Re: Help: How to wind a toroidal output transformer for push-pull applications?

[Denis]

(Steve Kendall) wrote in message >...
> I am planning to DIY output transformers for my future push pull power
> amplifier. After a few days search on the net, I can only find one
> place to sell EI laminations and another one to sell toroidal core in
> small quantity. Since the company selling EI laminations only offers
> EI-112 and the price is high, so I decide to stick to toroidal core.
>
> My first question is: can I use a toroidal core made by grain oriented
> silicon steel to make a good PP output transformer?
>

Certainly NO!


There are three reasons:

1. It is extremely difficult to maintain required precision of turns
layout.

2. The wideband OPTs benefit from increased iron cross-section, this
is difficult with toroids.

3. A very small, but finite airgap is essential for any PP output
transformer. The natural gap of, say, 25um, which is present in a
double-C core is just what doctor has prescribed, the IE cores are
similar, the toroids are not.

There are also reasons for being sceptical about Plitron OPTs.

Best regards,

Denis N. Afanassyev

[Patrick Turner]

Denis wrote:

> (Steve Kendall) wrote in message >...
> > I am planning to DIY output transformers for my future push pull power
> > amplifier. After a few days search on the net, I can only find one
> > place to sell EI laminations and another one to sell toroidal core in
> > small quantity. Since the company selling EI laminations only offers
> > EI-112 and the price is high, so I decide to stick to toroidal core.
> >
> > My first question is: can I use a toroidal core made by grain oriented
> > silicon steel to make a good PP output transformer?
> >
>
> Certainly NO!

Ask Plitron, and see what they think!

>
>
> There are three reasons:
>
> 1. It is extremely difficult to maintain required precision of turns
> layout.

See above.
But, for the diy person, toroids are hard to get right.

>
>
> 2. The wideband OPTs benefit from increased iron cross-section, this
> is difficult with toroids.

No, just use a large cross section of iron, and a large doughnut size.
But, difficult for the diyer, and E&I or Ccores are easier.

>
>
> 3. A very small, but finite airgap is essential for any PP output
> transformer.

Plitron don't have one in all their trannies.
E&I or Ccores have the effect of an air gap because of the
reverse direction of grain in the E&I lams, or the cuts in a C-core.
It is not mandatory to have a gap in every PP core, and it depends on design.
Some amps need a gap, and some don't.


> The natural gap of, say, 25um, which is present in a
> double-C core is just what doctor has prescribed, the IE cores are
> similar, the toroids are not.

Toroids can be supplied with a gap,
or Unicores from AEM in Sth Aust can also be supplied with a gap.
The latter can have almost an uncut core, but can be used with plain bobbin winding.

>
> There are also reasons for being sceptical about Plitron OPTs.

Indeed, but it depends which one of the many types one chooses,
and how you use them, or if you ask them to custom wind something.
Probably it costs a lot, but they do seem to be surviving as a company.

>
> Best regards,
>
> Denis N. Afanassyev

My old sparring mate.

Have a great weekend,

Patrick Turner.