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In Reply to: RE: Yeah, check the plate voltages when the bias reads differently posted by Michael Samra on May 14, 2014 at 15:17:07
Thanks Mike! Will add that to my list of things to try.
"I know just enough to get into trouble. But not enough to get out of it."
Follow Ups:
Maybe able to find a pattern.
Somethings been nagging at me. When I used to check my output bias and DC balance every 6 months or so, I thought I always had to change from DC mA to DC volt settings along with switching one of the test leads. But at some point I recall getting zero reading set at DC mA for output so thought I was mistaken and both tests were to be done on the same DC volt setting, because only then would I get any readings.
But reading through past posts I think it should be DC mA for output and DC volt for balance. I know not to touch A.C. balance as I need a scope.
Either I've gone crazy or my DVM has. Hopefully the latter.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
When you measure the voltage (milli-DC), you are really measuring the voltage drop across a known set resistor tied from the cathode-to-ground. The idle current passed can be related to this voltage drop, by Ohm's Law.To measure the actual current passed, you need to break the connection between ground and the cathode of each tube. Then, insert your DVM probe to complete the circuit.
Edits: 05/15/14
The test points are set up such that 65 65mV equates to 65mA.
Going to get down to some testing this weekend.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
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