SSTC probs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Fucian-at-aol-dot-com>

Hi guys, this is for the SSTC experts.Ive been using a simple 555 timer and 
IRF740 MOSFET to run a true tesla coil secondary.I get pretty good output for 
the fact its way out of tune.My input power is a 4.5amp variac.When I try to 
go abouve maybe 70 volts, the MOSFET makes a small little pop noise and 
output goes to zip...WHY?Ive killed maybe 10 now!Whats happening?Ive got a 
150amp 1200volt hyperfast diode on the output to the coil.Anode towards the 
MOSFET and cathode to the coil.I also have another identical diode going 
across the source and drain.They both get a little warm.The MOSFET is on a 
fan cooled heatsink.It gets really hot.

Matt