Abstract: A bulk degausser for erasing a reel of high energy magnetic tape. The degausser includes a circuit for generating magnetic fields including a coil defining a window for passage of the reel of tape. The coil includes a first winding having relatively few turns and a second winding, inductively coupled to the first winding, having relatively many turns. The circuit also includes an ac power supply connected to the first winding and a dc power supply connected to the second winding. A resonance capacitor is interconnected with the second winding for substantially balancing the inductive reactance of the second winding at the frequency of the ac power supply. The circuit also includes an isolation relay, interconnecting the capacitor and the second winding with the dc power supply, for isolating the dc power supply when the first winding is energized by the ac power supply.