We describe an electro-optical switch based on a commercial electro-optic modulator (modified for high-speed operation) and a 340 V pulser having a rise time of 2.2 ns (at 250 V). It can produce arbitrary pulse patterns with an average repetition rate beyond 20 MHz. It uses a grounded-grid triode driven by transmitting power transistors. We discuss variations that enable analog operation, use the step-recovery effect in bipolar transistors, or offer other combinations of output voltage, size, and cost.