Nikola Tesla Books
THE CONSTRUCTION OF LARGE APPARATUS 193 Fig. 7. Details of secondary winding showing wooden block or form upon which the wire is wound of wire is separated from its neighbor by two layers of oiled paper which should be purchased in the form of a roll of paper tape two inches in width. As No. 25 wire winds 51 turns per inch it is obvious that there will be a margin of about 4 inch along either side of the layer of wire. The finished secondary is given a coat of armalac and the edges of the paper layers are liberally plastered with the compound in order that moisture may be prevented from entering. After the composition has dried, the secondary may be placed in position on one of the shorter legs of the core. The primary is composed of 100 turns in all of double cotton covered wire. The first 70 turns to be wound should be of two No. 8 wires wound in parallel and the remaining 30 turns should be of a single No. 7 wire. Taps of heavy copper ribbon are to be brought out at 70, 80, and 90 turns in order that four variations of power may be available. The primary may be wound on the same form as the secondary and the insulating core on which it is wound should be built up similar to that on which the secondary was wound. The cord is wound upon the form in order that the coils may be removed without difficulty merely by
