Fun and games with pulse transformer

Well well well (my cat fell down a well, puss puss puss puss kitty kitty kitty, my cat fell down a well)
I tried another old CFL toroid, a little bit thicker than the first one, would you believe it works perfectly! So I'll use that instead of my newly re-wound transformer since it's 1/6th the size. Maybe even try another of the smaller ones. Curiosity has really got the better of me now (that was the cat's problem too)
(Sorry for the Man Tran outburst. I can't help it. Every time I say "well" 3 times)

All down to the ferrite used.
The one you used that worked is most likely power ferrite, isnt lossy at the frequency your using, and can withstand a reasonable flux density, ie able to store enough energy per cycle.
The test jig I referred too can tell you the flux density at saturation, and can give you an idea of losses at a certain frequency.