Amp Design - Single Ended Output Power..

[diddymix]

Hi guys,

After learning abit about amp design and tweaking an old one of mine I've decided I would like to try building an simple amp from scratch, and not just because they are a little simpler but I love the tone of single ended amps, especially the tweed style types from the 50's..
However I would like to get as much power as possible and would ideally like a clean amp with a fair bit of headroom, for more flatpicking and 'acoustic' styles of playing.. Could anybody give me advice on an output tube that can put out a lot of power in single ended??.. whether pentode or triode.. Is it possible to get as much as 50W with one output tube in SE?

I'm not so clued up on tube types and their limits, but if theres any pointers on where to have a look I would appreciate your guidance. I'm guessing also I would need to find an output transformer that would work with said tube..

Thanks

[TUBEDUDE]

For that kind of power you will need to use several tubes in parallel, with a huge output transformer. Like 4 kt-88 tubes and a 12 pound OT.

[Stevem]

Yes you can get like 20 watts RMS of single ended power out of one tube like a KT120 or 30 watts with two KT120 tubes or two more common 6550 output tubes in parallel, but the needed 30 watt single ended output transformer will cost you 152 bucks!

A 15 watt RMS SE amp is far cheaper to build my friend!

Don't kid yourself, 15 watts of clean RMS power is loud thru even just one good efficient 12" driver, but hey it's your wallet so open it up as far as you like!

If you build one for any power output level above 10 watts please note that as compared to a push pull output stage the single ended amp will need one extra stage of filtering ( first stage) to make up for the power supply hum rejection that a single ended amp does not have .

[Colossal]

No reason not to do this, if the single ended sound is what you are going for. As stated, running multiple tubes in parallel single ended will increase output power at an increase in cost for more iron in the output transformer. Look up Bob Gjika. He has some videos and maybe still a website for his Powers of 10 Shawn Lane amp. It is a 4xEL34 single ended amp. The transformers are quite large. Pretty crazy sound though. Very loud and very pure and rich. Others here, like Dartanion (Darin), used to build a 2xEL34 single ended Liverpool variant. Heyboer makes a very nice 30W SE output transformer too. I also had them wind a three primary tap SE OT for me a long time ago. You could swap in any octal you wanted and run them on most any tap, within reason. Adjustable cathode bias. It was a fun amp and sounded amazing through an oversized 1x12 with an EV. I tried loads of output tubes and for my taste, a KT66 running at 360V into 6k was really great. Fat and juicy and warm. Also, as Steve said above, you will definitely want to beef up the filtration. I would recommend a CLC after your rectifier. This will knock the supply ripple down far more than a CRC and you will appreciate this for your acoustic playing. The inductor will need to be rated for the full current of the amp. So the more output tubes in parallel, the larger that choke. I have a choke for a CLC power supply for a bass amp that is bigger than a 50W Plexi OT alone. It is rated for 500mA. Yes, this will result in increased cost but life is short and tone is fleeting. Who cares if the amp gets 5 miles to the gallon? Now that said, I am not into raspy, blocking distorted Champs running at the wrong voltages. I would also recommend adjustable cathode bias or even fixed bias. You may find, as I did, running them at 90-100% of dissipation is not the best sound. Run the load lines and have fun.

I have iron for a 4xEL84 SE and a 2x6V6 SE....need to finish up a couple of projects...

[Stevem]

The disapation to tone relationship is a big factor,that's why I posted about under using the KT120 output tube for a build of 30 watts.

[Colossal]

The disapation to tone relationship is a big factor,that's why I posted about under using the KT120 output tube for a build of 30 watts.

Very true! Big difference in sound and for the better, IME.

Edit: Diddymix and all, I did not mean to seem flippant about inefficiency in design. SE has an increased cost for sure, especially for parallel designs where current goes up significantly and with it, the cost of the transformers. A 4xEL34 or KT88 SE design would be AWESOME but it would expensive and heavy. But we do what we must!

[diddymix]

Hi guys. Thank you all so much this is really useful info.. Aghh. In this case then it seems i might just do a single that can do 15-20W.. maybe the KT120, and pair with an efficient speaker. I need to get more clued up on the hum rejection thing because ive only worked on a pushpull amp with PI. Thanks everyone! Anymore suggestions please do chime in, I'm guessing with a lower powered amp I could buy some clean headroom with negative feedback applied well..?

[sluckey]

There are some guys over on Hoffman's forum that have a lot of high power SE experience. May want to drop by.

[pdf64]

Checkout the Laney Lionheart series, even included a now discontinued 50W 5xEL34 model! https://www.headstockdistribution.com/b ... onheart/71

[statorvane]

The best amp I have built is a parallel SE amp using two 15W SE output transformers. It drives two 6CA7s for about 25 watts. Uses a Hiwatt DR103 preamp design. Not necessarily a clean amp with a lot of headroom; more of a rocker - real fun to play.

https://s165.photobucket.com/user/JKCav ... 103?page=1

There is also a large SE amp design by R.J. a forum member here, the Eagle Supre. I never built it, but it generated a lot of interest a while back.

[Colossal]

The best amp I have built is a parallel SE amp using two 15W SE output transformers. It drives two 6CA7s for about 25 watts. Uses a Hiwatt DR103 preamp design. Not necessarily a clean amp with a lot of headroom; more of a rocker - real fun to play.

https://s165.photobucket.com/user/JKCav ... 103?page=1

There is also a large SE amp design by R.J. a forum member here, the Eagle Supre. I never built it, but it generated a lot of interest a while back.

I remember that amp, Statorvane. Didn't you go by Pressed Rat long time ago? That was in interesting build and cool idea doubling up on the OTs for twice the fun.

The Eagle Supre was a fun project and some good ones were turned out. Although I would add a CLC at B+0 and feed the whole amp with it. I should look up my notes on the VAC ripple reduction before and after the CLC filter; it is quite significant and well worth the cost and effort of the choke. I remember using a 70R 10H 250mA choke.

[Colossal]

Checkout the Laney Lionheart series, even included a now discontinued 50W 5xEL34 model! https://www.headstockdistribution.com/b ... onheart/71

I didn't know they made that one, Pete. I was familiar with the 4xEL84 SE 20W model. Thanks for posting that.

[martin manning]

Link to the Eagle Supre: https://ampgarage.com/forum/viewtopic.php?f=6&t=14349

[tubeswell]

Figure a (very) rough guide where output power will be about 0.4X the rated plate dissipation of the output tube. So for a 50W output, you'll need 125W worth of plate dissipation. (And then there's all the other stuff - optimum load vs peak Ig2, amount of driving signal at the output tube grid vs output tube gm, OT saturation, speaker efficiency...) What sort of sound will you get? Only time will tell...

Edit:

Here's a candidate output tetrode http://rtellason.com/tubedata/4-125A.pdf - needs forced air cooling. Could be run in Class A but you need 2.5kV B+ and 20k3 reflected load to get to 125W Pmax. You'd want a really good insulation rating on your MM probe and a Big Ass OT and PT. It has been done https://www.youtube.com/watch?v=dTmUqEaURdA.

[statorvane]

Didn't you go by Pressed Rat long time ago?

Still do, over on SEWatt.

And if the OP is really sold on an SE design, that site is an excellent resource. Several long running projects / variations of a "Jones' Octal One", an all octal SE amplifier.