I am attempting to build a NE555 timer controlled step up transformer (3:250). R2 and R3 will be variable resistors when it is completed. Input is 12V and I'm stepping that up to about 1000V. The image shows the voltage across L1. I'm not sure why spice is showing a declining voltage wave. Is it the "ringing" of L1? In any case I need a 12V pulse. Any help would be appreciated.