I just built a power transformer for electrostatic headphone amplifier.
I had a scrap transformer broken, I kept it good the core and the plastic sprocket. I used very good copper with 2 layers of enamel, high temperature, used in electric motor, as insulator a special paper with mylar.
For convenience I used the free software available on the site of Fabrizio Giunchi, a very good tool for power and output transformers, even for custom Irons.
I have no coiler, so I made the winding by hand.
I tested only with no load, voltages are good, 2% of difference between hv secondaries, not a big trouble.
That's the link full of good info about transformer, it's in italian language