[TCML] Toroid size

[Jim Calvin]

I have just finished a building a medium sized tesla coil.  It uses 9KVA @
120ma.  It has an 8" x 33" secondary and uses a dual tungsten spark gap with
a fan.  It has a primary tank capacitance of .0346uF made from an MMC cap.

 

I tried running it with my 30 inch toroid that I use on my big coil (7.8KVA,
7 feet tall).  I know this toroid is too big for this coil but it is the
only one I had available, besides my 12 inch toroid which I believe is too
small.  With no breakout point I got nothing.  When I put a breakout point I
got about 2 foot arcs.  Now I expect to get about double that with the right
size toroid.  So my question is: what is the proper size toroid for a coil
of this size and power? (18 inch, 20 inch . etc).