Its really not that hard to make one. I didnt have plans, but in Kamp's book on making turbines (and also in Shreckling's book) he discusses it briefly.

They tell you what KVA rated transformer to start with, and also what the secondary voltage range you should work to get.

I found a large transformer, cut off the secondary winding and rewound mine with 2 and a half turns of HEAVY wire (about 1/2" core) I got from the local industrial motor shop. It was trial and error for me, but after a few tries settled on the 2 1/2 turns.

I used a toggle clamp, and 3/4 square aluminum 6061-T6 for my arms, 1/2" diameter copper I turned into tips and have the whole thing mounted on a piece of wood. Momentary push button switch. I dont have a timer, but depending upon the thickness and number of layers you are welding you get to know how long to hold the switch down for...

If anyone is interested I can take a photo of mine and post it.

Andrew