Space Age Crystal Set

A sun-powered transistor amplifier makes this a—

By D. S. Halacy Jr.

LIGHT-POWERED RADIO plays indoors under artificial light, too. Performance is boosted by connecting antenna to TV aerial or telephone-dial finger stop; a short length of wire, with alligator clips at the ends, helps.

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HIS tiny radio puts satellite technology in the palm of your hand. Like radios in artificial moons, it's powered by the sun—or any other light. Basically, it's a 1960-model crystal set. A rugged sealed-in-glass diode has replaced the shaky catwhisker and galena crystal. The usually faint crystal-set sigAuthor Halacy is an expert on the. sun. A couple of years ago he wrote Fabulous Fireball, a book that tells the story of the sun and solar energy. Last fall. Macmillan also published his Fun with the Sun. a book describing how to make seven solar-energy projects at home. The present, article is an outgrowth of his research for the latter book. 170 POPULAR SCIENCE JANUARY 1960

nal is magnified many times by a transistor, in turn powered by a high-efficiency silicon solar cell. This unit—and other parts—can probably be obtained locally for less than five dollars. All are standard parts, stocked by most retail and mail-order shops. In a pinch you can substitute the less-efficient International Rectifier B2M selenium cell for the quarter-round section of a Hoffman silicon solar battery. First steps. Best place to begin construction is with the case for the radio— a small plastic box. You may find one in the medicine chest or at the druggist's. Start the necessary holes with a hot ice pick, then file or ream to size Keep try-

ing the part as you enlarge the hole, to insure a snug fit. The case can be painted or left transparent. The one pictured has a finish of Day-Glo spray paint, applied to the outside of the case. The paint softened the plastic slightly and created a wrinkled finish. The hinged top is left clear and a piece of painted bond paper cut to fit inside. This paper was lettered, and cut to accept the dial shaft and solar battery. The lettering is pure whim—there's no trademark or commercial name. After painting, go ahead with the assembly. Set the antenna mounting base through the bottom hole, put on the nut,

cut off excess threads, and file smooth. Add a 6-32 screw and nut to the other side if you expect the radio to stand up. Condenser and battery. Install the tuning condenser in the hinged top by first removing the dial and the small flathead screws. Remove both hex nuts; use one on the outside to hold the condenser in place. Then mount the dial and twist the silver center screw thumb tight. Place the solar battery in position over the opening in the bond paper, and fasten it in place with a strip of cellophane tape. Bend the loopstick mounting bracket as shown, snap the loopstick in place, and fasten the bracket with a 6-32 screw and [Continued on page 230]

Space-Age Crystal Set [Continued from page 171]

nut. Install the phone jack, and the radio is ready for wiring. Use stranded hookup wire; it can take the flexing imposed by opening and closing the case. Pitfalls for amateurs. The wiring shown in the drawing is straightforward and follows the circuit schematic. If you're familiar with electronic wiring, you'll probably find some short cuts. If you're a beginner, stick to the diagram. If you run into trouble, don't hesitate to remove the parts, do the soldering outside, and then replace them. Use care when soldering the diode and transistor—excess heat will damage them. Sidestep part of the risk by soldering to the lugs of a transistor socket, then slipping the transistor in place. You'll have to clip the transistor's leads to make it fit. Bend the diode's leads to fit before soldering it between the base of the transistor and the loopstick. Close the case when you've finished soldering, plug in the earphone, and listen. There's no on-off switch: The battery never wears out. You should pick up stations at their proper position on the dial as indicated by the point of the battery or a dot on the lid. If the calibration is too far off, make a hole in the end of the case in line with the slotted screw on the loopstick. Turning this screw one way or the other will shift the stations enough to align the dial. Outdoors, you'll find you don't have to point the Solar Mite at the sun—there is plenty of incident light for satisfactory operation. Keep the whip upright for maximum volume. For stronger signals. Touching the silver center of the tuning dial may give you a stronger signal, since your body acts as a ground. Also try wetting your finger before touching the dial. While the Solar Mite will play on the whip antenna, for peak performance connect the whip to your TV antenna. If you don't have an outdoor antenna of any kind, clip a lead on the finger stop of a telephone dial. You'll find that the radio works well enough to bring in a strong station even in the dark—acting as a crystal set without the help of its transistor amplifier.