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Just got a Hickok 539b recently. Seems to work ok but the grid bias meter didn't work. Took it apart and found that metal contacts from the moving coil to the meter body oxidized enough to open up. After cleaning contacts it started to work. Upon trying to calibrate the bias circuit, the voltage to the tube socket has sufficient potential on both 10 and 50 volt ranges but the meter barely moves up scale. There are 200 ohm shunt and 9900 ohm external multiplier resistors in the circuit. I measured both and they are accurate. By putting a pot in place of the shunt I can get the meter to deflect and calibrate correctly. But I shouldn't have to. I did see an internal multiplier resistor inside the meter which I think has changed value. Should I dive back inside the meter and test that resistor or just leave it alone? Any idea what the full scale range is with the multiplier in place?

Also is there a parts layout for all the pots? I've identified most but there are three I haven't traced out and identified.

Thanks for looking.

You best bet would to buy a pannel mount digital meter , for the bias meter , the oringinal one is hard to read . Its the same as on the 539C i use and find it hard o use . Most people mount the digital meter in the wooden case pocket .
http://www.stevenjohnson.com/hickok/data.htm