The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Bipolar High Frequency Tesla Pancake Coil Many thanks to Steve for the Brass Bed Balls! General arrangement of Pancake Cols / Condensers / Spark Gap Operating with 9kV 120mA Cold Cathode Sign Transformer Coils, Front View.  9" Flat Spiral Coils, 26 AWG wire, 2 1/2 turns of 1" copper ribbon for Primary Coils Top View Capacitors are 40kV Door Knob Caps .002 mfd each Hot Discharge 4 - Series 1/8" diameter Tungsten Spark Gap...adjustable with shorting rod (Copper with Acetal handle)