A relatively simple high-voltage (HV) buck regulator circuit using a series crossatron switch tube is presented. Implementation of the buck regulator circuit led to a HV sensor investigation. This investigation resulted in a novel high-voltage sensor circuit using a FET as a constant current source. The novel sensing and logic circuit samples the pulse discharge capacitor voltage and generates turn on/turn off triggers to the series crossatron switch tube to control the recharge time of the pulse discharge capacitor. Circuit analysis by Fortran programming and P-slice analysis indicate that the buck regulator design goal of 0.02% HV regulation can be met under the worst conditions of line and load variations and high PRF (pulse repetition frequency) stagger ratios. >