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Values for OTL totem pole (cathode followers)
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Old 9th November 2007, 10:10 PM   #1
00940 is offline 00940  Belgium
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Default Values for OTL totem pole (cathode followers)

I've this bunch of PCF80 (same as ECF80, 6BL8) laying around and I know some little things can be done with them. Up till now, I gathered some schematics and spent some time understanding them (back to paper since I can't figure how to use tubes models with LTspice). Still, I've been wondering if a smallish headphones amp couldn't be done with those tubes. With two tubes, I can get a triode for gain, a triode as phase splitter. Up till there, I can understand how it works (very basic understanding...).

A long introduction to just say I'm stuck understanding how much power I could get from the pentodes of the pcf80, triode strapped and used push-pull, into 300 ohms. I see that at 120VDC, I won't destroy the tubes if I ask for 14mA. But can I get those 14mA or not ? I've also a hard time understanding how much voltage swing I can get at the output.

I would really be grateful if someone could point me towards references on this (I found a lot of things on tubecad.com but it goes a bit quickly over the "obvious" things a newbie like me is still missing).


Thanks a lot,

Ben.


(Otherwise, i could of course parallel a bunch of triodes as SE cathode followers with the pentodes as sink).
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Old 9th November 2007, 10:41 PM   #2
00940 is offline 00940  Belgium
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edit: here are the curves for the triode strapped pcf80: http://www.tubes.mynetcologne.de/roe..._as_triode.pdf
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Old 10th November 2007, 10:02 AM   #3
00940 is offline 00940  Belgium
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Ok, the PCF80 pentode once triode strapped looks a bit like an ECC81. So, I could do some sims and the schematic below seems to work.

I've just one question: how to properly set C4 and C5 ? Values around 10µF seem ok in sims but I don't trust LTspice too much.
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