Low plate voltage pentode (<40v) for diff pair?

Rescue Toaster · 1st September 2006, 09:02 PM

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.

SemperFi · 1st September 2006, 09:19 PM

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.

Rescue Toaster · 1st September 2006, 09:27 PM

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.

Geek · 2nd September 2006, 12:56 AM

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.

1st September 2006, 09:02 PM	#1
Rescue Toaster diyAudio Member Join Date: May 2005 Location: Wisconsin!	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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1st September 2006, 09:19 PM	#2
SemperFi diyAudio Member Join Date: Jan 2002 Location: nowhere	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.

1st September 2006, 09:27 PM	#3
Rescue Toaster diyAudio Member Join Date: May 2005 Location: Wisconsin!	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.

2nd September 2006, 12:56 AM	#4
Geek diyAudio Member Join Date: Sep 2004	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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