Quote:
Originally Posted by 6x47
"38-40ma measured at the plates"!
Just curious, how do YOU measure current at the plates?
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Well, I don't know how Dacious does it, but I do it like this:
For fixed bias amps, I measure the total current with a bias adapter, which is just a tube socket fitted on a tube base, with a 1 ohm, 1% resistor in the cathode path, and test leads hanging out the side. I=V/R, since R=1, # amps = #volts.
But then you have to deduct the screen current, so measure voltage drop over the screen resistor, use ohms law; done. You have to actually measure the value of the screen resistor, not just use the nominal value.
For cathode bias it's just the same, except I don't use the adapter, just measure straight over the cathode R.
Some amps have a 1ohm resistor built in, so you just measure over that instead.
That's all there is to it.
To calculate plate dissipation, you have to measure a few more things.
steven