• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

12AT7 for 12AX7 in preamp

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awkwardbydesign

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Joined 2005
TonyTecson said:
Hi, i would suggest that you consult the RCA tube databook, RC30 and look at the tables on RC couples mplifiying stages, those tables contain values of plate load resistors , grid resistors and cathode bias resistors for a give B+ and voltage gain...
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Thanks. I've downloaded it; I'll see if I can make sense of it. :confused: :D

nigelwright7557 said:
I have never got on very well with 12ax7's.
Always ended up using a different model like the 12au7.
It seemed to be more stable and less noisy.
I have used 2 12ax7's halves in series and the tube just fed back on itself.
When I look around there seems to be plenty of amps with the halves in parallel, maybe they found the same problem ?
Having said that 2 12ax7 halves in series is around 10,000 gain so not surprising it was unstable !
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You may be right, and it has more gain than I need, but I don't have the experience (knowledge) to change things by myself.
 
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