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Magnetophone Construction. As shown in figure 215,
the magnetophone consists of a magnet and the assembly for the coil. The
magnet is cylindrical, and has two concen-tric poles with a small gap
between. The magnetic field in this gap is 9,000 gauss. The coil assembly is
a group of zinc fittings bolted onto the gap end of the magnet. Inside the
assembly, the coil is mounted on an aluminum block supported by two flat
bronze springs. The coil is wound on a cylindrical paper form and held to it
by shellac. Two springs are used to assure that motion of the coil between
the magnet poles will be along the axis of the coil. A zinc strengthening
strip is bolted on the bottom. When the magetophone is held in fixed
position before the release fuse blows, a pin fits through a hole in this
strip to hold the aluminum coil-mounting block aganist its limit stop and
pre-vent damage due to impact. The system is designed to have a resonance of
22 cps. The mass of the magnetophone and the length of the suspension are
the principal factors in determining this frequency. |
