The Turn Of The Century Electrotherapy Museum

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