What defines LL on toroids? I mean, if I send a wire down the center of one, is it zero? Nothing can be zero...
If it were an air core toroid, then it would be the ratio of a few diameters, probably with a logarithm I'm guessing. And if it's a ferrite core with such and such permeability, then it's roughly that many times less leakage, right?
Additional question: can I calculate LL on, say, a dual C type core? What defines that? Ugly geometry-dependent math I'm guessing, but how about ballparks?
Reason I ask is, I tried this:(That's 6 turns 1/4" Cu tubing secondary, in series with 20uF and 1uH, and 24T 8AWG primary.) Resonant frequency was way low, like, lower than I can go, which was 15kHz. It's supposed to be 35k, so LL is at least 5 times bigger (>5uH). What was it actually at, and can I estimate it for a toroid?
I contemplated wrapping a slab of copper sheet around the core (to short out the leakage flux), but after a few minutes operation the primary winding was too melted to try anything more. On a related subject, I now despise proximity effect. ;-)