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Hi.. The remaining buzz could just be strong modulation from your source. The contrast control is basically a picture volume control and when turned up can overload the video amp (V5) which also amplifies the FM subcarrier.
However, it could be a weak V5 (6au6) too. An easy way to check this is to measure the voltage across the 6800ohm plate resistor(R138). It should be minimum 80V, normally around 100V.
Finally, assuming you checked the resistors around the ratio detector circuit,
imbalance in the 6AL5 double diode tube could be a cause.
BTW, for best overall performance the B+ buss should be close to 120V or half way between B++ and gnd. If needed I can give you a couple of ideas on how to correct.
Last edited by polyphase; 04-09-2011 at 12:00 AM.
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