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In Reply to: RE: Odd Voltage Readings On 27s posted by FlaCharlie on September 15, 2016 at 13:38:33
All tubes have some grid leakage current.
The higher the grid leakage current the lower the bias voltage from the battery will be because current is flowing through the 100k grid resistor.
With no current at all flowing through the 100k resistor, there will be no voltage drop.
More current, more voltage drop across the 100k grid resistor.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
One thing that confuses me is that I had the same tube installed previously and it didn't seem to be drawing grid leakage current. Voltage on grids of both 27s were stable and close the the voltage of the battery itself.
What would cause a tube to develop this condition? Is it related to circuit design or operating points?
Is there anything that can be done to reduce or eliminate the problem, other than just using a different tube? Or is it even a problem?
Will adding a grid stopper help?
I don't know why today would be different than yesterday.
I don't know how to answer any of your questions except,
"Will adding a grid stopper help?"
If the tube is oscillating for lack of a grid stop resistor then maybe that oscillation is increasing the grid leakage current. But I don't know, that's just a guess.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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