A power amplifier for use in medical and veterinary testing and therapy. A tunable pulse-width-modulated signal generator is connected to a gating element to provide a digital waveform suitable for comprehensive control of the waveform shape and average output power provided by the apparatus. The digital waveform controls a power driver. Through use of a high-Q resonant circuit including a capacitor and a primary winding of a coil assembly, a voltage of about 150-400 volts is increased to about 10 kilovolts at the primary winding. The coil assembly has a secondary:primary turns ratio of 10:1, resulting in a signal of about 100 kilovolts at the output of the secondary winding. This arrangement produces a corona discharge at a discharge pin connected to the secondary winding. A manual tuning embodiment and a self-tuning embodiment are disclosed.