High Frequency Apparatus Page 184

184 HIGH FREQUENCY APPARATUS dye. All paints containing lead and carbon must be shunned in the treatment of this apparatus or electrical "leaks" will be developed. There are several good black dyes on the market soluble in water or alcohol and any one of these may be used with impunity. After the surface of the cylinder is blackened and thoroughly dried, it may be given a coat of shellac, when it is ready for winding. The winding is best done in a screw-cutting lathe as the turns are to be evenly spaced 12 to the inch. If the lathe is not available, an improvised winding machine may be constructed with the aid of two bearings to support the cylinder and a length of rod threaded 12 to the inch arranged to turn with the cylinder and to carry a guide for the wire as it is wound. The winding is of No. 22 D.C.C. magnet wire and the first turn is started 1 inch from one end of the cylinder. From this point it continues to within a like distance of the opposite end. A band of 3/4-inch copper ribbon is then placed around the remaining space at either end and the starting and finishing ends of the winding are soldered to the bands. The latter should not completely encircle the cylinder but a gap of ¼ inch should be left where the ends meet. The winding is to be given four coats of shellac, each coat being permitted to dry thoroughly before applying the next. A brass bushing, having in it a hole tapped 3/8-18, is to be firmly secured in each head of the cylinder and connection made from the copper bands to the bushings. Wooden discs, 21 inches in diameter, are to be fitted to the ends of the secondary cylinder in order to give it a finished appearance. Holes are bored through the centers of the discs, of course, to permit access to the bushings within. The secondary cylinder is surmounted by a discharger composed of a brass ball mounted on the end of a rod