Improvements in trapatt pulse generators are described. By using two diodes in a push-pull configuration, pulses around 250 ps duration with up to 800 W peak power can be produced with repetition rates around 1 GHz. Measurements of diode breakdown under controlled high-speed voltage pulses from such a generator have been made on X-band trapatt diodes. These measurements show that relaxation-type oscillations can start in resistive circuits and thus support the relaxation oscillation theory for the starting mechanism of trapatt oscillations. They further suggest that high-frequency trapatt devices may have difficulty in operating efficiently at frequencies lower than some particular value determined by the relaxation oscillations.