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RE: help with Fisher KX-200

As Jim said, ignore the grid voltage - it's idle current you need to set. If you're using a low-cost DVM, it may read low with the 270K grid resistor in series - but should measure the voltage at the pots accurately.

Have you changed the caps in the negative supply? The first one carries about a half-amp of ripple current, and if it has a high ESR, heater voltage will be low. I've seen caps in a bias supply that measure nearly open without creating hum, due to the cancellation in the push-pull output stage.

Also, any leakage in the coupling caps will be a POSITIVE voltage, canceling some of the negative bias voltage. If you haven't changed them, do that first.


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