The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Tesla Impedance Coil a.k.a. "Tesla Hairpin Circuit" Tesla's original lecture setup.  For a detailed description of the lecture, click here. Large impedance coil - 56" tall x 40" wide - wound with 7/8" diameter copper. In the background is a 3 foot coil made of the same copper that might be useful in experiments with this loop later on... I have a few antique coils in the background too... For setting up this coil, I used a small 30 watt Tesla Coil power supply. It consisted of a tiny 3500V 8mA neon transformer, some doorknob caps - an adjustable array of caps variable from .001 - .015 mfd.  (I chose .015 for this experiment.) Then there is a standard 1920s 1/4" diameter tungsten spark gap with copper heat sinks. I also sat a 16" Pancake Coil next to the loop in hopes of showing some inductive effects. It doesn't have any electrical connection to any part of the circuit. My first test was with the Pancake Coil.  It was producing 3" sparks just sitting next to the loop. If I lowered the capacity, the sparks diminished.  With more capacity I might be able to get bigger sparks...?  The coil is wound with 21 gauge wire and insulated in wax and resin. Not the most impressive sparks but 3" isn't bad without any electrical connections! I tried to light an 11W mercury lamp and it lit to full brightness without any problem. I noticed though that my coil quit sparking when the lamp was lit.  It seemed to drain its power! Then I tried a 5 watt incandescent bulb.  It also lit brightly, but didn't drain it as bad. I still was getting a 1" brush discharge from the coil.