Page:Popular Science Monthly Volume 91.djvu/174

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158

��Popular Science Monthly

��dimensions shown. The easiest way to construct the pivot is to place the arma- ture in the position it will occupy when completed, and then drill a 1/16-in. hole through both pieces and insert a piece of steel rod of that size. The armature itself is shown at K. This is of soft

���A — Detail of the break key base giving di- mensions for the locations of the parts

iron and can be attached to the armature with one machine-screw.

For supporting the contact-springs a hard rubber crosspiece, L, is employed. This is attached to the armature by a machine-screw. Holes are drilled in it to receive the machine-screws holding the phosphor-bronze springs, M, in place. A brass yoke is attached to the hard rubber crosspiece G, and holds the setscrew for adjusting the play of the armature. In the large end is drilled a hole of such size as to permit a 14/20 setscrew to pass with- out touching. Four smaller holes in the corners are used for attaching to the rubber piece.

A brass strip is bent to the shapes shown at N and supports the contact-screws. These are ordinary 8/32 brass screws. The loop at the upper end of these supports provides an automatic lock nut to prevent the screws from turning when once set.

For the contact-pieces 5/16 in. brass rods with dimes soldered on the ends are used. These are shown at O. If one is willing to go to the expense he can have silver plugs made by a jeweler, but in actual practise it will be found that dimes,

��when filed smooth on the faces, will carry all the current employed in most stations. The shorter contact has a threaded stud which screws into the armature. The other one is made adjustable by means of a setscrew in the hard rubber crosspiece. A good way to get the dimes together in the same plane is to set the brass shanks in their proper places and clamp the two dimes between them and then solder. On separating the pieces it will be found that they are in perfect alinement and meet exactly when the key is in use.

The various parts are assembled on a wooden base of the dimensions shown at A. Heavy binding-posts are mounted as shown in the drawing of the completed instrument and the connections from the moving springs brought down to them by flexible cord. The magnet-leads are brought to the posts in the rear and the main break- contacts to the side posts. The dotted lines are the locations of the magnets and pivot. For setscrews, fillister head brass machine-screws, about 8/32 size may be used.

The connection with the other apparatus is shown in B. The detector in this illustra- tion is shown at D and should be placed as close to the key as possible, since long leads have induced in them currents that are liable to throw the crystal out of adjustment and make the break-in useless. A battery of about ten volts should be used

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��B — The receiving tuner's primary is placed the oscillation-transformer

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��on the magnets. Less would be sufficient but would not give the snappy action so much desired.

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