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Old 7th October 2012, 09:55 PM   #971
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Except for your data, which agree with that conclusion as long as you kept the loads equal. It's the very symmetry you deride which causes this useful behavior, the exact canceling of plate and cathode signal currents to ground. Everything you saw (and I congratulate you for actually building and measuring something!) is consistent with Figure 3 (the two Thevenin source model) in my article.

The absence of ground current is a feature, not a bug.
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Old 8th October 2012, 01:27 PM   #972
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Were that I could applaud you for engaging in analysis.

Here are some of the multiple models that your and my experimental data simultaneously support:

cdyne4.GIF

Except for the one on the left, they are all inconsistent with your Figure 3 & 2.

You have offered no experimental verification of your conclusion that Zpg = Zkg = 1/gm. Your experimental data do not lead to the determination of R? at all. This is why BV's floating source explains balanced Cdyne operation as well as your grounded ones - because balanced Cdyne operation in no way constrains or determines the value of R? in your models.

With the high position that experimental verification occupies in your toolkit, you should be able to come up with an experiment to refute the assertion that R? is, oh, I don't know, 1537 ohms. Can you?
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Old 8th October 2012, 01:35 PM   #973
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Quote:
Originally Posted by CPaul View Post
Except for the one on the left, they are all inconsistent with your Figure 3 & 2.
If they give the same predictions, then they're consistent. The one on the left actually represents the way the circuit is used so is probably the best to use for those who design and build amplifiers.
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Old 8th October 2012, 01:39 PM   #974
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So you can't design an experiment to rule out the possibility that R? is 1737 ohms?
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Old 8th October 2012, 01:46 PM   #975
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Originally Posted by SY View Post
If they give the same predictions, then they're consistent.
But they don't give the same predictions for Zpg and Zkg.
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Old 8th October 2012, 03:07 PM   #976
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If the loads are the same (edit: and they each go to ground as in Figure 3 and every amplifier application I'm aware of), yes they do.
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Old 8th October 2012, 03:50 PM   #977
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R? can be anything, regardless of the values of the matched loads, and still predict balanced Cdyne performance perfectly.

And if R? can be anything, so can Zpg and Zkg.

It can't get much simpler than this.
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Old 8th October 2012, 04:37 PM   #978
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If you consider the ground resistance part of the load (the load measurements ARE ground-referenced), then 1/gm is still the right answer. What happens when, as is the case where this circuit is used, the following tubes have an input capacitance of Cin referenced to ground?
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Old 8th October 2012, 05:50 PM   #979
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Quote:
Originally Posted by SY View Post
... 1/gm is still the right answer.


So then, BV's model is wrong?

By definition, in a balanced situation, with or without capacitive loading, the voltage in the center of the model is 0V. There is no potential difference across R?; no current flows through it regardless of its value. If there were a difference, the circuit wouldn't be balanced.

Since no current flows through it, the circuit cannot possibly be measuring it. If it is not being measured, it is unknown to tests constrained by balance in the Cdyne. Since R? is clearly a part of Zkg and Zpg, they are also unknown.

If you are referring to the square wave test in your article with matched R-C loads on the P and K, the 2/gm impedance between the P and K explains things perfectly. Imagine BV's floating source of impedance 2/gm presenting a square wave. The P & K voltages are equal and opposite, and the time constant is gm/C. His model achieves this with a value of R? = ∞, as does yours with R? = 0, making my point.

There is simply no experimental evidence to support the claim that Zpg = Zkg = 1/gm.
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Old 9th October 2012, 02:58 PM   #980
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The global loops are now open. Operating points and input levels
normalized for same full scale output as previously given example.

I really expected unequal impedance (while driving A2) to be far
and away inferior to the equal impedance model. In practice, the
equalization of Z's made measurable but insignificant difference.

Is transformer splitter (DC crutch) invalidating the Concertina test?
True, but 7.5X more AC current does take cap coupled paths. So I
would expect some Concertina model validity to survive? I'm just
not seeing damage of the sort I surely imagined would be there...

We are driving A2 current swings to the Concertina quiescent limit.
Under these brutal non-linear load conditions, it should matter a lot.
So why here did it matter so little?
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Last edited by kenpeter; 9th October 2012 at 03:11 PM.
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