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Old 21st July 2013, 09:56 PM   #61
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how would it work with a pentode driver ?
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Old 21st July 2013, 10:16 PM   #62
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You have a PNP or P-CH pentode? Sweet!

Even if we speak the usual N concertina,
unless you strap as a triode, screen current
will imbalance the result.

Last edited by kenpeter; 21st July 2013 at 10:22 PM.
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Old 21st July 2013, 10:21 PM   #63
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pnp bjt's look like pentodes if you look at the curves....
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Old 21st July 2013, 10:26 PM   #64
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Put a pentode or any N there and see what happens.
You need the top to follow the plate, not the bottom.

Else scrap the whole equal impedanace, non-elevated
heater, free ccs advantage, to live again in caves...

Last edited by kenpeter; 21st July 2013 at 10:35 PM.
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Old 21st July 2013, 10:32 PM   #65
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well, ok, since we now have two gain stages of a triode avaiable, maybe ecc99 would do ?
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Old 21st July 2013, 11:04 PM   #66
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You would have to change R1, or (R2 and R3) to keep the cathode
feedback at 1/Mu.

And that probably isn't the right DC bias forECC99 cathode, so you
have to do something more than whats drawn to correct that too.

Last edited by kenpeter; 21st July 2013 at 11:09 PM.
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Old 21st July 2013, 11:17 PM   #67
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My favorite is the Fairchild FPQ1N50 - no longer in production, but I have a stash for purposes like this. It also has low input and reverse transfer capacitance, lower than the IR part Eli mentioned. The Zetex part he mentioned is attractive, but is limited in practical power dissipation to ~1/2 W, unless you glue on a heat sink. I got another part from IXYS when the Fairchild part dried up - a 2A, 600V part. It's not as good as the Fairchild (Crss is good, but Ciss is a bit high at 240 pF).

I haven't been looking lately, as I still have some of the Fairchild parts, but Alpha and Omega is a good vendor of advanced mosfets, and Digikey stocks a fair number of them. It's a good idea to look first at the smallest current parts for a given voltage rating, to keep the die size (and associated capacitance) to a minimum.

Edit - The Alpha Omega part AOT1N60 is better (much) than even the Fairchild part - maybe I'll get me some...

Last edited by wrenchone; 21st July 2013 at 11:25 PM.
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Old 21st July 2013, 11:26 PM   #68
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Quote:
Originally Posted by kenpeter View Post
....more than whats drawn to correct that too.
not sure what drawing...?
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Old 21st July 2013, 11:55 PM   #69
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What drawing? #13...
As for #68, Driving impedance is not equal without 1/Mu cathode feedback
from the drain, to mimic the effect Mu has upon the top side impedance...

But we also know in the context of driven loads that are equal, and a closed
loop: Locally "equal" driving impedance isn't critical to class AB1 operation.
Primitive concertinas that operate half blind certainly do work. Caves or not.
Even the blind side isn't totally blind, once the GNF loop is closed.

The plate load for the second stage should be across VGS, as that gives you
a constant current source essentially for free.

If you choose to do neither, then there is no advantage to the P-CH splitter.
You would have a better choice of easily obtainable MOSFETs in N-CH...

Last edited by kenpeter; 22nd July 2013 at 12:20 AM.
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Old 21st July 2013, 11:57 PM   #70
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Quote:
The Zetex part he mentioned is attractive, but is limited in practical power dissipation to ~1/2 W, unless you glue on a heat sink.
Mouser stocks 2 parts that might be worth a tumble: 532-322400B00 and 532-575200B00.
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