comment; the 500-watt resistance may be taken from an electric heater or the heating element from a flatiron may be used. The aluminum electrode is always positive; see that this is connected through the switch so that it goes to the positive terminal of the storage battery. To charge the battery, throw the switch arm over to the connections to the rectifier and turn on the 110-volt a.c. lighting circuit; the charging rate will be about 2 amp. an hour. When the charge is completed, throw the switch arm over to the opposite side, connecting the battery with the receiving set, and turn off the current. Ten to twelve hours will be sufficient to charge the battery even from a low hydrometer reading. Keep the rectifier as cool as possible and occasionally scrape off the white coating that forms on the aluminum electrode if a solution of borax is used. We have prepared a large blueprint showing the various steps in the construction of both units and suggested hookups. This may be obtained from Popular Mechanics radio department, 200 E. Ontario st., Chicago, for 25 cents, to cover cost and mailing. Specify blueprint No. 126.
Homemade Fuses on Battery Cable
Any Radio Owner Can Provide Protective Fuses in the Battery Cable
When a set of radio tubes are accidentally burned out or the batteries are short circuited and discharged, the radio owner begins to think of safety-first methods and ways of preventing these expensive accidents. In the drawing is shown a fused battery cable. This will give protection to the tubes and it is easily and quickly made. About 1 ft. from the end of an ordinary battery cable, the braided covering is removed, leaving the insulated battery wires exposed for about 2 in. In the center of each of two large bottle corks, a hole is drilled to permit the corks to slide over the cable. They are then fastened on the cable with glue at the place where the braided covering was removed, the exposed battery wires being between the two corks. For the fuse base, a small piece of bakelite is cut and drilled as shown in the drawing. Small brass clips, to hold the fuses, are fastened to the base with screws. These clips make it easy to renew the burned-out fuses. The B-negative and A-positive leads are cut and connected to the fuse clips. Fuses are made from the tinfoil that comes wrapped around candy and chewing gum. It is cut in strips, 1⁄16 in. wide, for the A-battery fuse, and about 1⁄32 in. wide for the B-battery fuse. A bakelite cardboard tube is used for a cover; this slides over the corks and protects the fuses from accidental breakage or from being short-circuited. The cover is held in place by small wood screws.—R. J. Williams, Chicago.
Ball-Antenna Kit
It is claimed that radio reception can be improved considerably by using a ball antenna of the kind shown in the illustration. This outfit comes in a kit and can readily be assembled and installed by anyone. It consists of a bracket, glass insulator and a hollow aluminum ball, 10 in. in diameter. Being non-directional, several of these can be installed on an apartment roof without interference. Selectivity is another advantage claimed for this type of aerial.
