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In Reply to: RE: Blown resistors posted by onthethreshold1 on April 04, 2015 at 20:08:41
Most Ampex 6973 amps don't use a traditional hum pot across the filament winding with wiper to ground. Many do use a pot to balance the current thru the finals. If the balance pot is misadjusted, hum will be present in the output.
Although your pic is incomplete, the fried resistors appear to be 100 ohm which corresponds to the cathode circuit of a typical Ampex 6973 output stage. These resistors could easily be damaged if a 6973 arced or shorted internally. Traditional hum pots and assoc. resistors connected across the filament winding rarely fail like they did in your pic.
Follow Ups:
Does the output stage look something like the schematic on the left? If so, then the problem prolly is shorted tube(s).
....and the pot is used to balance cathode current by effectively varying the g1 voltage inversely to each final of the PP pair. When current is balanced, the residual AC component riding on B+ is balanced out in the OPT...in theory. This is NOT the traditional hum balance pot in a filament circuit.
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