09-27-2022, 06:56 AM
Hi RetroRev,
That wood case signal generator looks like it can generate FM signals, but the IF Output of it is likely 4.5MHz and the FM IF on your set is 9.1MHz (?). Most FM Sets are 10 MHz IF
I have not actually done it, but if you have another working radio, you can "tap" off signals from it to the radio under test. It is important that both radios have the same or very close IF frequencies. Most, but not all AM sets of the period have IF sections tuned to 455KHz. Per the N/A schematic, your set has a 460 KHz IF. However, the alignment instructions in the schematic state to set the signal generator to 455KHz. To be safe, both radios should be "transformer powered. If the "Tester Set" (The one being used as the "signal generator") is an AC-DC Set, use an isolation transformer or ensure that the chassis is at ground potential and not hot. Verify that the set under test does not have any leaky caps between the AC Line and chassis. In either case, ensure that that chassis is close to ground potential and connect the 2 chassis together. Connect a 100 pF capacitor to the plate of the IF Amp Tube of the "Tester Set". Connect the other end of that "cap" to a meter test lead (Shielding? Shielding? We don't need no stinking shielding!").
Prior to testing, verify that the Audio section of the set under test is still working, then get the stray cats out. In addition, test or replace the 6H6 Detector tube. This tube serves as both AM detector and FM Discriminator. In addition, "Ohm out" the IF and oscillator transformers and verify B+ at the plates of the IF, Mixer and Oscillator tubes.
Another test to perform is to tune the Tester set to a station in the middle of the broadcast band, use a wire wound around the oscillator tube of the set under test and loosely coupled to the antenna of the Tester Set, then tune the set under test across the AM Band. If while "sweeping" the dial of the set under test, howling or loss of signal occurs in the tester set, the local oscillator of the set under test is working. If not, the Oscillator is dead, and the cause of your issue.
Tune the Tester set to a station. Fully mesh the tuning cap of the set under test.
Now, with the chassis of the 2 radios connected and both radios powered up, attempt to inject the signal into the grid of the 2nd IF tube of the set under test. If signal, howling, etc. is heard, the 2nd IF stage is either good or partially good. If no joy, further troubleshoot that stage. Look for shorted caps (capacitors), especially any old paper caps or mica caps that you did not change. (Most folks don't change the mica caps, but they do go bad.). If a signal is heard, then work your way backward through the 1st IF and Mixer stages. In addition, follow the alignment steps in the schematic.
Hope this helps. Good luck!
That wood case signal generator looks like it can generate FM signals, but the IF Output of it is likely 4.5MHz and the FM IF on your set is 9.1MHz (?). Most FM Sets are 10 MHz IF
I have not actually done it, but if you have another working radio, you can "tap" off signals from it to the radio under test. It is important that both radios have the same or very close IF frequencies. Most, but not all AM sets of the period have IF sections tuned to 455KHz. Per the N/A schematic, your set has a 460 KHz IF. However, the alignment instructions in the schematic state to set the signal generator to 455KHz. To be safe, both radios should be "transformer powered. If the "Tester Set" (The one being used as the "signal generator") is an AC-DC Set, use an isolation transformer or ensure that the chassis is at ground potential and not hot. Verify that the set under test does not have any leaky caps between the AC Line and chassis. In either case, ensure that that chassis is close to ground potential and connect the 2 chassis together. Connect a 100 pF capacitor to the plate of the IF Amp Tube of the "Tester Set". Connect the other end of that "cap" to a meter test lead (Shielding? Shielding? We don't need no stinking shielding!").
Prior to testing, verify that the Audio section of the set under test is still working, then get the stray cats out. In addition, test or replace the 6H6 Detector tube. This tube serves as both AM detector and FM Discriminator. In addition, "Ohm out" the IF and oscillator transformers and verify B+ at the plates of the IF, Mixer and Oscillator tubes.
Another test to perform is to tune the Tester set to a station in the middle of the broadcast band, use a wire wound around the oscillator tube of the set under test and loosely coupled to the antenna of the Tester Set, then tune the set under test across the AM Band. If while "sweeping" the dial of the set under test, howling or loss of signal occurs in the tester set, the local oscillator of the set under test is working. If not, the Oscillator is dead, and the cause of your issue.
Tune the Tester set to a station. Fully mesh the tuning cap of the set under test.
Now, with the chassis of the 2 radios connected and both radios powered up, attempt to inject the signal into the grid of the 2nd IF tube of the set under test. If signal, howling, etc. is heard, the 2nd IF stage is either good or partially good. If no joy, further troubleshoot that stage. Look for shorted caps (capacitors), especially any old paper caps or mica caps that you did not change. (Most folks don't change the mica caps, but they do go bad.). If a signal is heard, then work your way backward through the 1st IF and Mixer stages. In addition, follow the alignment steps in the schematic.
Hope this helps. Good luck!
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
