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12AT7 for 12AX7 in preamp
12AT7 for 12AX7 in preamp
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Old 11th February 2019, 05:14 AM   #21
TonyTecson is offline TonyTecson  Philippines
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12AT7 for 12AX7 in preamp
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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Old 11th February 2019, 09:24 AM   #22
awkwardbydesign is offline awkwardbydesign  England
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Originally Posted by TonyTecson View Post
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...
Thanks. I've downloaded it; I'll see if I can make sense of it.

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Originally Posted by nigelwright7557 View Post
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 !
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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