I think I need to go back...

[Chuck H]

Indeed! If an AC15 is putting out 15W I'd be surprised. The Marshall 18W!?! Pfffffft bwaahahaaaa....aahhh... Oh... That's rich. Some guys claim twenty or more from a pair of el84's. Maybe Traynor actually did, I'm skeptical but there are guys that have measured it and swear it's true. But in that case you can't hope for any distortion but bad distortion. The crossover line is soooo tender at such low idle, high grid drive that even touching overdrive results in the worst audible crossover distortion. Nah. IMHO el84's sound just fine run in a nominal way as plain ol power tubes rather than trying to eek every possible watt from them like it's some neat trick.

[nickb]

For the homebuilder, it makes no sense to squeeze every watt out of a tube. Partly because of what Chuck says and also because it saves money in the long term. You might as well cough up a few extra bucks for a higher dissipation rated tube that is run well within its ratings and so will outlast a beaten-to-death small guy many times over.

[Dave H]

My 2Xel84 with a Vp of 355 makes about 14W (Dave seems to be the winner for watts s far ) but there's no guarantee that all of the LF watts being measured by Dave and I ever get heard!!!

I cheated The PT is one I had wound for a 4 x EL84 amp and my AmpMaker 18W OT is quite large too. It used to have a much smaller OT and it was only 12W then. I have a 220 ohm resistor in series with the PT B+ winding to lower the voltage. If I short the resistor the B+ goes up to 275V or more and it measures 20W (see below) but the EL84s are idling at 15W. It doesn't red plate because it has a fan but I don't like to run it like that for long (and I'm measuring at 500Hz not 50Hz)

[Chuck H]

It used to have a much smaller OT and it was only 12W then.

Did you notice a big difference in the tone? Loudness? Or just measured watts? Just wondering because of escher's situation. I did build a 2xel84 with a smaller OT (Classic Tone I think), but it wasn't a guitar amp. It was a reverb only amp that filches drive from a host amp. I never measured output and I can't say about tone either. My own amp uses a Hammond 1608 (rated 10W and about twice the size of the 1760e).

[Dave H]

Did you notice a big difference in the tone? Loudness?

The larger OT was louder, more punchy and brighter. I had to reconnect the treble cut control which wasn't needed for the little OT. I think the little one was intended for the 1U rack mount Marshall 20/20. You can see it below. It was tiny, smaller than my 5W SE OT

[J M Fahey]

the 1U rack mount Marshall 20/20.

So it should be relabelled Marshall 12/12?
I guess it should

[g1]

Chuck, you need to listen to some Traynor 6BQ5 amps, many of which are still running power tubes that were installed in the '70s.

[Tom Phillips]

I cheated ...I have a 220 ohm resistor in series with the PT B+ winding to lower the voltage...

That significant bit of information, which was missing from your earlier posts, explains why you are getting the lower power readings. The power amp will sag as the B+ drops under continuous drive conditions. If you like the sound and touch response then all is good and you can just enjoy playing the amp now that you know the reason for the measured power reading.

[Chuck H]

Chuck, you need to listen to some Traynor 6BQ5 amps, many of which are still running power tubes that were installed in the '70s.

Oh, I acknowledged above that Traynor (if anyone) might have pulled it off. I would really like to get one of those on my bench. I've had a couple of Traynors, but no el84 models and none of the other ones that made the crazy wattage claims like 86W from a pair of 6ca7's and such. I'm "told" it's all true. But let's face it, a claim like that needs to be seen to be believed.

[eschertron]

15W .. 18W!?! hahaaaa....aahhh...

So I'm OK with the actual measured power of the amp, because the actual, sensed, loudness of the amp is just fine, 'specially through a nice closed-back 4x12 cab. The fact that it approaches 15 or 18 Watts under full tilt is just fine and dandy.

My initial confusion was that perhaps I was measuring the output power wrong. That's been cleared up.

Also cleared up was my Gross Conceptual Error that I would see output increase up to the input headroom limits. I have played with load lines on resistance-loaded triodes (preamp applications) and have seen how the plate voltage relates to the control grid voltage. I was not prepared to see the plate voltage on the EL84s 'level off' before grid limit was reached. After careful review, I can see that Nick B's tech page is showing exactly that.

Since this amp is an exercise in preamp distortion and is expected to be used at home/coffeehouse/church volumes, the output power assessment is no cause for alarm. I'll have to remember to guffaw next time my buddy explains that his Bugera 22 is a 22W 2xEL84 amp(?!)

[eschertron]

My own amp uses a Hammond 1608 (rated 10W and about twice the size of the 1760e).

I've read that in a previous post of yours, and seriously considered experimenting with some different OTs. Don't know what I'd do with 'em after larking about, though.

[g1]

Oh, I acknowledged above that Traynor (if anyone) might have pulled it off. I would really like to get one of those on my bench. I've had a couple of Traynors, but no el84 models and none of the other ones that made the crazy wattage claims like 86W from a pair of 6ca7's and such. I'm "told" it's all true. But let's face it, a claim like that needs to be seen to be believed.

I understand. Having seen it I'm no longer skeptical (both examples).
I know you do accept the 'power amp as modulator of power supply' school of thought, so that's a good start. They aren't called valves for nuthin' .

[Chuck H]

I've read that in a previous post of yours, and seriously considered experimenting with some different OTs. Don't know what I'd do with 'em after larking about, though.

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