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RE: LTP VS Differential Amplifier

"So the basic issue seems to be that treating it as a grounded cathode and a grounded grid seems to be improper. I don't see treating it that way when the diff amp model actually seems to give the correct output predictions with grid No.2 signal counted as zero."

In Crowhurst's Fig. 626 it is manifest that V1 is driving into the cathode of V2, and since the grid of V2 is grounded, that means that V2 is by definition a grounded-grid amplifier. I don't see that there is any room for that statement to be incorrect.

It may be that one could find some other words to describe the same situation, but they must, logically speaking, be equivalent words describing exactly the same situation.

In any case, whatever words one uses to describe the circuit, there can really only be one set of correct equations that can be written down for the small-signal analysis, and so only one correct prediction for the two signal outputs. The physics, after all, is what it is, and all that is really being done is to apply Kirchoff's law to the currents at each node, employ Ohm's law to relate potential differences across resistors to the currents flowing through them, and employ the small-signal analysis of how the tubes behave under small perturbations around the quiescent conditions. All of these are universally agreed.

There shouldn't really be room for there to be any differences of opinion about what the correct system of equations to describe the circuit should be. And it is a very simply circuit. I think that analysis of Crowhurst's, after correcting the obvious algebraic mistake, is valid.

By the way, what do you mean when you say "the diff amp model actually seems to give the correct output predictions with grid No.2 signal counted as zero"? Correct as judged how?


Edits: 06/18/21
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