Fig. 77.
145. Induction Coil. Fig. 78, 78–A, 78–B. In case you wish to make a larger coil than those already described, the following will be found practical. It is made in the same general way as before, an automatic interrupter, however, being added.
The Core is a machine-bolt, 4½ in. long and 5⁄16 in. in diameter. You may use a carriage-bolt of the same dimensions, if you file away the square shoulder at the head end, so that it will be the same size as the body of the bolt. Paste a piece of thick paper upon the head, so that A will strike the paper instead of the iron. The Washers should be made around a spool that is fully 1 in. in diameter. ([See § 119].) The core should be insulated with paraffine paper before winding on the primary coil. ([See App. 88].) The washers are 3⅞ in. apart, inside. The winding of the coils should be done with [App. 93], or some other winder. The winder-nut, W N, Fig. 70, must hold the long core perfectly tight, to avoid wobbling. The base is 8 × 5 × ⅞ in. The different parts are placed as shown. The coil is fastened to the base as in [App. 97]. For binding-posts see [App. 46].
Fig. 78.
146. The Primary Coil ([§ 137]) is made by winding 3 layers of No. 24 insulated copper wire upon the insulated core. One end, 6, is fastened to W ([See § 109]), and the other end, 5, is held under the screw-head, R. Wind at least two layers of paraffined paper around this coil before winding on the secondary coil.