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RE: "the question is incorrectly formulated"

Just as I have previously stated, what you are referring to is not necessarily related to tube type (pentodes or triodes) but circuitry and operating points.

I am rather familiar with the table you have posted, and it is quite inconclusive and inconsistent. The text from which you have taken it (and thus it is devoid of meaning, while in academic fashion you should have quoted the source and not shown the table, so everyone can read the text and check-out not only the table but the rest of the source as well for context) is mostly trying to show how ultra-linear connection of pentodes (in push-pull amplifiers) leads to a better result than either pentode or pseudo-triode connection (I don't understand why one would call connecting a pentode in triode mode, i.e. tying anode to g2 and thus having the same AC path for both - "pseudo-triode", unless there was some marketing department involved... and marketing/advertising became the great new thing at approximately the same time when this text was originated).

Among other issues shown in this table, the same tubes are obviously operated with different operating points, where some are "pure" class A (or deep class AB), while others are obvious class AB (rather shallow AB, meaning that most useful operation is not class A, i.e. one of the devices is shut off most of the time).

Another issue is that the output power differs, and thus the distortion figures should be appropriately matched to output power - we should also not forget the difference in load! It is not the same whether you operate a pair of EL84 with a common cathode resistor of 150 ohms into 10k, or a pair of EL84 with separate cathode resistors of 270 ohms each into 8k... adding to the disparity of the comparison, triode connected pentodes have lower Ri but are operated into a higher load -- and while doing that, there is no mention of the necessary input swing.

While very interesting from a historical point, as an illustration of times past and the way the industry was managed at the time - the relevance of this text in scientific/academic terms is non-existent (too much inconsistency and lack of method) while the data presented might be adequate at the time, but is rather lacking by todays standards.

An added minus of this illustration is the fact that most have not done enough reading or research in the past to be able to recognize the source of such a table, which makes it totally irrelevant. I guess I don't need to research this topic, but you obviously do.

As for DHTs, please try to avoid further mix-ups of apples and oranges ;) If you are interested about pentodes, DHTs and similar stuff, you might check out my blog for some inspiration.

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http://rh-amps.blogspot.com/


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