01-20-2023, 05:55 AM
Hi Mr. Big,
One thing I missed your answer to. Is there static as you turn the tuner, and the static stops after you turn the tuner? (Kinda like a scratchy volume control?)
I had a similar set that drove me crazy until I cleaned the cap by using a, air gun and feeler gauge between the meshed plates of the variable cap. I could not see the crystallized aluminum fragments, but they must have been there. I am suspecting that if the problem is the variable tuning cap, then the issue is in the "RF" section and not the oscillator section.
You can try signal injection. Is the static loud? Does it vary with the position of the volume control? If so, and the volume control is not the cause of the static, then the AF section is good. Confirm by injecting an audio signal.
There are 2 "classic" methods of troubleshooting, signal injection and signal tracing. Signal injection involves a signal generator that is tunable across both the broadcast band and the IF Frequency. This device is usually modulated by a 400 Hz oscillator or externally modulated. You inject the signal, usually at IF frequency, starting at the detector. If the tone from the generator is heard, then inject at the grid of the IF Amp tube. if the tone is heard, then inject at the plate of the Convertor. If heard, then inject at the grid. Then inject RF at the grid. If you have access to a signal generator, this is your best bet, as this tool is also used to align the radio.
In signal tracing, the tracing rig or probe must have a detector in circuit and an audio amp after the detector. One starts at the front end of the radio and attempts to detect a signal. If the signal tracer is sensitive, tunable and there is a very strong station, start at the antenna, then the grid circuit of the convertor (in your radio at C5). Then go to the IF Frequency and check at the plate circuit of the convertor. If a signal is detected, then go to the grid of the IF until the signal is lost.
Another trick:
Do you have an all wave receiver that has a "long wave" (about 100 - 500 KHz) band? If so, tune around 455 KHz to pick up the IF and place near the radio, then attempt to tune the radio in question.
Is there a lot of static and noise at the upper end of the dial?
One other possibility. This radio may be "transitional" between pre-war and post-war. Pre-war IF transformers were tuned by "trimmer" caps. Post-war radios were tuned by slugs. The transformers had mica caps across the coil. These caps suffer from what radio enthusiasts call "silver mica disease" where the cap intermittently shorts out. However, when this happens, the noise is across the board.
A pic of the top side and underside or the radio would help.
Good luck
One thing I missed your answer to. Is there static as you turn the tuner, and the static stops after you turn the tuner? (Kinda like a scratchy volume control?)
I had a similar set that drove me crazy until I cleaned the cap by using a, air gun and feeler gauge between the meshed plates of the variable cap. I could not see the crystallized aluminum fragments, but they must have been there. I am suspecting that if the problem is the variable tuning cap, then the issue is in the "RF" section and not the oscillator section.
You can try signal injection. Is the static loud? Does it vary with the position of the volume control? If so, and the volume control is not the cause of the static, then the AF section is good. Confirm by injecting an audio signal.
There are 2 "classic" methods of troubleshooting, signal injection and signal tracing. Signal injection involves a signal generator that is tunable across both the broadcast band and the IF Frequency. This device is usually modulated by a 400 Hz oscillator or externally modulated. You inject the signal, usually at IF frequency, starting at the detector. If the tone from the generator is heard, then inject at the grid of the IF Amp tube. if the tone is heard, then inject at the plate of the Convertor. If heard, then inject at the grid. Then inject RF at the grid. If you have access to a signal generator, this is your best bet, as this tool is also used to align the radio.
In signal tracing, the tracing rig or probe must have a detector in circuit and an audio amp after the detector. One starts at the front end of the radio and attempts to detect a signal. If the signal tracer is sensitive, tunable and there is a very strong station, start at the antenna, then the grid circuit of the convertor (in your radio at C5). Then go to the IF Frequency and check at the plate circuit of the convertor. If a signal is detected, then go to the grid of the IF until the signal is lost.
Another trick:
Do you have an all wave receiver that has a "long wave" (about 100 - 500 KHz) band? If so, tune around 455 KHz to pick up the IF and place near the radio, then attempt to tune the radio in question.
Is there a lot of static and noise at the upper end of the dial?
One other possibility. This radio may be "transitional" between pre-war and post-war. Pre-war IF transformers were tuned by "trimmer" caps. Post-war radios were tuned by slugs. The transformers had mica caps across the coil. These caps suffer from what radio enthusiasts call "silver mica disease" where the cap intermittently shorts out. However, when this happens, the noise is across the board.
A pic of the top side and underside or the radio would help.
Good luck
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
