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Had this unit for repair and there was a crackling sound with the master volume control turned up....the higher it was the louder the noise.....turn it all the way down and it disappeared.....put a scope on the volume control and the noise was visable....the noise was on the plates of the phase inverter......was not a tube problem....turns out there was a resistor which supplies plate voltage to one side of the inverter and was more than double in value...replaced it and problem solved.....
Had to use two resistors to get the value I needed.....the final reading was off by a couple K ohms......so I pulled the other plate load resistor and did the same thing just to keep everything balanced.....worked like a charm.....the resistor in question was R66....Hope this helps somebody out in the future.....
Cheers
Had to use two resistors to get the value I needed.....the final reading was off by a couple K ohms......so I pulled the other plate load resistor and did the same thing just to keep everything balanced.....worked like a charm.....the resistor in question was R66....Hope this helps somebody out in the future.....
Cheers