. American telephone practice . EN. Bell standard a decided falling off in efficiency is found; for instance,a 500-ohm bell with a one-microfarad condenser, while operative,does not give satisfactory ringing with the average central officegenerator. Many of the Independent companies are thereforeusing a two-microfarad condenser with a 500-ohm bell, the bellbeing of the usual long-core type and wound for a maximum num-ber of turns by using as large a wire as the winding space willpermit. 312 AMERICAN TELEPHONE PRACTICE. As illustrative of the arrangement of parts in a modern commonbattery wall
. American telephone practice . EN. Bell standard a decided falling off in efficiency is found; for instance,a 500-ohm bell with a one-microfarad condenser, while operative,does not give satisfactory ringing with the average central officegenerator. Many of the Independent companies are thereforeusing a two-microfarad condenser with a 500-ohm bell, the bellbeing of the usual long-core type and wound for a maximum num-ber of turns by using as large a wire as the winding space willpermit. 312 AMERICAN TELEPHONE PRACTICE. As illustrative of the arrangement of parts in a modern commonbattery wall telephone, that of the Kellogg Company may be takenfrom among numerous good designs. This is shown in Figs. 261and 262, the latter figure showing the box opened for inspection orrepairs. The ringer is mounted on the movable portion of thebox, connection to it being made through the hinges. The hookretardation coil and various binding posts are mounted on the frontface of the condenser receptacle, which is permanently secured to. FIG. 263.—DETAIL OF HOOK AND CORD MOUNTING. the back board. In order to allow the box when opened to swingclear of the hook lever, the hook escutcheon is split, part of it beingsecured to the condenser receptacle and part of it to the movablebox. The receiver cord is carried through a hole in the stationarypart of the escutcheon, in order to prevent its being pinched by acareless closing of the box. These features are well shown in CHAPTER XX. THE COMMON BATTERY MULTIPLE SWITCH-BOARD. In the development of the common battery multiple switch-boardthe tendency has been, on account of the great cost of the multiplejacks and cables, and further, on account of the ever-increasing ne-cessity to economize room in the jack space, to simplify the multiplejack, reducing the number of its contacts and the number of wiresfor each line in the multiple cable. We have seen that in the oldbranch-terminal magneto-multiple board each jack had five con-tacts, t
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