The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com  A New Form Of Induction Coil I tried my hand at winding some more complex coils...and here is something simple. Secondary Coil is 2.375" in diameter x 12" long.  800T of 29 AWG Magnet Wire Primary Coil is Copper Ribbon, cut from Roof Flashing, .75" wide.  8 turns. Core is built up to 1.5" from 1.5" wide x 13" long. Sparks 1.5" long. A crude test to see how it works for high frequency work. Finished Coil EPDM rubber spacers to center the core. Pancake Coil