The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com  4" Capacity Induction Apparatus... ...Powering a Tesla Coil! 4" Induction Apparatus operating on its own. A series spark gap is now placed in parallel with the induction coil output, and a Tesla Coil with a condenser in series is then added. The Tesla / Oudin Coil is wound on a 2.375" OD form - 25 turns of 18 AWG wire and 750 turns of 34 AWG.  The secondary winding  is only 5" tall. Produces a discharge 4" or so in length. Though this induction coil will spark 4", when a condenser circuit it can only be used to charge smaller condenser - .002 mfd is used for these tests.