Paul,
I've noticed that if a static spark gap overheats, multiple racing sparks
may form at many places along the secondary. It's possible the
racing sparks were more concentrated at a certain area of the secondary,
but I don't really remember. I also don't remember if the racing sparks
began at a certain area then spread over a wider area as the gap
overheated
more. The overheated gap probably quenched very poorly and let the
oscillations continue longer than usual with more beating of frequencies.
I was surprised by the intensity and high number of racing sparks
under this condition however. I'm not sure if there's any relationship
to Brandon's coil's behavior, but I figured I'd mention this.
Cheers,
John