Thanks everybody. Always good to have input. I tried switching tr's (like the BU508, and BUT11) before, Nigel, but the TIP family beat them (slightly) in total rise/fall. Power MOSFET's seemed like a good idea too, Hero, but the ones I played with before (like MTD6N20E) ended up slower than the TIP 48. The small signal ones are fast, but they don't fit my application. It's that inverse relationship Papa mentioned. I've also used SCR's before, like the old C231M, and newer ones, but they're slow, and they generate a lot of RF in my particular circuit. Microsemi used to make the GB201/GB301 series SCR's that were in the 200-400 volt range with Tr and Tq in the low nanosecond range; but they're discontinued according to their engineers. Same with the 3902GRF apparently. So I've settled on the TIP48 for now. I DID improve the trigger circuit a bit over the last 2 days, Nigel, with good results. I squared it up better, gave it a bit more amperage, and put in better pulse width adjustment.
Cheers, Bill