Radio Broadcast (Nov 1926-Apr 1927)

38 RADIO BROADCAST NOVEMBER, 1926 Radio Broadcast Photograph THE SHIELD Against the rear of the main panel as illustrated here is beneficial since it eliminates the hand capacity effects so detrimental to accurate tuning you have a coil form upon which are wound two sections, one of seventy-seven turns and one of eight turns. These sections are separated by a space equalling the width of four turns. Now duplicate this process, making another identical coil unit. These two units constitute the antenna circuit inductance. By dissolving strips of celluloid in acetone, a cement may be made with which the coils may be fastened to the central support, C, as in Fig. 2. The leads from each coil are terminated as shown in Fig. 3. For the interstage coil system, the proceedure is somewhat the same excepting that the first coil unit has a single winding of seventy-seven turns on it. The second coil unit is wound first with twenty-six turns, then a space equal to two turns, and finally a section of fifty-one turns. The correct connections for the interstage form are shown in B, Fig. 3. It is essential that the turns in each form of a completed coil assembly run in the same direction, as in C, Fig. 3. The manner in which the coils fit into the circuit is illustrated in D, Fig. 3. Returning to the wiring, we note that the grid condenser is mounted directly on the detector socket. This insures the shortest possible connection. Reference to the wiring diagram and circuit diagram, Figs. 8 and 7, will show that very simple connections are made to the radio frequency choke coils. Also, the neutralizing condenser is so positioned that short leads are all that are necessary to wire it correctly into the circuit. Three blue wires are twisted together and connected, one to the G post of the first audio transformer, another to the F post of the same transformer, and the third to the G post of the first audio socket. These wires, in the form of a separate cable, are passed along the front of the transformers to the left hand edge of the base board, thence along it to a position at the Radio Broadcast Photograph FOR CROSS REFERENCE This from-above-the-baseboard view should be studied in conjunction with the diagram Fig. 5. This picture shows very clearly how well spaced the various units are, and gives an excellent idea of the cabled filament wiring Remove the chemical coating from the celluloid film by washing in hot water. Then wrap this sheet around the mailing tube to form just one layer, cutting away the surplus. By applying acetone along the seam formed by the celluloid edges a complete cylinder of celluloid will result. From this point on it is better if two people do the job, one to turn the cylinder, the other to guide the wire. However, before the wire is started on the form, lightly coat the entire surface of the celluloid with acetone. This will produce a sticky surface in which the wire will find a substantial hold. From time to time as the wire advances along the form, it may be found necessary to freshen the surface by additional coatings of acetone. Wind about seven inches of wire on the form and set it aside until the celluloid has become hardened again. Then, starting at one end, count seventy-nine turns and lift up the wire at the 79th turn with a knife blade and cut it. Then, unwind back toward the starting point, two turns, so that there are exactly seventyseven turns in this one section. Beginning again where the wire was cut unwind two more turns. This produces a space four turns wide. Count out ten more turns and cut the wire. Unwind two turns to form a lead, leaving eight turns in the second section. With a pen knife cut the celluloid form at the eighth turn and Radio Broadcast Photograph ATTENTION TO THE LAYOUT Is an important factor that is often overlooked in construction of a new receiver. The wide baseboard of the "Lab" Receiver enables all the apparatus to be placed to best advantage. Note the cabled filament wiring which runs right around the base board to the switch and rheostat