. Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems . Fig. 157.—Private branch exchange switchboard. Fourth Class—Manually Operated Private Branch Exchange Switch-boards Using Cords and Plugs.—A reproduction of a photograph of asingle position switchboard of this type with a capacity of about 60lines is given in Fig. 157. This type of board is commonly equippedwith regular cord circuits for interconnecting local lines and for connect-ing them to the trunks; and also with two or three toll-cord circuitswhich are used for connecting up subscribers for through
. Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems . Fig. 157.—Private branch exchange switchboard. Fourth Class—Manually Operated Private Branch Exchange Switch-boards Using Cords and Plugs.—A reproduction of a photograph of asingle position switchboard of this type with a capacity of about 60lines is given in Fig. 157. This type of board is commonly equippedwith regular cord circuits for interconnecting local lines and for connect-ing them to the trunks; and also with two or three toll-cord circuitswhich are used for connecting up subscribers for through calling andlong-distance connections, when talking current is to be fed direct from SUBSCRIBERS STATION EQUIPMENT 161. 162 AUTOMATIC TELEPHONY the toll board or from the switches at the central office. This board hasthe customary supervisory and night-alarm circuits. A general diagrammatic scheme of the circuits is shown in Fig. line circuit is equipped with relay and lamp signals. The regularcord circuit is of the common battery type with double-lamp supervisory lamps operate through a third conductor in the cord. The toll-cord circuit contains no relay except one low-wound super-visory relay connected in series in one side of the cord and bridged by condenser. The trunk circuit is made two-way to economize inthe trunks required and to simplify the operation. The battery current for this type of switchboard is generally fed fromstorage batteries at the automatic central office. A local battery of drycells giving 24 volts is installed at the switchboard and multipled acrossthe pair of wires which supplies current from the central office storagebattery. This in connectio
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttelephone, bookyear19
