03-20-2013, 05:20 PM
Still maybe one or more microphonic tubes or
Possibly the tuning gang rubber mounts are petrified and causing the capacitance of the tuning gang to change in response to the vibrations. At loud audio levels this can also cause a feedback "howl" sometimes due to speaker vibrations. Your tapping does the same thing. Try lightly tapping the tuning gang to see if it's the cause.
Just two things to try.
Chcuk
Possibly the tuning gang rubber mounts are petrified and causing the capacitance of the tuning gang to change in response to the vibrations. At loud audio levels this can also cause a feedback "howl" sometimes due to speaker vibrations. Your tapping does the same thing. Try lightly tapping the tuning gang to see if it's the cause.
Just two things to try.
Chcuk
Chuck Schwark,
The Philco Repair Bench
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