The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com  A Simple Design For A 4 - 6" Induction Coil Various simplified Induction Coils I built this week.  Front Left, 2.5" Spark Capacity Front Right, 1" Spark Capacity; Right, Vertical Coil (Heavy wire) 2" Capacity and the latest coil (rear) 4 - 6" Spark Capacity Setup.  Primary Winding is lead to far ends of cylinder, high voltage winding leads to the top of the cylinder, 12" apart. Secondary Coil is 2.375" x 14" containing 12" wound with 34 AWG wire.  4 turn primary coil of 2" wide copper ribbon on a 1.5" square x 13" long core. Click here for a movie!