[Boatanchors] 75A-2 NOISE PROBLEM

[Schichler, Donald]

I recently acquired a 75A-2 which seems to work OK except for one problem.  When I engage the crystal filter (use a selectivity position other than 0) there is a steady 60 Hz buzz that varies with the audio gain setting.  The noise limiter greatly reduces it, but I would like to be able to use the radio without it engaged.  I hear the noise in both AM and CW mode, but it sounds very clean with the selectivity switch in position 0.  Any ideas on where to look?  I'm thinking there might be a bad capacitor or tube somewhere.
 
Thanks and 73,
Don W2DAS