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Old 2nd May 2011, 09:41 PM   #1
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Default Choosing plate voltage

I'm newbie to tube circuits and interested in building tube distortion/overdrive
based on 12AX7 (due to the high amplification factor)
it is easier to choose low voltage (9,12,18v filament will get 6.3/12.6v)

what are the criteria for plate voltage that I should consider?

Thanx,
Sami
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Old 2nd May 2011, 09:53 PM   #2
DF96 is online now DF96  England
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To a first approximation, the lower the voltage the more distortion you will get.
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Old 2nd May 2011, 10:56 PM   #3
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The lower voltage the more distortion, is that due to clipping of lower voltage?
But also the higher voltage the more amplification
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Old 3rd May 2011, 11:42 AM   #4
DF96 is online now DF96  England
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Both clipping and non-linearity. The 12AX7 is very linear when driven into a high impedance load with adequate anode voltage.

Two options: study the data sheet, or try it and see.
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Old 3rd May 2011, 09:00 PM   #5
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What plate voltage would you suggest for this application?
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Old 3rd May 2011, 10:27 PM   #6
DF96 is online now DF96  England
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Sorry, I design for low distortion so I haven't a clue. I'm sure someone will be able to help.
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Old 3rd May 2011, 11:56 PM   #7
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it depends on the circuit. I built a similar OD with a 12ax7 in cascode. My plate voltage was about 125v. It was a litle clean for my liking so i addaed some clipping doides as well. Experiment with low voltages first and see how it sounds.
Best of luck!
Mario.
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Old 4th May 2011, 10:54 AM   #8
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Try running the first half of the ax7 on a high plate voltage (150V or more) for lots of gain, then couple the signal into the second half which you run at a low voltage (50V or less) to drive it deep into distortion.
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Old 4th May 2011, 05:57 PM   #9
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Thanx guys for your answers
if any body has something to add..
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Old 4th May 2011, 09:50 PM   #10
Merlinb is offline Merlinb  United Kingdom
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You may like to look at one of the many DIY valve overdrive pedals:
The Real McTube Article: How It Works

http://www.diystompboxes.com/pedals/.../shakatube.gif

Beavis Audio Research
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