The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Turpentine / Poulsen Spark Gap Powered Tesla Coil: Details The interesting thing about this gap is that it works.  The transformer used for this bipolar Pancake system is only 1500V Approx. Actual size - 1 second exposure Approx. Actual Size - 1 second exposure Click here for movie! S.G. Original Tungsten Spark Gap for these demonstrations is opened fully and our demonstration Poulsen Gap is placed in parallel replacing it temporarily. (Frank's nicely drawn schematic with a few minor notes added)