..Chip ...Several years ago I ran into a fellow who said he had built a coil using a diathermy machine ... he said his secondary was 6 feet high and that he used a 1/2 turn primary! .. He said the rig would produce ball lightning!! .. not knowing alot about coiling at the time I took his word on it .. I also have never talked to him again ..but for what its worth, he said the diathermy machine worked very well ... Al Syme