Radio broadcast .. (1922-30)

i8 Radio Broadcast FIG. 5 The tuning units Ta and Ti (left to provided as it reduces signal strength, although at the same time increasing selectivity because the damping effect of the crystal rectifier is effective over only half the inductance; if a vacuum tube detector were used, the value of this connection would be nil, the grid-filament resistance being so high. Although the volume would be diminished, selectivity would be neither greater nor less. In most cases the lead from the positive B terminal of the primary of T3 will be connected to terminal No. 4 of T2 rather than to the tap. Only a very light coat of dope or shellac should be placed on the primary of No. 2 as it is desired to keep the distributed capacity very low. In mounting, T2 should be placed on its condenser at right angles to that of Ti . Fig. 5 shows the correct arrangement which should be followed. The photographs of the back of the complete receiver (Figs. 2 and 6) indicate that the variable condensers face each other; this is not good practice because the dials must then be of different types, one reading left hand and one right h'and. Therefore, in the panel layout, Fig. 7, and in the photograph of Ti and T2 (Fig. 5) corrections have been made so that both condensers are mounted in the same manner and both dials may be of the same type. All stated dimensions have been checked and corrected so that the drawings may be followed with perfect assurance that everything will fit. These special transformers, both Ti and T2, may be purchased if the constructor wishes to save time and labor. They are priced at about S6.OO each. THE VACUUM TUBE STRIP T right) HE vacuum tube socket is "spun" into a sub-panel 3^" x 5" x -IB-" on which are located the filament resistance mounting clips, binding posts, audio-frequency transformer and mounting bracket, but single sockets made for panel mounting may be purchased for about $1.50 and the assembly of the sub-panel will then be up to the ingenuity of the constructor himself. Figs. 10, ii, and 12 will help to show the proper arrangement of parts. In assembling, care should be taken that the audio-frequency transformer is placed with its grid terminal adjacent to Ti ; the plate terminal will then be close to T2 so all leads may be made very short. Four binding posts are located on this subpanel as indicated in the drawing Fig. 8. This is the correct method in contrast to the photographs which show a receiver with a slightly different wiring system. Special attention should be given the springs of the tube socket as "dead" tension will in time cause a great deal of difficulty, chiefly characterized by noisy and spasmodicoperation. THE FRONT PANEL THIS should be of Bakelite, Formica, orRadion, 9" long, -]\" high and vV" to \" thick. Bakelite or Formica should be sanded or grained on both sides, but Radion should retain its original finish. The panel is drilled in accordance with the front panel layout, Fig. 7, but the position of holes may be changed to suit any condensers. ASSEMBLY AT ABOUT this stage in the manufacture of a home made receiver, the amateur workshop, whether it be a real shop, the kitchen, parlor, or attic has assumed an air of congested indecisiveness that hardly bespeaks the usually tidy habits of the constructor; coils, tools, condensers, dirt, sockets, wire, binding posts, solder, and some more dirt and tools are indiscriminately mixed and thrown