Abstract: A circuit arrangement for applying low frequency high voltage waveforms across a load and which includes low and high voltage circuits. The low voltage circuit includes a sinusoidal signal generator for producing a low voltage electrical waveform, and a transmitter circuit having first and second light emitting diode circuits by which first and second light signals are generated which are transmitted to the high voltage circuit by respective fibre optic light guides. The high voltage circuit includes first and second high voltage d.c. supplies and first and second triode valves.