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I did find the RC coupled amp section in the RCA tube manual and have been experimenting. I currently have an 8.2K cathode resistor and 1M grid resistor. The hum/noise has definitely been reduced with no noticeable drop in gain.
Will try smaller values of cathode resistor and grid resistor.
Also experimented with a cathode bypass cap. Adding one to the circuit seems to increase the noise.
Tried shorting out the 0.002 input cap too. Not much difference either way.
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