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)
- Thanks everyone, - Alexo 13:12:37 04/27/07 (0)
- Re: Why do I have DC on my cathode-biased input tube's grid? - mikeyb 11:03:35 04/27/07 (4)
- Thanks for the link, but... - Alexo 11:29:36 04/27/07 (3)
- Hmm actually... - Alexo 11:39:22 04/27/07 (2)
- Actually, actually... - Alexo 11:42:52 04/27/07 (1)
- And put in a 200K Grid Leak Resistor (nt) - Chris O 13:02:57 04/27/07 (0)
- Thanks... - Alexo 10:53:27 04/27/07 (0)
- Re: Why do I have DC on my cathode-biased input tube's grid? - Chris O 10:53:20 04/27/07 (3)
- Re: Why do I have DC on my cathode-biased input tube's grid? - Alexo 11:05:43 04/27/07 (1)
- Gah! Errors! See the corrections here: - Alexo 11:07:21 04/27/07 (0)
- Re: Why do I have DC on my cathode-biased input tube's grid? - danlaudionut 11:04:44 04/27/07 (0)
- Re: Why do I have DC on my cathode-biased input tube's grid? - Triode_Kingdom 10:18:07 04/27/07 (0)
- Re: 680 ohm resistor is wrong! - Ralph 09:34:23 04/27/07 (0)