. Electrical instruments and telephones of the Signal corps . aced on leftside of key board. 99.—Circuits of fifty-drop, Nortli Electric, magneto switctiboard. It has also been found in some cases that the generator armaturesof these switchboards continue to revolve after a call has been made,thus unscrewing the generator handle from the driving shaft. Toavoid this a high resistance will be provided to be bridged across con-tacts Nos. 2 and 3 of the hand generator shown on the circuits referredto above, in order to furnish a slight load for the generator and cause 160 ELECTRICAL INS
. Electrical instruments and telephones of the Signal corps . aced on leftside of key board. 99.—Circuits of fifty-drop, Nortli Electric, magneto switctiboard. It has also been found in some cases that the generator armaturesof these switchboards continue to revolve after a call has been made,thus unscrewing the generator handle from the driving shaft. Toavoid this a high resistance will be provided to be bridged across con-tacts Nos. 2 and 3 of the hand generator shown on the circuits referredto above, in order to furnish a slight load for the generator and cause 160 ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. the armature to stop as soon as the generator handle is released. Arefpiisition should be made for these resistances wherever their use isconsidered to be of advantage. OBSOLETE TYPES OF SWITCnBOARDS. To cover those types of switchboard now in more or less extendeduse,but no longer supplied, there are retained descriptions of the wall-cabinet type of 10 and 20 line boards, and of the cordless switch-boards, models of 1001 and WALL-CABINET SWITCnHOARD. The wall-cabinet switchboard is designed for small exchanges,from 20 to -10 lines, Avhere it is desired to save space. The working parts are mounted on a hard-rubber panel in thefront of the box, which is fastened with strong hinges to the back-board. In the 20-drop board, figures 100 and 101, three pairs ofplugs and cords are used, and in the 40-drop board six. The jacksare located immediately below the drops. The upper row of keysserve as listening keys for the pair of cords below them, while the ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. 161 ringing Iveys are located just below the listening keys, each one aboveits own cord. A microtelephone is used for the operators set, andthe drops are supplied with a night-bell circuit. The wiring of thisboard is shown in figure 101. 6 o Dry cells E5~^ ^ Linejacks rv- pii^ Line drops <—*■ ai I 1 m tt
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