A simple and inexpensive method of stabilizing the output voltage of a mains driven doubler type high voltage generator is described. The stabilization system employs the closed loop principle and the regulator uses two silicon controlled rectifiers or thyristors. It has proved possible to set the output voltage of a 250 kv generator at any value between about 30 and 250 kv and maintain it constant to within ±0·10% in the presence of supply voltage changes amounting to ±10%.