c. So far, all of the heads under discussion have been of the electromagnetic type. To further
expand on the erase head, some are constructed to use either a single permanent magnet or a series of
permanent magnets to set up a magnetic field.
(1) If a single magnet is used, the tape is erased by the magnetic flux.
(2) However, with more than one magnet, the tape is erased by the changing cycles of the
(3) The more popular erase heads are those which use a high-frequency current to create an
AC magnetic flux. This current is supplied by the bias oscillator, which also provides the bias current to
the record head, where the magnetic flux lines penetrate the magnetic coating of the tape (fig 3-4). The
AC erase head has fewer turns of wire than the standard playback head, and it passes current easier and
operates better at the higher frequencies.
Figure 3-4. Action of high-frequency erase head