It consists of a small
induction coil that can be constructed at home.
The core of the coil, A, Fig. 1, is constructed in the usual
manner, of small soft-iron wire to make a bundle about 3/16 in. in
diameter and 2 in. long. The coil ends are made from cardboard,
about 1 in. in diameter, with a 3/16-in. hole in the center. The
hole
[Illustration: Details of Induction Coil]
should be cut as shown in Fig. 2, so as to have four small pieces
that can be bent out, leaving the projections as shown. After
wrapping three or four turns of paper around the bundle of wires
the cardboard ends are put on with the projections inside, so the
coils of wire will hold them in place. About 70 turns of No. 24
gauge double covered magnet wire is first placed on the core, for
the primary, and then 1,500 turns of No. 32 or 34 gauge
double-covered wire is wrapped on top of the primary, for the
secondary. Sufficient length of wire must be left outside at each
end of both windings to make connections. The vibrator B, Fig. 1,
and the support C are made from thin spring steel, about 1/8 in.
wide, bent as shown and securely fastened to the cardboard end of
the coil.
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