Page:Popular Mechanics 1928 01.pdf/136

 



An efficient radio ground, having a "discharge area" several times as great as a driven ground, is now available. Its walls are of heavy sheet copper, rolled into the shape of a truncated cone. A 20-ft. length of heavily enameled lead-in wire is provided, and its connection to the ground proper is made by two heavy spot welds. There are no other soldered or bolted joints and, thus, no electrolytic action is possible. The interior is filled with pure grain charcoal, which absorbs and holds moisture. The device itself, the cap being removed when it is installed, acts as a reservoir for water, providing the lowest possible resistance. Compact and convenient to handle, the unit is installed in a hole bored with an ordinary post-hole auger, no large excavations are required, and the earth adjacent to the ground need not be disturbed. The sketch shows, at the left, the comparatively small area a driven ground exposes to the moist earth and, at the right, the much greater area for discharge obtained with the new type.

 

When trouble appears in the set, investigate carefully, and the chances are that you will quickly find the cause. First examine the batteries, as run-down batteries are the cause of such troubles as the set suddenly losing volume or developing noisy reception. Test the polarity and voltage of all batteries, including C-batteries, and replace any that are defective. Tune in the strongest local station, and if the volume from the loud speaker is still weak, tap the tubes with the fingernail to determine whether or not the amplifiers are operating: if not, a ringing sound will be heard in the loud speaker. Examine all battery connections, and clean any terminal connections that appear to be corroded. If the battery tests have been made and show no trouble either in lack of voltage or defective connections, the next step is to substitute tubes of known efficiency. Try a pair of phones in place of the loud speaker. If no sound is heard in them, remove the tubes from the set and disconnect the A-battery; then, with a pair of headphones in series with a 22$1/2$-volt B-battery, test the grid-to-filament circuits. This is done by putting the terminal of one of the headset leads on the grid contact of the socket, the other phone terminal going to the 22$1/2$-volt battery, while the other lead from the battery is put on the filament contact of the socket. When the contacts are made on the sockets, loud clicks should be heard in the headset, except in the detector-tube socket. Because of the high-resistance gridleak here, a very weak click will be heard or, perhaps, no click at all. Test the transformer windings in the same manner. The secondary terminals are marked F and G, and the primary terminals P and B. If the trouble has not yet been located, replace the tubes in the sockets and put the set in operation. If it is possible to raise a station weakly, press down on each tube successively, and you may find one that is not making good contact in its socket. The remedy is to remove all the tubes and disconnect the batteries, at any rate remove all the tubes; then, with the fingernail or a notched stick pull up all the socket springs to insure a good contact between them and the tube prongs. Polish the ends of the latter and also switch and jack contacts, as corrosion at these points often means the difference between good and poor reception. Finally, look over the ground and aerial connections, or loop connections if a loop is used, and, if the trouble still persists, call in a reliable radio-service man.

