The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Low Voltage Pancake Coil - 240V 8.5 mfd! Hot crackling Sparks Setup.  120 - 240V transformer, current-limited with electromagnet to around 100 watts. 1 mfd MOT cap + 7.5 mfd Motor Start Cap = 8.5 mfd.  Micrometer 5/16" diameter Tungsten Spark Gap, set around .001". A normal Tesla Coil circuit with far from normal values. Closeup of Sparks