Radio Broadcast (May-Oct 1925)

56 Radio Broadcast adjacent layers. So the diamond weave is produced. For the second and third radio-frequency couplers, the primaries must be double-wound to provide the neutralizing winding which is connected to the grid of the tube through the neutralizing condenser. In winding the double primary it is well to have two spools of wire, one preferably colored so as to facilitate identity of connections. Six and one half turns of the pair of wires are wound for the primaries of the second and third couplers. This ratio was selected after tests were conducted where 12 and 18 turn primaries were employed. The antenna primary consists of a single wire wound for six and a half turns. After the primaries are wound, the secondaries are wound directly over them for fortyfive turns in the same fashion and in the same direction as the primary. The inside lead or beginning of the secondary is started several spokes away from the end of the primary so that the leads are not too close together in the finished coil. The coil may be painted with a solution as a binder which has been prepared by dissolving celluloid in acetone, or other "dope" of this nature. The best coils are made without dope and their turns are held in place by lacing made of ordinary grocer's white cord. To remove the coil from the form, withdraw all the spokes and then slide the coil off, taking care to prevent it from coming loose. Fig. 9 shows how to insert the mounting screw so that the coil may be fastened to the brass bus bar running the entire length of the receiver. The outside turn of the secondary connects to this screw. The brass bus bar constitutes Coil Shows position of Insulating Sleeve COIL FORM (Fibre, Celluloid or Hard Rubber 1/2 wide) Diamond Weave Coil "Insulating Sleeve --Threaded Support Bushing Mounting Screw -"?S|x (to which is connected Outsiders 'lead) Panel Brass Bus Bar-' FIG. 9 How the coil is mounted on the brass bus bar strip Brass Bus Bar METHOD OF ASSEMBLY OF CONDENSER, ANGLE BRACKET, COIL AND TERMINAL BOARD FIG. 10 All the parts are sustained by means of the panel and angle brackets the negative or grounded line of the entire circuit. As may be seen from this sketch, the mounting screw is securely fastened to the coil by means of washers and nuts. If it is obtainable, a piece of bakelite or fibre tubing y% inch in diameter may be slipped over the mounting screw to insulate it from the coil winding. The narrow strip of hard rubber or celluloid used as a coil form and inserted after it is wound is also fastened underneath the head of the screw and washer. The coil support may be a larger-diametered piece of tubing or a brass rod may be turned down if the machinery is available. But as little metal as possible should be used in the direct field of the coils. ASSEMBLY WITH the panel drilled, the coils wound, and all the other material on hand, the job of assembly may now be started. First the sockets, then the rheostats and finally the condensers are mounted on the panel. It is well to state here that the assembly directions as outlined only hold good for the material as listed. When other parts are used, the builder must employ his own ingenuity in producing an arrangement as nearly like that described as possible. Looking at the back of the panel, the lower right screw of the right and center condensers holding the end plate of the condensers to its frame is removed. Also the lower screw of the left condenser is removed. Brass angle brackets x 1^ inches x § inch are fastened, as shown in Fig. 10, to the condensers at the places where these screws have just been removed, by replacing the screws securing the brackets at the same time. It is absolutely essential that these screws be