# Thread: 6L6 SE Amp with 20 Watts?

1. ## 6L6 SE Amp with 20 Watts?

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!

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2. 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.

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3. 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.

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4. 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.

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5. 6L6, not possible imho but 6550! http://www.mif.pg.gda.pl/homepages/f...35/6/6550A.pdf

Bottom of page 2

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6. 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!

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7. Originally Posted by 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.
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.

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8. 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.

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9. 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.

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10. 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?

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11. 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

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12. Originally Posted by 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

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!

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13. 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

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14. Hi,

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

AC

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15. Hi Ampclutz,

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

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16. Rex, for the sake of practicallity I would suggest you parallel a couple of lower power valves. Last time I checked the 6550 only had 40W plate dissipation so you will be hard pressed to get much more than 10W single ended output from one.

Steve, you need to think MOTs. They come free, pack a lot of power and the best thing is you can easily rewind them yourself since you can have a lot of volts per turn and don't need to mess with hair-thin wire. Don't tell me that after building 100kV+ Tesla Coils you are scared of insulating a transformer for 10kV or so. OK, make sure the amp never oscillates in the 10s of kHz region or you might have serious corona problems, but how COOL would THAT look in a guitar amp? :-)
Oh and I am sure that a single 4x12" could handle the power, just install a fan in the back and load it with EV 300W speakers, you know, this "the only speaker zakk wylde uses" one.

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17. Hi, in the meantime I found this:
http://www.ax84.com/static/corepower..._Schematic.pdf

which seems to be exactly what im looking for.

But to be honest, the thought behind my initial Post was, I have this really nice sounding EL84 SE Amp build: the Preamp i designed (guessed?) myself the Poweramp is borrowed from the P1 and the only prob with it is , i would love to have this thing a lot louder before it brakes up.

So how about two el84 in parallel, why not!

How do i calculate the parts for it? how does the specs of the OT have to be?

Or is maybe the parafeed technology the right thing, at least the OT would be at an reasonable price.

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18. Rex,

Here's a link to Weber's kit page... Schematic and layout available there. Or even the whole kit!

https://taweber.powweb.com/store/kits.htm

AC

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19. Why not use..... Two SE EL84 OTs in parallel!

Joe Bee, an audio amp made out of microwave oven transformers, hmmmm... The flip side of the volts-per-turn thing is that they leak stray flux and lots of audible hum and vibration. But I guess the wall of Zakk Wylde speakers would easily drown it out. :P

Seriously though, I might nearly have enough parts to rig up a parafeed single-ended setup with that 4-400A. I just need a large choke, and I think some guy on the TCBOUK mailing list has one from a radar power supply.

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20. Originally Posted by 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.
Does that actual say 4-400 on it?
I have a few of them and they don't look like that.
Mine look like this:

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21. Looks like with a litle missmatch Weber WSE25 trany could be used for SE6550, thought 40 dols, while the other pair goes for 90 usualy, which means 45 dols, i'd try a higher end one at 45

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22. Does anybody here remember the very lengthy and often contentious thread several years back concerning the THD Univalve and how much wattage it could really produce?

Of course the irony is that differences between 10W and 15W or even between 10 and 20W are likely to not be that audible given the usual relationship between wattage and perceived changes in loudness.

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23. Originally Posted by Mark Hammer
Does anybody here remember the very lengthy and often contentious thread several years back concerning the THD Univalve and how much wattage it could really produce?

Of course the irony is that differences between 10W and 15W or even between 10 and 20W are likely to not be that audible given the usual relationship between wattage and perceived changes in loudness.
Can't realy, but you might be able to find it?

http://archive.ampage.org/

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24. well 45\$ is not so expensive, but to be honest i never bought anything via ebay outside germany, so i dont know what shipping etc would cost and how long You would wait ?
Max, You live in France: did You ever bid in the US, what are taxes etc?

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25. Originally Posted by rexindigo
well 45\$ is not so expensive, but to be honest i never bought anything via ebay outside germany, so i dont know what shipping etc would cost and how long You would wait ?
Max, You live in France: did You ever bid in the US, what are taxes etc?

Hi Rexdingo.

Well, i just bought a nailer there. Two other ones in spring, a transformer etc. If you keep the price under 100 euros, you don't get caught for taxes usualy. Or you ask the seller to state it as "no declared value". Shipping wise, under 20 pounds, USPS Priority mail flate rate box is the cheapest at 37 dols.

Usps is usualy the cheapest. But if you're in germany, DHL is verry good too. I was saying 45 dols each trany plus shipping. I 'm bit short on cash and don't want to offer to do a group buy between us right now, but may be a bit later. Let me sleep on this.

Bye.

Max.

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26. ...maximum theoretical efficiency for Class A is 50%, but practical efficiency is only about 25-30% for beam tetrodes and pentodes (triodes are less).

...however, "parallel" SE Class-A (visualize 'one-side' of 4 x 6L6 push-pull Twin, etc.) would achieve 2 x 30% of 30W or about 18W with two 6L6GC's.

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27. Originally Posted by Old Tele man
...maximum theoretical efficiency for Class A is 50%, but practical efficiency is only about 25-30% for beam tetrodes and pentodes (triodes are less).
Hi Old tele man.

Thta's non distorted efficiency, or only with acceptable distortion? Not guitar levels? Or that's definite physical limit and the other 70-75% are heat and other byproducts losses?

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28. HI satamax,
yesterday i said to myself: "stop posting, start soldering" and added a octal socket to my SE EL84 Amp parallel to the EL84. (like in the very first P1 of ax84)
and although i cold not test it in the middle off the night it seemed to be a lot louder with the 6L6. i will try it in rehersal on friday, maybe i dont have even to buy hardware to achieve my goal.....

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29. IIRC, the maximum theoretical undistorted efficiency for SE Class-A is 12.5%.

Bruce, it doesn't have any markings, and it also has a graphite plate. I think it might be a 4-400C, and maybe Amperex or one of the Eastern European brands. I bought it from a guy who pulled it out of an induction furnace that he was scrapping.

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30. Somebody might want to try building an amp with this tube
http://cgi.ebay.com/ws/eBayISAPI.dll...m=270191489314
it's a GU-81, a Russian 750W pentode, so even with 12,5% efficiency you would get plenty of output.

It would definitely be worth using a push pull output transformer for this with a constant current source attached to the other tap. A gapped transformer with this power rating would probably weight a ton.

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

It's not Po=25W, it just uses a 25W OT for full frequency response. That amp would run somewhere in the neighborhood of 8-10W @ ~10%THD. The overspec'd OT gives about the same effect as running a Hammond 125D.

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33. Originally Posted by Ampclutz
Hi,

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

AC
Why not a Hammond 125 GSE ?

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34. satamax,
this is incredible, this must make a SE amp with at least about 50 Watt?
But a quick check in the Internet said: it costs about 100Euro and OT and PT will be expensive too. this might be out of my finance range in the moment

I changed my SE amp to an 6L6 output stage but i dont like the sound yet( i miss the sparkle) , it seemes to be louder than the el84 output stage ( though its the same OT) and worked in rehearsal quite good. i will have to tune it, but maybe its the character of the EL84 that i like and then i wont get it with an other tube, then i may have to go into the direction of el84 Parallel output stage, have you ever done such a thing? ( i only did it with 12ax7 in the preamp of my SE amp)

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35. Originally Posted by rexindigo
satamax,
this is incredible, this must make a SE amp with at least about 50 Watt?
But a quick check in the Internet said: it costs about 100Euro and OT and PT will be expensive too. this might be out of my finance range in the moment

I changed my SE amp to an 6L6 output stage but i dont like the sound yet( i miss the sparkle) , it seemes to be louder than the el84 output stage ( though its the same OT) and worked in rehearsal quite good. i will have to tune it, but maybe its the character of the EL84 that i like and then i wont get it with an other tube, then i may have to go into the direction of el84 Parallel output stage, have you ever done such a thing? ( i only did it with 12ax7 in the preamp of my SE amp)
Hi Rexdingo.

Well, sorry, but i'm no guru or master or anything. Just a guitarmaker who had to turn into an amp modder. I've destroyed the first three amps i've touched. And i've repaired several since. Two hiwatts. An eko duke an Ac 30 A SC120. A SC 100. Two BF bassman a super reverb and a bandmaster. An original JMP also and a JTM60. Plus i've had of mine 1 Fender champ 25SE, a JTM60, a Boogie mark2B, 3 sound city L120 2 L100 4 PA50, two of which have been transformed into guitar amps. 1 hiwatt circuit and one into a MK3 50W (which never existed!) But since i've hung around ampage from 2000 or thereabouts. I've learnt a great deal. Actualy, most of what i know about amps, and i've gathered many usefull infos. Most certainly, this big tube has been showed to me by Ken Gilbert, while talking about the BAGA. http://ken-gilbert.com/tubestuff.html. And for parallel SE, the two ever SE tranies i've had whent to the dumpster along with my first sound city 120 when my grand ma decided to clean the house while i was at school in UK in 96. Never had spare cash to get another one since.

Here's my best mod soo far. http://satamax.free.fr/mark3/
http://satamax.free.fr/newlogo.jpg http://satamax.free.fr/frontgluing.jpg http://satamax.free.fr/frontback.jpg http://satamax.free.fr/frontfront.jpg http://satamax.free.fr/faceplate.jpg http://satamax.free.fr/back.jpg http://satamax.free.fr/back.jpg

Started like this http://satamax.free.fr/pa%20edit%205.jpg

Sorry i can't be of any more help.

Bye.

Max.

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