Sedman Smythe

Hi I am looking for a bit of direction with a project . Some time ago I bought a Spark Eroder or EDM (Electrical Discharge Machine) Mechanically it is very sound, but the power supply is I think beyond economic repair. As I understand the power supply it works between 0 volts and 100 volts Square Wave with a variable output current from 10 to 50 Amps. Also both the off time and the on time are separately adjustable. I believe the original system used a lot of power transistors which were switched by push buttons to obtain the correct power setting. I am sure someone out there with a better understanding of modern electronics will have a good idea of how to achieve the supply I need to build. Thank for looking, any pointers would be very much appreciated. Jonathan Smythe