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Why do I have DC on my cathode-biased input tube's grid?

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Good morning everyone, here is my conundrum:

I just fired up a build last night, first preamp stage is a paralleled 12AX7, 165 volts B+, 90 on the plate, 120K plate resistor, 680 ohm cathode resistor, 39K grid stopper, 1 meg from grid to ground.

So... it works, I guess, but there is about -.5 volts on the grid, consequently, -.5 volts on ehatever I plug into it. What would cause this? It is very annoying, there is also a good deal of hum coming through, and reduced gain as a result of this weird unwanted negative bias.

Any suggestions? All my wiring seems to check out... what gives?

Thanks!


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Topic - Why do I have DC on my cathode-biased input tube's grid? - Alexo 08:39:54 04/27/07 (13)


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