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Page:Popular Science Monthly Volume 90.djvu/483

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�Q Amateur • Electrician

��^d Wii'Gless Operator

��Increasing the Spring Tension on Vibrator Adjustments

USUALLY the vibrator of a spark-coil has only one adjustment, and when the parts become worn or the screw fails to do its duty some means must be em- ployed to obtain results. The position of the contact points requires fine adjustment




��coil BOX,

��Paper strips placed under edge of spring-sup- ports to secure fine adjustment of the tension

for the coil to deliver sparks of maximum power. The wear may be taken up by the screw but this will cause a weak tension on the spring.

To overcome this difficulty on the coil I owned, pieces of paper were placed under the spring-support as shown in the illus- tration. This made it possible to obtain afineradjustmentwith the thumbscrew, and eliminated the trouble. — JohxU.Leversee.

��A Concealed Rheostat for Audion Cabinets

OX audion cabinets a rheostat is gen- erally used for controlling the low- voltage battery current. The cabinet looks much neater if the rheostat proper is con- cealed and only a control-handle and pointer can be seen. Such a rheostat may be constructed as folbws: Procure a porcelain-base battery rheostat and remove the stiff brass contact-arm and the center bolt. Make a contact-arm from light sprmg-brass and slip it on a long batterv- bolt; lock it in place by means of a flat battery-nut, place on a washer and then

��insert the bolt in the hole in the center of the rheostat. Place another washer over the bolt, on the back side. The connection with the binding post should be soldered to this washer. Screw on two more flat battery-nuts, adjusting them so that the arm will slide evenly and smoothly over the resistance element, and then lock the nuts by screwing them against each other. Next secure a brass rod 34 in. in diameter and sufficiently long to project i in. from the front of the cabinet when the rheostat is placed against the back of the panel. Such a shaft may be found in some old telephone ringers. Drill a hole in one end of the brass rod and thread the hole to fit the bolt in the center of the rheostat base. Turn the other end down a little in a lathe and thread it so that it will take a battery- nut. Screw a nut on to the bolt on the rheostat and then screw this bolt into the hole in the end of the shaft, locking it by screwing back the nuts. Drill a hole in the panel of the cabinet and insert in this a bushing from an ordinary incandescent- light socket. Insert the shaft and screw the rheostat to the back side of the panel. Make a pointer of brass, about x}/^ in. long and slip it over the small threaded end of

���The rheostat is on the back side of the panel and is operated from the knob in the front

the shaft. Make a handle by cutting a piece of hard rubber, or fiber, J^-in. thick, in the form of a circle i3^ in. in diameter, drill a hole in the center, and place it on the shaft over the pointer. — Frank Sahlman.


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