6L6 SE Amp with 20 Watts?

[rexindigo]

Hi Experts,
is it possible to build an amp with one single output tube and more than 12 Watts?

All the Schematics i find with one EL34 or 6L6 speak of: "about 10 to 12Watts"

But If a PP amp with 2 6L6 puts out up to 50 Watts, shouldnt it be possible to build an SE amp with about 20 Watts?(I know that it has to do with the class A thing with SE amps, but do they always have to be in Class A?)
Or is it the OT that limits here?
(For example i have a OT with 5k/8 that would be correct for a 6L6 SE but is rated for 5/8 Watts)

Thanx for any comment or/and any schematics!

[Joe Bee]

Hi Rex,
short answer: No, its impossible. Single Ended HAS to run Class A, which is inherently more inefficient than Class AB.

The reason boils down to that the single valve always has to pass current (this is the definition of class A), sometimes more and sometimes less, and on average half of the maximum current. This is exactly where the dissipation is highest, with more current there will be less voltage across the valve so the P=V*I loss goes down, and with less current the same thing happens. This is what people refer to as "bias for maximum dissipation".

In Class AB on the other hand there is no (or very little) quiescent current, so only when you hit a string the current will reach the maximum dissipation point for an instant, but then go past so the dissipation in the valve will again be less. For this reason you can safely design the stage so the current goes way beyond the maximum average dissipation, for example with a a 6L6 you can safely have 50W instantaneous dissipation in a single valve. In fact with a pure Class B design, you can easily get 100W from a PAIR of EL34.


Regarding the original question
"is it possible to build an amp with one single output tube and more than 12 Watts?"
well it is, but not with a 6L6. If you look into radio transmitter tubes with graphite plates you can easily get 100W or more plate dissipation, and I think some audiophools actually use these tubes.

[MWJB]

Watts are normally based on an amp at nominal distortion, it's very likely an amp is actually making more power than the RMS rating in use, under full distortion. 20W? I don't know, SE is not as efficient power wise as PP - if it did make that much, would it necessarily be making a sound that was good to listen to?

Fixed bias, plenty of B+ and a SS rectifier would make your amp sound louder, you'd have to do some ear testing to arrive at a reasonable balance between tone & volume. The Carr Mercury runs 6L6/EL34/6550 in fixed bias and is rated at 10W, Kendrick Black Gold 5W runs a 5881 in fixed bias. This suggests that 20W from a single 6L6 may be a tall order.

The real limiting factor for your OT would be how much current it could take before burning up the primary.

[Steve Conner]

You could always try one of these, it's a 4-400A with 400W plate dissipation. I seem to remember London Power once made a single-ended amp with a blower-cooled 4CX250B too. Svetlana make nice triodes in the 4CX250B style finned ceramic package, and I've seen them used in audiophile amps.

[Satamax]

6L6, not possible imho but 6550! http://www.mif.pg.gda.pl/homepages/f...35/6/6550A.pdf

Bottom of page 2

[Joe Bee]

That's quite a pretty valve Steve, do you want to sell it? I was actually half expecting you to post a 811A from a Tesla Coil, but that one is a lot nicer!

[JJGross]

You could always try one of these, it's a 4-400A with 400W plate dissipation. I seem to remember London Power once made a single-ended amp with a blower-cooled 4CX250B too. Svetlana make nice triodes in the 4CX250B style finned ceramic package, and I've seen them used in audiophile amps.

That has got to be one of the coolest looking tubes I've ever seen.
Build a guitar amp with those under a screen cage and they'd sell like hotcakes. Who cares what it sounds like? "It looks SO COOL!"

Sort of begs for a reference to Buck Rodgers or maybe Frankenstein.

[rexindigo]

Thank You all, this is very helpful, as always in this forum and so Ill have to look for a KT88 /6550 Schem to start this next project.
id love to build a simple SE amp with a low parts count but with enough power to compete with drums.

[Satamax]

Hi Rex.

Well, there's a seller on ebay selling 3K 15W high end SE trany which would do good for a 6550 cheap enough. I think it's underrated. And may be you could push 20 watts at 5% THD through it. I was about to do this, but i'm always short of cash. http://cgi.ebay.com/Pair-3K-Audio-Ou...QQcmdZViewItem You'll have to go to the high voltage range around 400 or more volts. CF my first link.

Bye.

Max.

[Satamax]

If you want we make a deal. If you get the tranies cheap, we do a swap, i send you with 4 svetlana 6550 (real ones, winged C now normal or B series) and you send me one of the tranies. Does that sound good to you?

[rexindigo]

Hi Max, I also cant afford that much for this type of project.
But the link to the specs of the 6550 was very helpful and i will now start to gather parts for such a project. greetings Rex

[Satamax]

Hi Max, I also cant afford that much for this type of project.
But the link to the specs of the 6550 was very helpful and i will now start to gather parts for such a project. greetings Rex

Hey Rex, no prob But just to show there's hope http://cgi.ebay.com/ws/eBayISAPI.dll...m=280169698494 4 out of the last 5 auctions ended there, that must be his reserve price. Anyway, that's the way it gonna be with any brand of transformer. SE of moe than 10/15 watts is expensive!

[Steve Conner]

Hi all,

Yes, high power SE is always a problem. You may want to investigate the parafeed topology, which lets you use a push-pull O.T. along with a choke. The choke deals with the DC while the OT just transfers the signal. You could make the choke from several tube amp power supply chokes in series, to get the required high inductance.

JJGross, much as I'd like to make an amp with it, I'm not sure how I'd even start. A push-pull pair of those tubes would need a 2.5kV B+, put out nearly 1kW of clean audio power, and need serious fan cooling. The P.T. and O.T. would weigh about 40lbs each, and I'd have to make them myself, because my local audio transformer winders refuse to make things at those voltages for liability reasons. The amp would end up about the size of a small fridge, and need four 4x12"s to handle the output. :P

The O.T. would also have to be a miracle of engineering to get good bandwidth, with the required high ratio, and enough insulation for those 4-5kV peak signal voltages. In fact it might not even be possible to achieve all of these at once.

A single-ended circuit running off "only" 600-1000V might be more practical, especially seeing as I only have one tube... and I'm not selling it, Joe Bee :P

[Ampclutz]

Hi,

What about Weber's Lauren? 25 watts... SE....

AC

[rexindigo]

Hi Ampclutz,

do You have any link or even a schematic to "Weber's Lauren"?