The D-501 Cassette Demagnetizer utilizes a DC-DC converter
with a 1.5 Volt power source system, control and trigger sections. The built-in
electronic circuit creates a pulse signal which is passed through the
oscillator, then amplified. When the D-501’s head is activated by the tape
decks head, this amplified oscillation field then discharges across the tape
head, thus removing the tape head’s residual magnetism.