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I measured one and got clipping at about 22W, not surprisingly. And even that’s really hammering them on the plate voltage.
Still, if all the solid-state companies are using output ratings that exceed the power draw now, maybe it’s just playing catch-up...
"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 mean, yeah, if you use meters and science and stuff, it's a bit of a stretch - but if you whack the amp up full blast, get a mate to stand at the back of the room while you knock out a few Malcolm Young riffs and shout, "HOW MANY WATTS DOES THAT SOUND LIKE? TWENTY-EIGHT?" ...and he nods - well, you're in...
My guess is that MESA would have got more output power if they had increased the loading. Most manufacturers simply use the "correct" value of 8k for 2 x EL84s.
Peavey got 50W from 4 x EL84 in the Classic 50 (ie 25Ws per pair), and I've measured a shade under this in a Traynor running 420 VDC on the HT.
It can also depend on the valves - my Mesa DC-5 went up from 50W with the stock Chinese 6L6s to over 60W with some NOS JAN/Philips 7581As - which are still technically '6L6s', just very good ones.
"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
Personally, I hated it - shouty and overbearing in front, muddy and indistinct off to the side, and no real bottom end. The F-50 - which was a real 50W - was just better in every way, although admittedly heavier and more expensive.
"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
In fact, some Hifi guys are getting 35w from a pair of EL84s - http://www.ramlabs-musicreference.com/rm10mk2.html
That's 35w per channel (2xEl84) or 70w Mono. Think it runs 700v on the anodes and 350v on the screens.
My favourite tool for designing output stages shows 32.5w in real world conditions - http://bmamps.com/Tech_tds.html
Va-k - 400V,
Ra-a 8k,
Vg2 - 380V
-20V grid bias
PD at 12w-ish
Yes, you'll need a 40v pk-pk input to achieve, but it's not impossible.
Rift Amplification
Brackley, Northamptonshire
www.riftamps.co.uk
The rule of thumb maximum output for valves in push-pull is 4 X pa which gives 48W for the EL84 so in theory, ~30W is possible but, although the data shows a pair of EL34s CAN deliver 100W I doubt anyone has tried?
Re, power measurement: Minefield, we had all this swaddling when transistor PAs came out because they were feeble compared to valves and the makers had to 'massage' the figures. Thus a 5W pch ICE amp becomes a 50W "total, instantaneous, peak, music power" monster!
For valve guitar amps I cannot see any problem in specifying Pout at 10%thd? That is after all the thd most often quoted in valve data sheets. A 50W guitar amp is for instance SO loud through a 100dB speaker that is would not be AT 50W and 10% thd for more than mSecs and thus never be a problem. For super loud, super cleans, maybe.
Forgot. Yes DJH, modern KT88s are not as strong as they once were!
Dave.
Largely marketing bullshit, as Collings said.
I have to say I always ‘tame things down’ if possible - reliability is far more important than squeezing another dB or two out of an amp. If you really need more power, you just need a bigger amp.
"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
Musicman managed to get very high outputs from pairs of either EL34s or 6L6s running pretty much in class B with high anode voltages. I've regularly measured around 80W in these amps.
A major concern in guitar amps running EL84s so hard would be that they are often driven hard into clipping, even at "modest" volume levels, and this is very hard on the valve screens, especially if you have increased the loading to compensate for higher anode voltage.