The AA Ultrasonic acoustic probe is designed for use on air insulated terminations where a clear sound path between the electrically stressed insulation and the probe is present. The sensor is extremely sensitive and can detect activity below 10pC. The probe has a magnetic base to allow coupling to steel enclosures and a swivel head as so the detecting sensor can be aimed directly at the HV point. Corona in air and surface tracking can seriously damage high voltage insulating surfaces in a way that will ultimately lead to flashover and complete failure of the insulator. This discharge activity creates acoustic emission that can be detected using a high frequency sensor. The magnitude of the acoustic emission is indicative of the degree and severity of the discharge activity.