I designed a laser controller in 2002, and it's licensed to a contract manufacturer. Parts are headed for end-of-life. Old Xilinx FPGA, 68K CPU, things like that.
It has a custom transformer in the isolated dc/dc converter.
The guy who designed it, long gone, was a former Signal Transformer employee and he went wild: litz wire, bifalar, the works. We can't get the header any more so I have to redesign it.
I hacked one onto the board. It uses #30 solid Beldsol (thermal strip) wire, which seems to be OK. No bifalar or any fancy winding tricks. At about 18 watts out, overall efficiency is 85%.
In theory, one should fill the available window area with copper, but this works about half full, with the #30 that I have handy. I suppose I could let the CM build it just like as shown, but maybe I'll make a small PC board with some sort of pins, to replace the surface-mount header.
What's neat about a pot core is that you can peek in through the gaps and see how hot the wire is running.
I drilled the board and added a 4-40 screw to hold everything together. Luckily the only thing I hit was ground plane. It doesn't look like the mag field induces significant current/loss in the stainless screw. Most of the field must be confined to the ferrite.