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Old 27th Aug 2019, 10:23 pm   #22
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Interstage Audio coupling transformer

If you measure the wire diameter (and the insulation thickness if there is insulation between layers) with a micrometer and then the cross section of the winding area and volume of the winding can be fairly closely determined from its shape, you can then calculate the number of turns of that wire that will fit in there. I have done this many times where a transformer with fine wire has gone O/C. If there is a DC resistance figure, from a schematic , it helps to check you have got it about right. (Try to estimate the cross sectional area and average length of a turn that the wire uses is the main task).

The thing is to acquire wire that is as close as possible to the original diameter, and put in in a cross sectional area that the original wire had to occupy. (you probably won't be using the insulation between layers).The average length of a turn will end up close enough.

For example, for some fixed sized winding cross sectional area, number of turns that will fit there is inversely proportional to the square of the radius of the wire and the resistance of the wire is inversely proportional to the square of the radius of the wire too. This means that the resistance you end up with is inversely proportional to the 4th power of the radius of the wire, so a small error in the wire diameter has a big effect on the resistance, and the inductance too which is proportional to the square of the number of turns you put there.

Or, you can unwind it and count the turns, that for very fine wire, can be time consuming and tricky.
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