Watt Sucking Fireball Series

[kenpeter]

Oh? JC = John Curl! Delayed realization...

[kenpeter]

So, anyways, I see Roadbagger already has AX7's on the bottom, and AV7's on top.
This mismatch is a very good if you are driving a grid into A2 that needs pullup grunt
more than pulldown.

But this same mismatch of slew capability could behave very weird if driving Schaded
FET (Translate "Original Zen" for Zenmod) Triode emulator with a big capactive gate,
Schade (fake Mu feedback from the plate) prefers driven fed from a fixed symmetrical
impedance. Symmetry of slew capability into the next stage can be put to advantage
in such cases (and others), and is not an option to be dismissed lightly!

But lets take SRPP one step further, replacing our top device with a BJT "ring of two"
or BJT+MOSFET "Aleph" style current source. Basically a fake depletion mode device
with very high transconductance follows the voltage of the lower, plus a fixed voltage
offset. The SRPP resistor sets the quiescent current, nothing changed about that...

Load tapped up the top of SRPP resistor, this drives nothing like a real tube anymore.
You gots waaay too much pullup, and still no better pulldown. At the bottom end of
the SRPP resistor, behavior dumbs down to a simple CCS. And here, the triode's plate
gets no power steering assist whatsoever...

But right in the middle (assuming the top follower impedance is pretty near zero),
you got this magic node where you get exactly the same assist as-if you had
another virtual Triode in parallel. Even if the device above isn't a triode, it now
forces itself to become one! But since it must fake this from the other side of
push-pull, its actual behavior is not that of a follower, nor is it complimentary,
but that of a true anti-complement. An Anti-Triode emulator...

A vacuum triode need not be anywhere present to make productive abuse of
a circuit with this behavior (again, see Aleph if anyone doubts). Sorry all the
Nelson Pass ref's. Not one to be accused of following the Curl Camarilla, I try
to translate into Zenmod-eese for the as-yet Anti-Triode challenged...

Same thing only different. Other side of the sand/glass curtain. And all that...
Tar and feathers are the only crucial components.

[Zen Mod]

[kenpeter]

Lemme see if I can dumb it down to a picture...
R1 and R2 would be approximately the same.

This should drive the next stage more like a pair
of 12AX7 in SE parallel would. Not as-if push pull
or SRPP... This is how an anti-compliment works!
Insultramentary my dear Watson...

Abused MJE350 to mismatchify the upper device.
Without it, the "midpoint" might have been hidden
inside the upper Triode's cathode resistance where
we can't easily connect.

Any circuit that acts like a depletion mode will do.
More then one way to skin a cat...

[kenpeter]

And regarding AV7's atop AX7's, does this achieve anything stacked AX7 could not?
I mean, you are having to cut back bias current on the AV7 to the limits of the AX.
If you can't slew down any better for it, does it "lower the impedance" or anything
else??

Even with theoretically infinite Gm above, you can't symmetrically slew any better
than 2x what the lower tube alone can do. And makes no sense to chose any "help"
ratio bigger than 2:1, due the limit of pulldown current. Your Anti-Triode help ratio
is high as the SRPP resistor vs cathode follower resistance allows, but is it REALLY
able to give the help you have asked of it, or already over the 2x hedge and into
the la-la-land of asymmetrical impedance?

But you might could fix either situation by paralleling a CCS with the lower triode.
But then, would we lose our minds and want that current source to become yet
another parallel helper too??? The Auntie of Anti is another emulator... Etc etc...
Where does it all end???

And what of the SRPP drive totems in the WSFB??? What is thier "help" ratio?
Are they driving anything (like a grid in A2) that wants or needs the asymmetry?
If no, then why tap the top end of the SRPP resistor? Was that the best tap
point you could possibly have chosen? I'm not saying for sure it isn't, just that
its maybe worth asking the question.

[kenpeter]

And before pointing out the fact I've also tapped the top end in my Differential
White Cathode Follower. That actually was about as close to the middle of the
SRPP resistance (counting the cathode) as I could get. So sometimes the top
is the middle, or sometimes close enough, but not always...

Abusing high Gm on top takes a lot of the mystery out of where the middle lies...

[Roadbagger]

Apparently, judging from the above, the concept was missed here, and since a picture is worth a thousand words, here is what's really going on with the front end. Maybe less coffee would help............

[Roadbagger]

The 1-1AMP preamp was shown earlier in its simplified version, This is the test unit. In answer to request offline

[kenpeter]

Originally Posted by Roadbagger

Maybe less coffee would help............

Rfeedback and Output should both perhaps be tapped at the SRPP midpoint?
This would yeild the highest possible slew rate that could still be symmetrical.
Where within the SRPP resistor is this midpoint? Don't rightly know the cathode
follower resistance of an AV7 off the top of my head...

The real difference is when driving a challenging load. An SRPP with symmetry
of slew might only attenuate the signal. An SRPP without slew symmetry will
almost certainly distort, and possibly even rectify DC. Maybe you get away
with it because you have loop feedback? Or maybe your load isn't challenging
enough to reveal the issue? But is it really ideal to lean upon a loop to fix an
error that doesn't ever need be created in the first place?

Better to lean upon coffee.

[Roadbagger]

This design provides a low plate load impedance for the dual triode differential stage to the effect of removing the miller feedback to this pair. The following stage is what is normally referred to as a transimpedance amplifier, current in and voltage out. The approximate 2:1 difference in the device Gm of this "op-amp" pair linearizes the stage gain and slaves the Ib of the lower triode allowing some gain modulation of the upper current source. I think you may not see the vast dissimillarity between what you keep referring to, and this circuit. There is little frequency limiting here or distortion overall. The intermod performance here is down near -90 to -100 db. Though I happen to be a proponent of zero feedback amplifier topologies, there are some chains of gain that, when locally Gain confined, maintain transient response linearity indemic to the stage being fed back. "You loose nothing, you gain precision". The only "challenging load" in an amplifier should only be the final transducer commonly referred to as a speaker. That part is far removed from this discussion.