Size Of Wire Used In Power & Output Transformers

[Pollys13a]

Hi,
What size or sizes of wire would be used in making power and output transformers?
Thanks.

[Stevem]

I say this with all due respect in advance, if you need to ask then don’t try making one of either until you have got your hands on a few dead ones of each and unwound them.

[roberto]

What stevem said.
You should find a thread I opened years ago (a decade?) with specifications of most Marshall output transformers.

[Phil_S]

I say this with all due respect in advance, if you need to ask then don’t try making one of either until you have got your hands on a few dead ones of each and unwound them.

FWIW, I also second this recommendation. There is a great deal to be learned from unwinding a transformer. I couldn't believe how deceptively simple it is to wind a power transformer and how complicated an output transformer looked to me. For example, though it was obvious from doing the math, at first I didn't believe that a secondary 6.3V filament winding had only 19 turns and the wire was really fat! If you don't have any to tear down, you can buy them cheap on ebay.

[thetragichero]

"how long is a piece of string?"

[R.G.]

What size or sizes of wire would be used in making power and output transformers?

I will add my voice to the chorus: the question by its nature indicates that you need to learn a lot more about transformers, and maybe electrical circuits in general before messing with making a transformer. There is a lot of underlying stuff that gets you to the answer. Wire gauges inside PTs and OTs vary hugely.

The basis of the real answer is that the wire should be big enough so the current flowing through it does not heat the wire enough to melt its insulation and cause a short in the winding. That varies, of course, on what the temperature rating of the insulation is. Some common insulations are only good to a wire temp of 105C, some to 130C, some higher. So first of all, it depends on the current in the winding and what the temperature rating of the insulation happens to be.

You, the transformer winder, generally want to buy the least amount of expensive copper that you have to, so you want to use the smallest wire you can and still not have it overheat. A really good goal in transformer design is to not have any hot spots, places that get hotter than the other places in the winding. This in turn means that you want equal self heating from currents in all the wires; and that in turn means that you want to make the power per unit of wire length (which is equal to the rms current in the wire, squared, times the wire resistance per unit length) be equal(ish) for all the windings. The current-squared part of heating means you may have to adjust the wire sizes a lot to get about equal heating.

And transformers work better if you impregnate the windings with something - varnish is most common, beeswax was used too - to replace the air inside, as almost anything you soak inside the windings will help get heat out better than insulating air. Impregnation means you can get more heat out, or for the same heating use smaller wires or a smaller core.

It's almost solid variables, very few "just use this...".