Winding output transformers

[M Gregg]

Hi,

First post!

Is it possible to wind an output transformer for a KT66 valve in single ended?
I have built valve amps before, however I would like to try winding an output transformer. Would a ferrite ring work as a core?
Can any one tell me number of turns and possible size of core.

Regards
M.Gregg

[Miles Prower]

Originally Posted by M Gregg

Is it possible to wind an output transformer for a KT66 valve in single ended?

Yes.

I have built valve amps before, however I would like to try winding an output transformer. Would a ferrite ring work as a core?

No. There are a couple of major problems with that. If it's an OPT for a single-ended final, the DC bias current will saturate the core, unless there is an air gap. Unless you have a gapped toroidal core already, you're gonna have a helluva time trying to cut a ferrite core without breaking it.

Secondly, ferrite won't give decent low frequency performance since its perm and Bsat are a good deal lower than that of a proper silicon steel core, or one that uses more exotic materials, either alone or in combination with Si-steel lams.

Save your ferrite toroids for RF projects.

Can any one tell me number of turns and possible size of core.

Wolpert Audio Transformer Design Manual: it looks like this is no longer available over the 'Net. Send me an e-mail, and I can send it back as an attachment.

Keep in mind that OPT design and winding is somewhat of a "black art", and requires empirical design gained mainly through experience. You might have to wind more than a few bad/mediocre OPTs before you get that experience.

Winding bad audio xfmrs is easy. The good ones take some considerable doing, which is why the really good ones are $Pricey ( and why cheap ones sound like: )

[Yvesm]

Wolpert paper is here:
http://www.dissident-audio.com/AutoI...ign_Manual.pdf

Yves.

[Zen Mod]

Originally Posted by Yvesm

......
Yves.

one of Black Art Gurus

[Matt.B.H.]

M Gregg,

I like your idea clearly ferrite is no good, as stated by Miles.

Send me a PM and you can have a pair of M6 c-cores for postage.

I recently scored a whole load of c-core trannys and the cores I had are no longer needed. They are some of the core kit jobs sold on ebay from China. I tested them at 50Hz and for the pair they can handle 300VA, so for one core in single ended with a (or pair of) KT66 etc. they would be ideal.

I have been messing about winding some push pull trannys so you will have to do a lot of reading, winding, wondering, re-reading, winding again etc. but the cores should be a start

The whole subject of winding your own outputs has been neglected slightly on the forums. Possibly because it is hard work, both in maths and the actual winding. After all this the final design is likely to be flawed and a re-jig/re-wind is needed

I dont mean to disuade you in any way because its the most fun I have had in a while just getting the bits together ie ECW, insulation, making bobbins, finding cores.... the list goes on.

The best info I have found is the bible:

http://www.pmillett.com/tubebooks/Books/intro_RDH4.pdf

and Patrick Turners great workdown:

se-output-trans-calc

( If you want the cores, be sure to PM me before Monday morning as I work away four days a week and may not have internet access)

Cheers Matt.

[LAZAROIU]

Originally Posted by M Gregg

Hi,

First post!

Is it possible to wind an output transformer for a KT66 valve in single ended?
I have built valve amps before, however I would like to try winding an output transformer. Would a ferrite ring work as a core?
Can any one tell me number of turns and possible size of core.

Regards
M.Gregg

Hello!
Can design and build an output transformer for a SE KT66 tube, but first you must determine what diagram you use, the performance you want to get this project (!?).
Audio applications, can not use a ferrite core, only E + I, C core or toroidal.
If we see a diagram that you use, I think I can help with this project.

Nice weekend!

O.Lazaroiu

[BudP]

A KT 66 will work fine in SE mode. With 440 VDC on the plates you can expect to get 5.8 watts. Is this enough power for your needs? It will certainly drive a Lowther of any kind to quite loud levels, but anything under 90 db sensitivity will be starved for dynamics.

If you are serious about learning how to design and build an OPT I can help you move down that road. Designing audio transformers is part of my professional life and I will be glad to help you.

This is not something that can be learned quickly, though it is not particularly complex. It isn't a Black Art either, I don't have to wear a flowing caps with arcane signs stitched on to it nor a pointed cap. Just a few simple formulas, some hard to obtain technical data, and you can design very good transformers, for commercially available materials.

Learning how to make the things, that is a bit more involved, but again, a few simple rules applied in the design portion will help this part tremendously.

So, how serious are you?

Bud

[Soonerorlater]

The whole subject of winding your own outputs has been neglected slightly on the forums.

Agree with Matt here. Winding output transformers must be the "holy grail" for amp builders. I would be happy on my first attempt with one that simply worked, anything else would be a bonus

[Zen Mod]

Originally Posted by BudP

....

So, how serious are you?

Bud

.... BudP ...... certainly one of Black Art artisans

best thing can be - if you are willing to make short ( not so short - not short at all ) thread or blog - with that theme ......

I presume that only already knowledgeable members will contribute , not making noise in so precious theme

I never take my self as complete tube DIY-er , just because I never had enough time to invest in necessary time consuming process of learning little tricks in OPTs calculating and making .

making stage with xformers made by someone else just never looks complete enough to me , so I never said that I made some amp by my self completely

[Soonerorlater]

There are many popular schematics on this forum using EL84's in push pull topology. A blog/ thread leading us less capable down the road to an OT of about 15w, Raa of around 8k into 8ohm would be fantastic. It would certainly keep me quiet