1680 receiver hum

[John Q. Doe]

I recently acquired a HR-1680 receiver which appears to work with the
following exception.   If the AF gain is turned up all the way it is OK.
However, a hum appears when the gain is not all the way open.   I have no
schematic or manual, but suspect a capacitor problem.   Can anyone help with
a suggestion on how to fix this?

Bruce
Ocala, FL

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