The Gamble I pulsed electron beam generator at NRL recently has undergone several major modifications. The modified generator has a nominal output into a matched 1.5-Ω load of 500 kA at 750 keV, with an 70-nsec (FWHM) pulse length and a 20-nsec (10%–90%) voltage risetime. The distinguishing characteristics of low prepulse (< 1%) and high reproducibility in output voltage and current (± 3%) result primarily from conversion from operation with self-breakdown water switches to operation with triggered high-pressure gas switches. Fast pulse risetime was maintained by using a low-inductance multichannel triggered output switch in conjunction with a new low-inductance vacuum diode with a radial insulator.