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Page:Popular Science Monthly Volume 89.djvu/289

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Popular Science Monthly

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��How a Compact Molded Con- denser Is Built

U. S. PATENT No. 1,174,600, issued to W. J. Murdock, shows the con- struction of the molded condensers which have become familiar in wireless telegraph sending stations. By first fixing in position the plates of the con- denser and then casting them scjiidly into a mixture of pulverized mica and resinous gum, the inventor states that he secures a condenser which is compact, strong, efficient and inexpensive. The drawings show how the two sets of plates a, a, a, and b, b, b, are connected to the terminals e and g by means of the strips d and f. The terminal screws pass through conducting strips h, i, which have their adjacent ends beveled and form a protective spark-gap n. The molded dielectric material, c, is uniform throughout and there are no insertions of mica sheets or other sepa- rators. Units of con\'enient capacity and voltage may be made up and com- bined in series or parallel to meet the needs of any particular transmitting outfit. The condenser has found ex- tended application in portable small- powered quenched-gap senders.

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��Diagram of a molded condenser for small quenched-gap senders

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��Small Radio Stations

HERE are in the United States three licensed amateur stations using only five watts inpud power in their transmitters. Several others use six, eight and twelve watts. It requires about fifty watts to light an ordinary carbon - filament sixteen - candlepower electric lamp.

��Primary Regulator for the Induction Coil The induction coil is shown by A. B represents the battery, and 5 a five- point switch. M-i, M-2, M-3 and M-i^ are magnets from old electric bells. By switching in one or more of these the I)ower used by the coil can be reduced as desired. — C. S. Pokter.

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��An arrangement for regulating the power used by an induction coil

��Cardboard Tubes

A GREAT many amateurs, when mak- ing tuners or loose couplers, are puzzled when they come to the card- board tube problem. They either do not know where to buy the tubes, or cannot make them successfully. How- ever, these tubes can be easily made.

The first thing to do is to get a round cylinder the desired length and diameter and some thin cardboard or thick paper. Wind the paper or cardboard around the cylinder. After the first la\er has been put on coat the inside of the paper with glue to make the layers stick together. After the paper has been wound on to }s or 3 16 in. thick- ness, put elastic bands around the tube to hold it from becoming loose. After the tube has become thoroughly dry take it off the cylinder and coat it with shellac. This process serves to strengthen it appreciably and makes it ready for use. — Albert Killmeykr.

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