The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Pancake Tesla Coil Operated Directly From 220V! Ca. 1910 Frank S. Betz Pancake Tesla Coil in need of  some help. Top view.  6" OD. Bottom view - interleaves of paper between layers... Closeup of windings - 18 turns per layer Total secondary coil 1500 - 2500  turns or so...give or take a 1000? Still a Tesla Coil - 100%... Primary coil - Copper wire, looks like 10 AWG Sticky beeswax and rosin after hardening Oops.  Mejla! Repoured Betz Coil - Power supply is approx 100 watts.  110:220V transformer, reactance coil to limit the 220V, 1 mfd cap from a microwave oven (yes, 1 mfd - not .1 or .01 or .001!!!), precision tungsten spark gap adjustable from less than .0005" to .001" or so for these very low voltage experiments. The sparks are hot, as if from a Diathermy Machine - longer in length though (up to 3") yet just as hot. Hissing effects! Beautiful ribbon discharge to electrode A lot of current in the discharge for an apparatus consuming only 100 watts - 220V at 450mA or so... Unusual setup.  Tesla said he could maintain a spark gap with as little as 200 volts.  220V isn't bad! The actual voltage measured on the cap was around 234V. Don't want your finger near this one! Who says microwave oven caps are bad for Tesla Coils (well, normally it is true!)...