Radio broadcast .. (1922-30)

368 Radio Broadcast N y Antenna Detector • . 1% r ! 0 — #* 00 ,_ O.L II O ^-.,25 Turns O — y 0 / O15 Turns ^^1 in Tnrnc * Phones Ground FIG. 2 How the different parts of the receiver are connected. The heavy wire in the antenna circuit should not be smaller than No. 14 will be determined by the length of the switch arm. Each end of the box is drilled according to the right hand sketch in Fig. 3. These holes are for the binding posts. Care should be exercised in drilling the box in order to avoid splitting. The metal drills are much preferred to the gimlet. The drills should be sharp and turned rapidly but with little pressure. This procedure will result in clean, unchipped holes. After the required holes are drilled, the pencil lines should be erased by sandpapering and a coat or two of stain can be applied if desired. THE COIL WHILE the stain is drying — or perhaps while the paper is being soaked from the box — the coil can be wound. If the builder prefers, the winding form can be bought for a few pennies from the same ten-cent store that supplied the rest of the parts. But it is easily cut from stiff card-board in exact duplication of the drawing in Fig. 4. It is wound with 45 turns of wire, over three, under three, with taps taken with yth, i4th, and 2ist turns. Over three under three means over three spokes of the spider-web form, and under three spokes, as illustrated in Fig. 5. The turns are wound tightly. After seven turns are wound, a loop about three inches long is twisted forming a double lead. This constitutes the first tap. The winding is continued, additional taps being made, as directed, at the I4th, and 2ist turns. In connecting the set, looking at the panel from the rear, the start or lower terminal of the coil leads to the first switch point (from left to right), the ist tap to the second switch point, the and tap to the third switch point and the 3rd tap to the four or right hand point. The outer end of the coil leads to the antenna post. Loops are made in the tap leads, and the enamel scraped off, so that contact will be made with the nuts on the switch points under which they are placed. Fig. 6 shows how the taps are twisted and connected to the switch points. r ^ Holes For Condenser _4. Holes'For Binding Posts BOTTOM OF BOX EACH END OF BOX FIG. 3 How the holes should be drilled. The condenser and switch point holeJ are most easily Two binding-post holes are 'drilled in each -end of the box " Panel layout." placed with a pair of dividers or a compass.