The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Inside Out Tesla Coil (Primary coil on the inside, secondary on the outside) Secondary was 360 turns of 26 AWG wound on 3.5" OD PVC Pipe Primary was 30 turns of rubber coated house wire, 12 AWG, wound on 1.25" bakelite pipe (2 layers) Coils were placed inside of a 6" length of 4.5" OD PVC and filled with wax. Tests were done with 30W.  .004 - .010 mfd.  3500V 8mA transformer. Here is a failed attempt at a small conical secondary coil.  Not all of my experiments work! 5 turns per layer, 31 AWG, spaced 1/16" apart every 5 turns.  Waste of time and wire, and with the last previous dozen attempts at conical coils...