Opening MOSFET's gate with low voltage PWM
Based on the information you've provided so far, the schematic posted below will allow you to build something that works and that you can play around with using the active stuff you have on hand. 

Since the LM393 is a dual comparator, you should spare out the unused one by connecting its  + and - inputs, and its output, to ground.

If you want to, you can also connect your LED in series with R5 to watch it blink, but make sure you don't connect it backwards or you'll destroy it.

Also, watch out for that 80 volts; it can give you a nasty little sting.