Steve,
Also, mosfets do matter, of the 1/2 dozen I have on hand they give me a range of 300v ptp to 700v ptp, except the irfbc40, which produces the 2.6kv, I've favored this mosfet for some time now, it is worth looking into the datasheet to see the difference it has, and nicely, they are cheap on ebay, about 50 cents each
kb