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I always get mixed up between the class A/ class A/B thing (as you said, it's more to do with the "on all the time/not on all the time" thing than push-pull) and single-ended/push-pull. To be fair, it doesn't help that a lot of the marketing, and even supposedly-education articles you sometimes read, act like they're the same thing, when as you said you can have genuine class A operation in push-pull. (I meant to put that in my post but forgot ) )
" Saying that in cathode bias a kt66 is what around 14 watts @ICBM ? "
The HT-20 is EL34s (could prob use a 66?) and uses a combination of cathode and adjustable bias to give just bang on 20 watts and really no more. The all FB rest of the HT range will deliver considerably more whallop than their "number" suggests.
Dave.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I have an irrational perception of EL84s as "low budget"/inferior and 6V6s as "better"/more proper. I don't know why, other than that you tended to find EL84s in budget amps in the 2000s, and also that Fender built all their smaller Hot Rod amps around EL84s rather than the 6V6s of their more expensive and prestigious vintage reissue brethren. All canny marketing, I've no doubt.
I love the sound of my Princeton. Not sure how much of that is 6V6 related. (Because of the knacky custom transformer in that amp, their plate voltages are ~360v rather than the ~440v of the original transformer. Hard to say what the difference in sound is as it was hardly an A/B scenario. ^_^ But it'll certainly be kinder to them over time.)
Outside of guitar amps I was never a great fan of the EL84. Mind you, not much used the E version but you found UL84s in crappy Dansette record players where they did fail quite often (tho' IIRC the carbon 1W cathode resistors used to cook and go low but which failed first?) .
Can't recall a radio that used an EL84 but the earlier ones used 6V6 and were just about bombproof, lasted decades. A few radios used an octal EL32, not THE most reliable valve.
PA amps used KT66, EL34 (and old fairground stuff 807) never 84s. However there was a Philips rack PA amp used for headphone distribution in hospitals and they used EL81s, a 6volt version of a TV line output pentode. They ran at an elevated HT and gave I would guess 40-50watts a pair.
Speaking of "elevated HTs"! There was the EL31, top cap anode and Avon Cosmetics had an amp with a bloody big OPTraff in it and ran at about a kilovolt.
Dave.
The Laney l50H uses 5 el34s for 50 watts - and sounds absolutely glorious for it.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein