The voltage scheme below.
Anyone know the problem?.
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tubes4hifi wrote:pin 7 is a grid, you can't expect to be able to measure grid voltages with most meters, as they will load the circuit down
that's the huge advantage of an old fashioned vacuum tube voltmeter, which has 11 megohm impedance or great.
Most modern DVMs only have around 1Mohm impedance.
If you are getting hum, most likely your source isn't grounded the same as the PAS preamp, or there is a poor ground connection somewhere, or more likely a ground loop.