. American telephone practice . CLOSED. the talking apparatus are alternately brought into service. It willbe seen that when the hook is raised the conditions shown in exist. When, however, the hook is depressed the transmittercircuit is open, as is also the circuit of the impedance coil, while thereceiver is short-circuited; the only circuit across the line is thatthrough the bell and the condenser in series, which is the conditionrequired by modern central office circuits. The various Bell companies employ in their ringing circuit a COMMON BATTERY SUB-STATION EQUIPMENT. 311 bell woun
. American telephone practice . CLOSED. the talking apparatus are alternately brought into service. It willbe seen that when the hook is raised the conditions shown in exist. When, however, the hook is depressed the transmittercircuit is open, as is also the circuit of the impedance coil, while thereceiver is short-circuited; the only circuit across the line is thatthrough the bell and the condenser in series, which is the conditionrequired by modern central office circuits. The various Bell companies employ in their ringing circuit a COMMON BATTERY SUB-STATION EQUIPMENT. 311 bell wound to iooo ohms and a two-mocrofarad condenser. Thisarrangement gives thoroughly satisfactory results and has beenlargely adopted among the various Independent companies. It isfound, however, that almost equally satisfactory results may beobtained by the use of a 500-ohm bell with a two-microfarad con-denser. When, however, the capacity of the condenser and theresistance of the bell are both materially reduced from that of the. FIG. BATTERY WALL SET-OPEN. 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 fron
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