Radio broadcast .. (1922-30)

244 Radio Broadcast tube socket has been added and the new twocoil mounting is indicated on the diagram (Fig. 1 1) and at the extreme left in Fig. 12. Fig. 1 1 has been drawn with the apparatus shown in the exact position from left to right that it occupies on the panel. In Fig. 12, note the jack installed at the right in which a loop may be plugged. The coils in Fig. 1 1 (DL-y5o) are both shown in the photo (Fig. 12) as variable, but DL-75O has been found to be the proper size. The installation of the two-coil mounting allows the output to be fed to an intermediatefrequency amplifier. LEAVES FROM AN OLD TIMER'S NOTEBOOK Amplifier Squeal In The Last Stage: This annoyance is often encountered in using a third stage of audio amplification, and, occasionally, FIG. 13 A fine vise of the approved type. Note the massive construction, and the two guide bars on the second stage. Every metallic object in the immediate vicinity of the set, but not electrically connected to it, should be grounded. The high voltage wires (those running from the B battery) should be run in grounded lead covering. Specific instance: Third stage of amplifier possessed a very high (in the upper limits of audibility) squeal, a persistent peanut whistle which was more nerve-racking than if it had broken up the signals. All wiring was run in lead-covered duplex which was grounded. Instruments were perfectly spaced, shielded in places, and of the best electrical design. Special telephone cam switches were used for cutting out amplification stages. As a last resort, the metal frames of the switches were connected together and grounded. The squeal stopped ! BUILDING YOUR OWN LAB RADIO BROADCAST'S suggestion for this month's addition to the budding laboratory is a vise — but not of the five and ten cent store variety. The experimenter should pay about two dollars for the vise. It should be of a reliable, well-known make. It should have steel jaws with at least a two-inch separation. A vise of the recommended type is shown in Fig. 13. The vise is one of the most useful tools in the workshop, but one that is often the last thought of by the average amateur, and it is generally not added to his equipment for many months, or even years, after he has accumulated less useful tools. The uses of this "third hand" are so many that -there is scarcely a bit of radio construction in which it will not save time and extra labor, as well as lending accuracy and finish to the completed work. It will hold panels for drilling after one or two instruments are already mounted: It will hold rods and tubing for threading; bakelite, rubber or wood for working and sawing; metal strips, etc., for bending and filing, and many other materials for many similar tasks where a slip means minutes or even hours of additional labor. When used for holding wood, or panel material, for drilling, planing, etc., small blocks of wood should be placed between the jaws and the material, in order to prevent marring under the tight grip of the steel jaws. The vise lends itself to perfect cooperation with the drill, taps and dies which we have recently suggested as additions to the laboratory. RADIO BROADCAST will be pleased to. buy from its readers, at prices from three to five dollars, any kinks, devices, original ideas, etc., with photographs if possible, which the Editor may consider eligible for this department. Address all communications to the R. B. Lab Editor.