Winding output transformer

[SolderIron]

anybody has experience with winding your own output transformer?

First question is the transformer core the same material as power transformer? My guess is probably not.

 

[Rob]

Yes, sort of.

Some toroidal core power xfmers can be modified to make good output transformers, or used as-is successfully in the right circuit configuration. You need low plate impedance output tubes as a start, and you have to keep DC either out of the core as possible in a parafeed design, or cancelling as in a P-P design. Cathode coupling more normal Hi plate Z output tubes is a good possibility for using a standard toroidal power xfmer. Underrate the VA by at least 100% for every octave you wish to go below 60Hz as a minimum. 20-25% of the labelled VA is probably OK for 20 Hz.

The steel in high grade laminated E-I cores is better in good output transformers, and they use thinner laminations than in mains driven power transformers. Interleaving of windings is also necessary for a good product. There are so many things going on that it is a 'black art' as viewed fromoutside. Fun to play with but if you need guaranteed performance and cannot invest a lot of time just go buy one.

 

[SolderIron]

I have a transmitter with good size output tubes gethering dust. I am thinking about using the tubes and power supply for an audio amp. I have not think this through completely. It is rare to find output transformers nowadays and this is probably a higher than normal power unit.

Bob, It makes sense the output has thinner laminations to limit eddy current/ core lost. That is a question of efficiency. You think if there would be problem with frequency response if I keep in mind what you say about the low end frequency?

 

[Rob]

SI,

I've spent a lot of time thinking about just this sort of thing. What mode do you wish to run. i.e push-pull or single ended? What output tubes? Triode mode or other? What plate voltage is available? How many watts do you want or just settle with what you get? You gonna keep the grid drive simple and limit it to A1, AB1 or will you be able to source grid current and go A2 or AB2?

As for the output transformer lamination question, you are on your own here, but if you answer my questions I might be able to recommend a transformer.

 

[SolderIron]

Rob,
I have to go to storage to look up the tube. The rig was given to me a while back. I remember it has 2 good size power tubes much fatter than 6L6. If both of them works I will want push pull and class AB to get high power output. I will get back to you.

 

[Rob]

OK, let us know. If you want stereo you will have to support another set of two tubes and the power supply may not be capable of all that current unless you scale back on power. This may not be practical.