Half-wave rectifier circuits have been built up to voltages in the megavoltrange, in general by extending an existing h.v. testing transformer to a d.c.current supply. The largest unit has been presented by Prinz,5who used a 1.2- MV cascaded transformer and 60-mA selenium-type solid state rectifiers with an overall reverse voltage of 3.4MV for the circuit. The voltage distribution of this rectifier, which is about 12m in length, is controlled by sectionalized parallel capacitor units, which are small in capacitance value in comparison with the smoothing capacitor C (see Fig. 2.14). The size of such circuits, however, would be unnecessarily large for pure d.c. supplies.