The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Revisiting the half-size Tesla High Frequency Induction Coil Each Primary Coil contains 25 turns of 18 AWG cotton covered wire. Each Secondary Coil contains 120 turns of wire of 30 AWG Magnet Wire. Primary:Secondary Turns Ratio - 1:4.8 or 1:9.6, depending if the Primary Coils are wound in series or parallel. Note:  The secondary coils are Pancake Coils, however the discharge is taken from the outermost turns rather than the innermost turns.  It is interesting that both Tesla and Kinraide started out experimenting with this style coil, a natural progression from the standard Induction Coil. Testing at 600 watts - 5000V 120mA Cold Cathode Transformer. Condenser is only .004 mfd - Two 40kV .002 mfd Doorknob caps in parallel. This could easily be two Leyden Jars as well! Only 3 of the 16-series spark gap segments are used...gap can be seen in the back, which consists of 1/2" tungsten bar stock mounted between three 6" diameter aluminum fins with 1/2" shaft collars. Click here for a movie! Close to the discharge... Hot sparks extend 5 - 6" depending on the adjustment of the gap. If the gap is opened more, sparks pass from coil to coil.  Remember Tesla's Coil was under oil!  These are impregnated in toilet wax rings and linseed oil melted and cooled to a consistency of vaseline.  The coils are housed in cardboard shipping tubes with fiber end caps. Same coil powered by only a 4kV 30mA neon transformer. Rendering of simplified Tesla Induction Coil. Each primary is cylindrical, and each secondary is centered above in the form of a flat spiral.  In reality, the spiral is wound with paper interleaves and whole assembly boiled in wax and oil afterward for insulation.... Front view Top view Front view of coils (C) Jeff Behary, 2007, 2008