02-25-2022, 04:07 PM
Ralph, If you are hearing the IF signal when you connect your signal generator to the cap of the 78 tube but not when connected to the cap of the 6A7, there must be a problem between those stages. You should hear a loud 460 kc IF signal when connected to the 6A7 grid cap.
I would first check the IF transformer between the 6A7 plate and 78 grid for continuity. Both the primary and secondary windings should read less than 100 ohms. If the primary is open, you will have no plate voltage on the 6A7 and therefore hear no signal. Check the voltages on the 6A7 tube pins and compare to the typical readings given in the service info.
Don't worry about replacing mica caps until you have checked the other possibilities. Micas are pretty reliable and rarely need replacement.
I would first check the IF transformer between the 6A7 plate and 78 grid for continuity. Both the primary and secondary windings should read less than 100 ohms. If the primary is open, you will have no plate voltage on the 6A7 and therefore hear no signal. Check the voltages on the 6A7 tube pins and compare to the typical readings given in the service info.
Don't worry about replacing mica caps until you have checked the other possibilities. Micas are pretty reliable and rarely need replacement.
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