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Old 25th October 2012, 11:17 PM   #1031
SY is offline SY  United States
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Quote:
Originally Posted by CPaul View Post
First, please review p. 1012, which establishes that model 1 in p. 1016 is the same as the model in Figure 3 of your article. (If you disagree, be explicit as to why. Simply saying that models are wrong is meaningless. Wrong? How? Wrong color? Why, are black and blue no good?)
If you look at that extremely complex non-Thevenin model, then look at my very simple (and experimentally accurate) model and think they're the same, you need glasses. Try counting components- mine, two voltage sources, two resistances. Yours, well, you can count.

The other, simpler models you presented, which I already cited to you, are not the same as mine because they give totally wrong answers for the output voltages.

I think I'll tip my hat at this point and say, "Adieu" until you experimentally show that my model, under the given constraint, does not agree with experiment. Fume away.
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Old 26th October 2012, 02:05 AM   #1032
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Driving a push-pull pair of 6L6 into A2 open loop with equal and unequal
models was sufficient challenge to satisfy that both models produce very
nearly the same end result. Any model that says otherwise probably isn't
relevant to the need for this sort of phase splitter anyway.

Cap pumping was the killer, not the subtle effect of huge differences in
AC impedance. Chasing our tails around ridiculous proofs for nothing.

Last edited by kenpeter; 26th October 2012 at 02:08 AM.
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Old 26th October 2012, 02:45 AM   #1033
AJT is offline AJT  Philippines
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Quote:
Originally Posted by kenpeter View Post
Driving a push-pull pair of 6L6 into A2 open loop with equal and unequal
models was sufficient challenge to satisfy that both models produce very
nearly the same end result. Any model that says otherwise probably isn't
relevant to the need for this sort of phase splitter anyway.

Cap pumping was the killer, not the subtle effect of huge differences in
AC impedance. Chasing our tails around ridiculous proofs for nothing.
my impression too of this thread.....
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Old 26th October 2012, 03:27 PM   #1034
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I find SY's reply inscrutable.

Quote:
Originally Posted by SY View Post
If you look at that extremely complex non-Thevenin model, then look at my very simple (and experimentally accurate) model and think they're the same, you need glasses. Try counting components- mine, two voltage sources, two resistances. Yours, well, you can count.
What complex model? model 1 is SY's model, model 2 adds one resistor to it, and model 3 subtracts a ground from it!

Quote:
Originally Posted by SY View Post
...non-Thevenin model...
Another SY special: unfounded assertions again. What's non-Thevenin about it?

Quote:
Originally Posted by SY View Post
The other, simpler models you presented, which I already cited to you, are not the same as mine because they give totally wrong answers for the output voltages.
Unfounded assertions again! This time, in the face of simulations which clearly disprove the claim. Where is the support for "totally wrong answers"? What are the salient differences between the sims I presented and the test results in SY's article?

Quote:
Originally Posted by SY View Post
I think I'll tip my hat at this point and say, "Adieu" until you experimentally show that my model, under the given constraint, does not agree with experiment.
If after all this time you think I've been challenging your experimental results, you need a semester or two of reading comprehension drills. I challenge the conclusions you draw from a model that are impossible to test given the constraints you have imposed, never your test results. You don't get to exit as cleanly as you hoped.



We have reached the point where we now are living in different realities. Not only do we get unsupported claims, but we are getting ones which seem to defy what is right before our eyes. If no one who has been following this exchange can explain to SY and me each others' fundamental perceptions, then further communication on this topic is indeed useless.

I'd welcome anyone who has been following this exchange to step forward at this point with constructive explanations to one, the other, or both of us.
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Old 27th October 2012, 04:14 PM   #1035
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Quote:
Originally Posted by CPaul View Post
I find SY's reply inscrutable.

We have reached the point where we now are living in different realities. Not only do we get unsupported claims, but we are getting ones which seem to defy what is right before our eyes.
Just because his definition of impedance includes anywhere from 1 to 99%
cross coupled arbitrary noise. By pure coincidence, usually but not always,
happens to quack so muck like impedance, its own mother would not know
where real impedance ends and noise begins...

You seem to forget: Sy's absurd claims are supported, "Because I said so."
Also because the A2 load experiment proved so. No other reality matters...
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Old 17th December 2012, 02:07 PM   #1036
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Time for me to sum up and put a coda on my posts to this thread. (And there was much rejoicing!)
I built the following familiar circuit and drove its grid with a square wave having a 30mV step:
Lascas.GIF
I also measured the parameters gm ( 8.83mS ) and µ ( 27.6 ) of the triode under the circuit’s operating conditions. I used them in the following analytic expression and models, all of which were developed to predict the plate and cathode voltages of the physical circuit:
lascas2.GIF
The outputs of the circuit, expression, and models appear in the following graph:
lascas3.GIF
Clearly, the all-around agreement is excellent, validating the expression’s and the models’ voltage predictions. Not so much so with the models’ predictions of the low frequency P and K to ground impedances Zpg and Zkg though – in fact, they contradict one another, with values of approximately 1/gm for Model 1 and R/2 for Model 2. Obviously, at least one of the models gets it wrong. And since that one got the voltages right, we have proof that getting the voltages right does not ensure doing so with the impedances. Therefore, there is no reason to believe that either one of them gets it right. So what to do?
Check out the next post!
Attached Files
File Type: asc lascas.asc (3.7 KB, 7 views)
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Old 17th December 2012, 02:11 PM   #1037
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Because there has been some controversy regarding the Thevenin theorem in this thread, I’ve turned to the folks who arguably are the ultimate authorities on this matter: The Institute of Electrical and Electronics Engineers. They publish The new IEEE standard dictionary of electrical and electronics terms. In it can be found the following:
Thevenin’s Theorem. States that the current that will flow through an impedance Z’, when connected to any two terminals of a linear network between which there previously existed a voltage E and an impedance Z, is equal to the voltage E divided by the sum of Z and Z’.
Here we have a simple method by which we can determine the impedance between “any two terminals of a linear network between which there previously existed a voltage E and an impedance Z”.

Certainly the Cathodyne can be considered to be a linear network, and among its several “any two terminals” are the plate and ground. When we apply Kirchoff’s laws and Thevenin, it’s trivial to derive
Zpg = [ Rk· (1+µ) + µ/gm ] || Rp
If instead we choose the cathode and ground as the terminal pair, we get
Zkg = Rk || [ (µ/gm +Rp)/(1+µ) ]
Finally, for the plate and cathode, the result is
Zpk = 2/gm / [1 + 2/µ + 1/(gm·R’)] ≈ 2/gm, where R’ = Rp = Rk
There are several take-aways from this:
1. Mr. T. deals with two nodes, not three (P and ground for instance, not P, K and ground);

2. There is no need to keep a balanced circuit balanced while measuring its impedances, and

3. Zpg and Zkg are quite different indeed. In particular, Zkg is just north of 1/gm, while Zpg ≈ Rp >> 1/gm.
And that’s all that needs to be said on the matter.
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Old 13th January 2013, 04:19 PM   #1038
piano3 is offline piano3  United Kingdom
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I was thinking of simple ways to interface my single-ended CD player with my totally differential main system; is there any reason for not using a concertina phase-splitter with(necessarily) low values, 1k5 say, of R anode and R cathode assuming that the high tension is decoupled with a suitable RC network?
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Old 13th January 2013, 07:01 PM   #1039
piano3 is offline piano3  United Kingdom
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Actually, that is probably a pretty stupid idea, even considering the feedback; better to use an input coupling cap.
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Old 13th January 2013, 07:18 PM   #1040
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For the A and B differential inputs of your system, what are the impedances between:

A and B;
A and ground;
B and ground?
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