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Can someone explain this confusing schematic?
Can someone explain this confusing schematic?
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Old 14th September 2017, 03:06 PM   #51
smoking-amp is offline smoking-amp  United States
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on the Floating Loyez Phase Inverter idea:

In posts 44 and 46 I made a mistake of taking the floating balancing correction N-Fdbk signal from the top junction of the plate resistors (near B+ with an added series R). This does not produce the correct balancing signal. (although maybe still an interesting one, see below). The balancing signal must come from the junction of two separate high value R resistors connected directly to the plates. Just like is done for typical Floating Paraphase Phase Inverter designs.

The previous near B+ pick-off connection picks up class B like currents from 2nd H distortions within the (individual) tubes. (disturbing the otherwise constant current flow from B+ in nominal class A operation) Called common mode distortion in class A I think, a different amplification problem. This Common Mode N-Fdbk signal could be useful for distortion correction too, but not for balancing. It would have a similar effect to putting a CCS under the stage cathodes.

The correct balancing signal pick-off from the junction of separate high value R's, does also include the common mode error signal as well (any common mode V drop appearing on the plate resistors), so it tends to fix that problem as well. So this balancing signal would also help make the Loyez operate as if it had a CCS tail. (and probably adding a cap time constant back into the response from a V isolation cap in the balancing Fdbk path)

(and thus completing all the surrounding fix-ups to the Loyez to make it act exactly like a Schmidt inverter with CCS tail in the 1st place)

Yeah, the Loyez is just a design exercise. Obtuse.

Last edited by smoking-amp; 14th September 2017 at 03:30 PM.
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Old 14th September 2017, 07:52 PM   #52
Ketje is offline Ketje  Belgium
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Speeking about mistakes, i made some (many ? ) too.But comming across an unusual circuit one learn new things.
Normally a LTP with a resistor on the cathodes is only corrected with uneaqual anode resistors.
Here i got the impression it was done with a correction signal on the normally grounded grid.Looks logical, the cathode resistor prevent a perfect signal transfer between cathodes, so why not compensate the loss with a (small) signal at the what was the grounded grid.
Well that doesn't work.The correcting signal also influence the other triode who sees a smaller cathode resistance, =more gain and both anodes get more signal.The difference doesn't disappear, only gets smaller.
Only when the correction has the same amplitude as the input signal the outputs match.But that we know allready.
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