Abstract: A power supply for a travelling-wave tube (TWT) includes a beam power supply (14) connected to the cathode and collector of the TWT, and a further power supply (20) connected to ground and to the collector for establishing the cathode-to-body voltage. A feedback cathode voltage regulator includes a transresistance arrangement (31) connected between ground and a terminal of the further power supply which, in one version, includes a cascade of a control transresistance device (32) with a plurality of further transresistance devices (234s) for reducing the voltage to which the control device is subjected. In another version, a plurality of such transresistance arrangements (A,B) are paralleled for reducing the power which any one device must handle. In a preferred embodiment, a current equalizer (240) equalizes the load carried by each of the transresistance arrangements (A,B).