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Old 1st September 2006, 09:02 PM   #1
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Default Low plate voltage pentode (<40v) for diff pair?

I need to make a diff pair that runs at no higher than 40v plate to cathode. The CCS below them goes to a negative voltage, but the plates cannot be higher than 40v, obviously the load resistors go to a higher voltage, and the screen voltage can be regulated to any value. (150? 200? doesn't matter)

I don't actually need much gain (5-10 will be fine) so load resistors and B+ will be chosen appropriately. Of course, something low distortion that might sound good would be ideal

I know of those space-charge tubes (generally run at 12-15 volts plate), but they don't seem very linear.
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Old 1st September 2006, 09:19 PM   #2
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I don't know if pentodes run well at 40volts, but if you only need a gain of 5-10 then why a pentode? 6922 runs ok at low voltages, but it is merely a triode. You say you have higher voltages available for the screen, so why not for the plate? Are you DC-coupling to the next stage?
Btw, the screen should not be at a higher voltage than the plate.
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Old 1st September 2006, 09:27 PM   #3
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Yeah, it's DC coupling to the next stage.

That's also why pentodes are required, as you can adjust the source voltages to trim out DC ofset at the output.

The 40 volts was chosen because it's possible the user COULD be exposed to this voltage (unlikely, but possible) so it can't be at a dangerous voltage.

I guess if there's no way to get there with tubes I'll have to go to mosfet.
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Old 2nd September 2006, 12:56 AM   #4
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I have heard of people using the screen as the plate at those voltages, but dunno the linearity or have any experience with it myself.
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