SET Asylum

RE: Parallel tube plate inductors?

76.22.120.252

In Reply to: RE: Parallel tube plate inductors? posted by drlowmu on March 05, 2008 at 15:51:54

I believe Jeff implicitly when he describes what he hears as a result of his experiments, but there is an engineering error here I feel obligated to point out:

Two tubes in parallel will of course provide twice the current to the output transformer primary. Reducing the primary impedance to half the single tube value means 0.707 times the turns ratio if secondary (speaker) impedance is held constant. Twice 0.707 is 1.414, and the output current is 1.414 times as great as with one tube. (The output voltage is also 1.414 times as great, giving - of course! - twice the power.)

If you will do me the same honor of believing I hear what I say I hear, I must say the parallel SETs I have heard have all suffered some degree of "smearing". I find it a much less audible fault than those of push-pull, but that's entirely subjective - anyone may disagree with my blessing. Whether this "smearing" is due to imbalance, parasitics, oscillation, or green-faced gremlins with claws is an engineering judgment I am not prepared to make.

The Radiotron Designer's Handbook 4th edition has a few interesting paragraphs on parasitics and oscillation, for those who are interested. I doubt it's the last word though :^)

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