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Page:Popular Science Monthly Volume 90.djvu/650

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634

��Popular Science Monthly

��An Inexpensive Tester for an Electric Lamp

THE drawings show how to rig up an inexpensive tester for lamps for use on no, 220 or 440-volt lines. First cut a board as shown in the first sketch, making it about 8 in. in diameter, with a handle long enough for a good grip.

���Lamp sockets on a board cut like a paddle for testing lamps of different voltage

Then locate four lamp-sockets as shown. If the upper end of the sockets are tapped for a ^ in. pipe, cut nipples long enough to reach through the board. These hold the sockets in place.

Binding-posts are located at A, B and C. A hole is bored through the handle of the tester, large enough for the lamp cord and connections, as shown.

The tester may be changed to receive current from any of the three different voltages, by simply attaching the loose end to the different binding-posts, ac- cording to the voltage of the current. In brief: Attaching the end to A makes a circuit for 440 volts, to B, for 220 volts, and to C, for no volts. New globes are used in the tester, and the lamp to be tested is placed in the last socket on its circuit.

��An Emergency Electric Plug Made of Broken Lamp

WHEN the extension plug to the Christmas tree lighting outfit was left loose on the floor, and was kicked into the open grate fire, an emergency plug had to be made in order to hold

��the celebration according to schedule. An old fuse plug was used for this purpose. One wire was soldered to the shell and the other to the brass stud in the center. A disk of fiber with holes for the wires was substituted for the mica. This made a good and serviceable plug, which has been used several times for other purposes. — ^Aaron E. Smith.

��A Mechanical Rectifier as a Wireless Receiver

IT is well known that the power of the high frequency current set up in a receiving antenna, by the arrival of normally strong waves, is much more than enough to operate a telephone receiver. There is no need of amplifying the effects of this received energy; it is merely necessary to convert it into a form which is suitable for the operation of a telephone or other ordinary indica- tor. Since the radio frequency current itself is too high to cause energetic re- sponse of the regular magnetic tele- phone, the conversion need be merely a reduction in frequency; as an alterna- tive, the energy may be rectified into pulsating direct current.

The crystal rectifiers which are used in so many stations serve to distort the current of the received waves so that, as it reaches the telephone, it is stronger in one direction than in the other. Thus for each group of waves the diaphragm is attracted or repelled (according to the polarity of the current pulse) a single time. If sustained waves are received it is necessary to break them

���By changing the speed of the interrupter a musical signal of any pitch can be secured

up into groups, in addition to rectifying, them as just described, if tonal signals are desired. The groups may, for example, be secured through methods involving interrupters, or "beats" pro- duction.

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