of the field coil. I believe that it should be similar to the value received from measuring between terminal 5 and chassis ground. My rational for this is that the Plate voltage for the output tubes is 250V. One end of the field coil connects to the point that supplies the output transformer. The plate voltage for the RF amps is supposed to be 120V. This comes from the other end of the field coil which is essentially part of the voltage divider. (Terminal 5.) The screen voltages of 70V come from Terminal 4.
Reconnect all after troubleshooting.
Measure voltage at terminal 5. It should be 150V. If it is much more than that, the speaker field coil met have shorted turns or be the wrong one.
Measure voltage at terminal 4. It should be 70V, and about half of the terminal 5 voltage. If both voltages are high but proportional, then
the speaker field may be at issue. If the terminal 4 voltage is low, then something is loading it down. Check C13, 14 and 15 for shorts.
Unfortunately, the diagram does not give resistance values for the speaker field or for the voltage divider.
If you touch the antenna to the grid cap of the 2nd RF tube, you should receive a very loud signal, considering that your volume control is trashed.
I don't know of the volume control is wirewound or not. However, you can do one of 2 things.
There were 2 different volume controls used for this set. One control had both the antenna and cathode bias pots being 10K. the other control had (I believe) an antenna pot of 50KOhm and the cathode bias pot being 5KOhm. I believe that these are linear taper, as opposed to audio tape, used in modern amps and receivers.
The voltage divider that includes the cathode bias pot has a total resistance of 31,500Ohm if the 5K pot is used. At 70V, current through this total resistance of 31,500Ohm is only 0.0222 Amp. Power dissipation through the entire resistor network is only 0.15W, so a 0.5W 5K or 10K pot will work just fine for the cathode bias portion of the circuit. The antenna portion should likely be 50KOhm. If possible, get 2 pots. Otherwise, if you can get a ganged 10K 0.5W linear taper pot, this will do just fine.
Hope this helps!
I had COVID too
Try this:
Power off and disconnect the screw terminals. Unplug the speaker field coil.
Measure the total resistance of the R11 "voltage divider" resistor between Terminal 5 and chassis ground. Measure between Terminal 4 and ground. That resistance should be a little less than half the resistance between Terminal 5 and ground. Note these values. Note the DC resistance of the field coil. I believe that it should be similar to the value received from measuring between terminal 5 and chassis ground. My rational for this is that the Plate voltage for the output tubes is 250V. One end of the field coil connects to the point that supplies the output transformer. The plate voltage for the RF amps is supposed to be 120V. This comes from the other end of the field coil which is essentially part of the voltage divider. (Terminal 5.) The screen voltages of 70V come from Terminal 4.
Reconnect all after troubleshooting.
Measure voltage at terminal 5. It should be 150V. If it is much more than that, the speaker field coil met have shorted turns or be the wrong one.
Measure voltage at terminal 4. It should be 70V, and about half of the terminal 5 voltage. If both voltages are high but proportional, then
the speaker field may be at issue. If the terminal 4 voltage is low, then something is loading it down. Check C13, 14 and 15 for shorts.
Unfortunately, the diagram does not give resistance values for the speaker field or for the voltage divider.
If you touch the antenna to the grid cap of the 2nd RF tube, you should receive a very loud signal, considering that your volume control is trashed.
I don't know of the volume control is wirewound or not. However, you can do one of 2 things.
There were 2 different volume controls used for this set. One control had both the antenna and cathode bias pots being 10K. the other control had (I believe) an antenna pot of 50KOhm and the cathode bias pot being 5KOhm. I believe that these are linear taper, as opposed to audio tape, used in modern amps and receivers.
The voltage divider that includes the cathode bias pot has a total resistance of 31,500Ohm if the 5K pot is used. At 70V, current through this total resistance of 31,500Ohm is only 0.0222 Amp. Power dissipation through the entire resistor network is only 0.15W, so a 0.5W 5K or 10K pot will work just fine for the cathode bias portion of the circuit. The antenna portion should likely be 50KOhm. If possible, get 2 pots. Otherwise, if you can get a ganged 10K 0.5W linear taper pot, this will do just fine.
Hope this helps!
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
