Abstract: There is disclosed a self-protective system for administering an electrical shock to a would-be assailant by first establishing a low resistance path to the nervous system of the assailant and then coupling thereto an interference signal voltage having a frequency within the passband of the nerves. It incorporates a novel compact power oscillator which is normally quiescent until applied to a load, to produce, under load, a waveform which has a unique application to self-protective devices and medical uses. The oscillator includes a high gain inverting amplifier, preferably a Darlington pair constituted by a germanium output transistor driven by a small signal transistor, a transformer, a D.C. source such as a battery, and a pair of output electrodes.