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Salas 18th March 2009 06:16 PM

Anti-Triode SEPP, how to do best?
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Hi guys

I have made a couple of variable anode CCS sources. One cascode enhancement Mosfet LED biased of mine, and one Jung's LM317 10M45S cascoded. I am running experiments on my 6V6 trioded line pre. My B+ is 330V regulated and there is a capacitor bypassed 680R cathode resistor installed. I measured much better THD at the same bias point where the previous 5K resistive load was sitting (22mA). Sounded dynamic and clean, but in the long run I miss the previous tamer but more natural tone. It got more SS taste, and it got a bit of more hiss on my 95db speakers. When I took it down to 15mA, it backed up on hiss and SS tone, but still the same impressions. I wanna retain the dynamic and THD gains, but bring back some triode tone. I guess that valves can be pushed a bit with anode CCS and hiss if not lower current than previously with resistor is chosen? OK, the Mu is pushed now, but I have got more hiss compared to gain.
It reminded me of when running a noval hotter until it starts to simply hiss. Anyway, that is why I wanna listen to the Anti-triode before I go back to resistor loading. How it can be practically done best? I mean, just put two resistors between CCS and anode, and tap off from the center for output? OK then, is there a formula to calculate, given the B+, freely chosen CCS current, and given Rk as I described above?

EDIT: Here is the chart of 6V6 trioded. Suggestions for anti-triode?

Salas 18th March 2009 07:18 PM

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I understand that the idea is to tap off from the middle point of the current set resistor, but in this source its on top.

Salas 18th March 2009 07:20 PM

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In the alternative one its more convenient, but the problem is that with this one the tubes hiss much stronger.

kenpeter 18th March 2009 09:25 PM

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Nelson's Pass' Aleph may be your best bet.
It can be reconfigured as an MJK Anti-Triode.
Which makes it a lot less complicated than
Nelson's way, and direct coupled as well.

I've omitted the gate pullup bootstrap off the
source of the MOSFET for clarity. But with it,
you can get with within a volt or two of the
upper rail.

10M45S needs 10 or 15 volts standing on it.
Gate capacitance and VGS-ON an unknown.
Other than that, it still seems to work.

Aleph gets around both those issues.

Salas 18th March 2009 09:50 PM

Thanks kenpeter. 10M45S is enhancement mode that includes an error amp so it stays on like a Depletion mode Mosfet. I have to use my IRFPs. Something that bugs me a little is that I have to resort to one Vbe CCS non cascoded. The D.Self bootstrap cap enhances the lot by positive feedback of course. I was hoping there is a clever way with the already made couple of CCSs that I have, but I must draw a new one most probably...

Salas 18th March 2009 10:09 PM

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An idea so to keep it minimal parts count, still cascode, is to make this, measure the trimmer, and then make the resistance needed from 2 half ones and tap for output from middle point. What do you think?

kenpeter 18th March 2009 10:12 PM

Might use a similar circuit inside? They don't say.
Acts like -5VGKon, so it can't be an Aleph emitter
drop. Maybe another enhancement MOSFET?

Aleph is pretty consistent in the emitter coupled
on voltage. And the Base follows the Emitter, so
the impedance isn't real low like you'd think.

I've been playing with it a bit lately. Pretty sure
I'm driving Nelson crazy over on that side of the

Turn his junk inside out and make current mirrors
and other wierd thingies... Off deep end as usual.

Salas 18th March 2009 10:28 PM

Its true they don't say. So maybe I will draw a one Vbe D.Self bootstrapped IRFP9240 source (that's actually an Aleph called source), and tap off from middle of sense (set) resistor. Better on the safe side...What do you reckon?

Wavebourn 18th March 2009 11:28 PM

Here is what works like a charm; actually it is a gyrator. You may use MOSFETs here, or at least one on top to increase voltage divider's resistance and decrease capacitance needed.
It does not provide a constant current on DC. Actually, on DC it provides a constant voltage, but on AC it's dynamic resistance is huge.

kenpeter 19th March 2009 12:01 AM

That is absurdly cool!

I'm sure you've shown it before, but I only just now "got" it.

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