Page:Popular Science Monthly Volume 91.djvu/457

This page needs to be proofread.


�q Amateur • Electrician

��o\nd Wireless Operator

��An Easily Adjusted Ball-and-Socket Detector-Stand

A' DETECTOR-STAND capable of es- pecially easy adjustment, on account of the ball-and-socket arrangement of the movable arm, is illustrated herewith. The ball was taken from a butt-hinge; a bind-

���The ball-and-socket joint makes an easily adjusted detector for wireless apparatus

ing-post was re-threaded to fit the stud attached to the ball, as shown. The socket is made from spring brass, and holes slightly smaller than the ball are drilled very near the ends. A tension-screw is fitted to the socket, which is three-quarters of an inch long with a knurled nut for easy turning.

The mineral holder is a U-shaped piece of quarter-inch brass rod flattened at the bottom. Near the end of one leg a hole is tapped with an 8/32 tap and an 8/32 thread is also tapped in the bottom of the clamp so that it may be fastened to the base.

The base may be taken from an old spark- gap or cut out of fiber or hard rubber and drilled to suit. It should be about 2 in. by 4 in. The arm is made of Hs-in. brass rod 3 in. long; threaded 8/32 at each end. A binding-post may be mounted on it to carry the "cat-whisker" wire or mandolin- string, or nuts may be used on the arm end for clamping the same as a binding post. — Francis W. Nunenmacher.

��A High Tension Audion Battery Made of Medicine Vials

WHEN using audion or similar tubes, a battery giving from 30 to 40 volts is necessary. Such a battery made up of small flashlight dry-cells is most convenient but costs as much or more than the tube itself. Dry-cells also have what is known as "shelf life." This means that they de- teriorate even when standing idle (on the shelf evidently). In a year's time, more or less, they will have lost their strength and their voltage and current will be near zero. As the high tension current consumed by the audion tube is extremely small, a bat- tery may be madr >ip of very small storage cells, when a direct or alternating lighting current is available for charging them. With alternating current, however, a suit- able rectifier must be used. The battery cells may consist of small medicine vials with strips of roughened lead for plates. Such a battery is shown in the illustration, mounted directly back of the panel holding the tube and voltage-regulating switch. The vials are conveniently mounted in a row between two wooden cleats so that they will not topple over. Small wires are led from the switchpoints and soldered to the tops of the lead strips. The lead strips

���Cells of battery made up of small medicine bottles with strips of lead for the plates

should not reach to the bottom of the vials. A drop or two of light oil on top of the electrolyte will tend to prevent acid fumes from arising and tarnishing parts of the apparatus. When charging with no- volt

��441

�� �