• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

output transformers

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I'm trying to find anything about designing and winding an output transformer.Calculations for core area,primary and secondary winding etc.If anyone knows something please I need to know.
Are there any books?I've heard somewhere about Menno van der Veen's book.But I can't find it!The title is "Transformers and Tubes".

There are some books in Old Colony Lab Sound about audio transformer design for tube amps.

A general book about transformers usually has informations too (number of turns, area, losses), but I think it's better see specific tube amp design transformer books, because there are much more information about construction details to improve the quality of the transformer.

I have one book about transformers wich covers audio transformers considering the general theory, but it's written in portuguese, if it's not a problem for you, I will be able to send you more information.

Thanks for the replies!
Elvis Rakic's calculations are ok.But are only for single ended amps.I'm interested for push pull and ultra linear amps.
I found an advertisment of Veen's book at Plitron's site and I think it's based on toroidal xformers.What about calculations for xformers with laminations?At Old Colony there's a book wrote by Flanagan.Does anyone know anything about it?
Blmn,I don't know portuguese but any information is acceptable!

I have the Flanagan's book (Handbook of Transformer design and applications) and I can say it is a little bit complex. It considers wideband performance for audio transformers and I think it won't be a problem if you have previuos math and electromagnetism skills, but it's not a pratical design handbook.

The brazilian book I have is "Transformadores" by Alfonso Martignoni - Editora Globo. It's old but it's still valuable. It has practical examples and a simplified way to determine the transformers caracteristics, but it does not consider the upper frequency behaviour of audio transformers or even the impedance models. If you wish I could scan the pages and send it to you, If you have brazilian or portuguese engineering students near you for shure they will help you on translating the text about EI audio and low power transformers (20 pages, but almost all are full of pictures and equations). I have done many designs for transistor output and driver transformers in the past using it and I didn't have problems.

About Plitron's book, I don't know the book but I can say there are many transformer parameters and carachteristics wich are valid from any shape of core, so it would be a good reference for you too.


Thanks for your interest
Maybe I'll buy Menno van der Veen's book.I think it'll be what I need.
But I would also like to see your portuguese information.
I think that from the pictures and the equations I'll understand a lot.I'm too interested for the EI audio text.
Haven't tried one, But when I found the sight and realized what he was doing, my first thought was What a loon.

Then I thought maybe the lack of barkhausen effect might be a good thing, its supposedly why AlNiCo is better is a magnetic material in speakers.

I can't imagine his getting a high pimary inductance, so is their any bass?

Listening is the final arbiter and he was brave enough to try a very unusual idea.

If anyone here dose get an amp going with one I hope they will report back

Have a look at: http://homepages.enterprise.net/icedragon/new/distribu.htm
good article on Types of Distributed Loading, at the bottom of the page under references
A Home-Made Output Transformer by W. Groome. from oct/nov 1962 Practical Wireless
424k zipped download

Regards James
It is a painstaking art to design and make a really good output transformer. If you never have built one, be prepared to a long course of tries and mistakes.
I suggest to read every book, but to filter it's content through the mesh of your basic background. The design of high quality wideband audio transformer requires really deep background in electrodynamics and materials science. Although it is relatively simple to calculate the core size and number of turns, it is just the beginning of the design.
To determine the exact geometry and winding configuration, one has to make some suggestions about the sectioning, wire layout, etc. Then you will be able to draw the actual winding scheme, and to calculate the parasitic parameters and, hence, the transfer function of your transformer with different loads. If your assumptions appeared to be far from optimal ones, you will never reach the goal. Therefore I suggest you first to analyse existingn designs of really good transformers in order to understand the logic of their designers. And then you may will be able to take some steps ahead.
Yes, it's very difficult to make a good output transformer.
I've built dozen of bad transformers before I have discovered "secrets" to make acceptable ones, and more and more before they becames good transformers. Another problem is reliability... isolation between windings is not simple, and appropriate materials difficult to buy in small quantities.

Regards, P.Lacombe
I have some experience on transformers but only for power supplies.Nowadays I built an output transformer and yes it's very difficult.I know a lot of 'secrets' on winding.But with this one I understood that I don't know nothing.I spent 8 hours to built it.Now I'm going for the second one.With better isolation and an other design between the changes on the primary and secondary layers.

I'd like some help on books.I can't find a lot of them.I bought Menno van der Veen's book but there's nothing to find the core size,the number on turns e.t.c.
What about Flanagan's book?
Regards George
Transformer design

The insulation strength is not a great problem for really high-quality output transformers. To obtain the greatest HF extension of bandwidth one has to lay down the turns in precise order. The turns are to be uniformly distributed over the winding surface, and the number of turns for each layer is precisely calculated. In this situation the insulation breakdown is unlikely to occur, because the insulation strength of common winding wires is above 500V DC. The precise insulation is to be inserted between each two adjacent layers is always required. If one uses high-quality insulating paper 0.1 - 0.2 mm thick, it will be enough to withstand everything. Also this paper forms an uniform substrate on which to lay down the turns.

Sorry, I saw no book (till now) where the design of wideband audio transformers is described correctly.

In overloading conditions, transients as high as 2~3 kV can be produced between one end of the primary and the secondary. The major difficulty is at the edge of each layer. Paper can be used for insulating purposes, but must be impregnated with adequate warnish, or the transformer must be sunken in paraffin oil.

Use of 0.2 mm paper between each layer of windings result in total thickness of insulation of several mm, this can be a problem. Mylar of 0.06 mm is best, but it's difficult to make correct windings without machine.

Regards, P.Lacombe
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