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Balance in CCS Long Tailed Pairs

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#101
OMG ! I missed this wonderfull thread and I've just read it back from the start with complete agreement with SY.

Now, what about using pentodes to obtain more gain (more drive) without any additional stage ?
The offender is that "shitty" screen current wich does not participate to the output voltage while it passes trhu the CCS and may unbalance the whole thing . . . at least until you read the Franck Blöhbaum 'Best Pentode" paper in Linear Audio. :up:

Then you can use pentode LTP PI without adding some form of (un)balance adjustment . . . Problem solved 😀

Yves.
 
#102
Tektronix used pentode LTPs all the time. As long as you stay out of saturation, screen current is pretty much linear with plate current, so it balances out and nothing happens.

And when you hit saturation, cathode current essentially remains constant, which might actually be an advantage for clipping recovery -- the extra current being sunk from the screen. Even so, an LTP can easily be made so it "never" saturates.

Tim
 
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