Are you kidding me!? Really!?

[Wilder Amplification]

This just in from the Eurotubes site -

"10/21/10 - A little over a year ago we asked our good friends at JJ Electronic to build us a low power EL84 and they agreed to do it! It's not an easy task to build a tube that has never been built, but JJ has proven they are the people to do it. We have been testing different revisions of the brand new JJ EL844 since January of 2010 and it is ready!

We talked about several tubes that would be welcome additions and we have to tell you, JJ has been VERY busy! We are really happy with the way the EL844 has turned out! It's a wonderful sounding tube and will dissipate right at 9 watts rather than 12 watts which will be a great option for players who want to get to the sweet spot at a little lower volume.

Really!? Since when does the rated plate dissipation of a tube govern the output power it's capable of achieving in a given amp circuit? Last I checked, P = V^2 / Load Impedance (nothing in that equation about the "rated plate dissipation of a tube") and plate dissipation governs the minimum safe load impedance you can run at a given B+ voltage. Yes these parameters do affect output power but...he's basically saying that by simply dropping the rated dissipation of the tube itself that that's somehow going to drop the amp's output power and give breakup at a lower volume???

For the record all that's gonna do is cause some BIG overheating issues in EL84 amps...NOT "drop the amp's output power" like he's thinking. Just goes to show how much he DOESN'T know about tube amps...I swear this guy is like the Aspen Pittman of JJ. After all the misinformation in his marketing tactics, why would anyone want to buy from this guy?

[Steve Conner]

Gimme that sucker, I'll "test" it

[Alex R]

"All valves burned in on our special rig" ;-)

I'm finding it a bit hard to imagine how Eurotubes instigated this new manufacturing venture on the part of their suppliers. Maybe it was like...

"Hey Vaclav, we're thinking we need a new type of EL84, kind of less powerful than the ones you make now, like weaker and punier and just sort of generally not so good."

"You mean, from the reject bin you want them?"

"Well, not exactly..."

"Or like an EL83 you want?"

- and so on.

Hey it looks like some German supplier has a direct line to JJ product development also:

Tube-Town Online-Store - NEU ! JJ EL844 jjel844

[Alex R]

Getters look different, plates similar. Ah well, who know, not me that's for sure.

[Steve Conner]

All valves burned OUT on our special rig here

[Robert M. Martinelli]

Gimme that sucker, I'll "test" it
[ATTACH=CONFIG]11380[/ATTACH]

Hi Steve!
Did you mean "Test" or "toast"?

Cheers

Bob

[Steve Conner]

Test, toast, same thing... I guess the B+ is a bit too high since I changed to a solid-state rectifier.

The screen voltage on this amp is variable. I turned it all the way up for the photo, but I usually run it just about two-thirds. So don't worry, the plate doesn't glow like that in normal use

To me it seems that power scaling techniques like that make more sense than swapping in a weaker tube. But Eurotubes sells tubes, and a tube replacement is an easy, convenient plug-in mod.

[MWJB]

Jon Wilder wrote: "Since when does the rated plate dissipation of a tube govern the output power it's capable of achieving in a given amp circuit?"...is this a joke, are you teasing us? ;-)

It may not follow to the last % but that is probably in line with manufacturing tolerances, but in fixed bias, class AB (with adequate plate voltage & transformers, circuit allowing) it is generally the "rule of thumb", at least at the higher end of the scale. Many designers don't seem to feel that amps sound their best at max power output however. So I would expect the 9W JJEL844 to have lower ceiling of clean headroom that the regular 12W tube.

Yes power (measured, rather than potential) is V^2/load impedance...but it only tallies with max output if the amp is designed that way in the first place.

However, as you say Jon, I don't actually know of many amps (if any) that allow a EL84 type tube to idle at less than 10W (without plate voltage rising, defeating the object somewhat in the process)...so the application for this tube would seem limited? That said, many EL84 amps already run their tubes well over max idle dissipation, even in fixed bias and a tube's longevity is in part determined by how hard it is driven, so it's possible that even the 9W tube run at over max dissipation could be useful to home pickers/apartment dwellers who aren't going to drive it intro redplating all the time? I guess the situation is similar to owners of 50W+ amps who want to run vintage 23W 5881, you might bias cooler & accept a slight drop in headroom compared to true 30W 6L6GC or 7581A?

Admittedly, I think the message can be easily misconstrued by the layman and amp owners should have their amp/application evaluated to see if the tube is a good match. Nevertheless, I don't think that Bob Plekta is clueless, I'm sure he has done some homework on this & he does have a lot of practical experience with JJ tubes. Even if this tube was "created/sorted/reclaimed from the reject bin" at his instigation, JJ will ultimately make it available through all their outlets, so I wouldn't be surprised if dealers in other countries are stocking the tube.

[Steve Conner]

you might bias cooler & accept a slight drop in headroom compared to true 30W 6L6GC or 7581A

That's what Jon is trying to get at. Biasing cooler gives you MORE headroom, all other factors being constant.

[MWJB]

Yes, but "all other factors being constant" really means using the same tube in both scenarios, if the EL844 can't supply the sonic headroom, but it can still take the voltage, it is still making less clean power. Likewise, if you have a 6L6 amp that runs late 400's but can take 6V6, the 6V6s will be biased cooler & run at higher B+ due to lower current draws, the 6L6 will run at lower voltage (assuming both biased to a similar % disipation) but as long as that drop isn't too dramatic, the 6L6 will still have better headroom & more clean WRMS.

[Wilder Amplification]

That's what Jon is trying to get at. Biasing cooler gives you MORE headroom, all other factors being constant.

Exactly! Biasing cooler reduces the power amp's input sensitivity (i.e. "gain") which makes it so that you have to push the preamp/phase inverter (where applicable) harder to drive the power amp to full output. This means the power amp will have MORE headroom...not less.

According to Eurotubes's literature they're made to get earlier POWER TUBE breakup. However, if you're having to bias them colder which increases the headroom of the amp, then how are you supposed to get the power tubes to break up "earlier" if you're having to push the preamp harder to even get the power amp to the onset of clipping?

Furthermore, with the lower dissipation rating, how is it gonna be able to safely operate into the same load that was spec'ed for a tube with a higher dissipation rating? Of course like MWJB stated this would probably require a trip to the tech to find out what your load impedance actually is to see if it's too low for the lower dissipation tube....

But in no way will changing JUST the tube's rated dissipation change the output power that the amp is capable of putting out. It will only change the environment in which that tube can safely operate.

My original point was to state that it's been a long held myth that "power is in the tubes" when tubes are just a "voltage actuated current control valve" that controls current to the load. How much actual average power they dissipate when performing this task is governed by the B+/load impedance combination (i.e. the "load line") and the dissipation must be rated for at least this average power to safely operate in that environment.

[MWJB]

Power is universally rated as clean W RMS, so if you fit a significantly less powerful tube to a circuit, even if the plate voltage rises by a few volts due to reduced current draw, the amp will make less clean W RMS (maybe only a little less). However, few EL84 amps are designed to exploit maximum clean W RMS & I have very little interest in W RMS, other than as a diagnostic reference point...as long as your amp sounds good at the power output you run it at, and is at least ball-park in terms of output, anyone should be happy.

If we're talking about existing amps primary-Z is already decided & is really a moot point, unless alternative taps can be utilised.

[Wilder Amplification]

Power is universally rated as clean W RMS, so if you fit a significantly less powerful tube to a circuit, even if the plate voltage rises by a few volts due to reduced current draw, the amp will make less clean W RMS (maybe only a little less).

Yes but this has to do more with the plate characteristic curves than it does the plate dissipation. In the marketing literature, it specifically states that these new tubes will be a "9 watt dissipation tube instead of a 12 watt dissipation tube". That directly refers to the plate dissipation itself, which has little to nothing to do with the plate characteristic curves. He makes no mention of the curves at all...only the dissipation itself.

For the record...the screen voltage controls where those curves are anyway so why not just lower the voltage to the screens like lots do with power scaling?

[MWJB]

If it is a 9W tube, then it can't make 12W clean, irrespective of curves. A 12W tube can make 9W clean but not the other way round. A pint pot can hold half a pint, 3/4 of a pint, but not a gallon.

The load lines point to ideals, but graphs & data sheets are bits of paper and the amps that these tubes will be used in already exist, they don't know about load lines & data sheets, the vast majority of amps using a given tube use more, or less the same primary Z, irrespective of B+...they probably won't realise the full potential of either tube due to shortfalls in design (as regards power, guitarists buy amps because of what they sound like)...looks like someone is going to have to buy some EL844 and A/B against EL84...

[Wilder Amplification]

If it is a 9W tube, then it can't make 12W clean, irrespective of curves.

OK then...explain how a pair of 35 watt dissipation tubes can make 100 watts clean power.