The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com 2008 Coils:  Some old concepts with new twists Tesla / Oudin Secondary Coil with variable pitch threads. Coil is 140 turns of 30 SSC wire, spaced from 14 to 4 TPI over 14" in length of 4.5" OD PVC.   Mejla guarding the latest coil forms: Inspired by Thomas Stanley Curtis Close-wound coil vs. space-wound coil. (C) Jeff Behary, 2007, 2008