The practical telephone handbook and guide to the telephonic exchange (1906) (14753808024)

Identifier: practicaltelepho00pool (find matches)

Title: The practical telephone handbook and guide to the telephonic exchange

Year: 1906 (1900s)

Authors: Poole, Joseph

Subjects: Telephone

Publisher: New York, Macmillan Co.

Contributing Library: Northeastern University, Snell Library

Digitizing Sponsor: Boston Library Consortium Member Libraries

Text Appearing Before Image:

purposes, the call being made at the extensioninstrument by lifting the receiver. The three eye-ball signals on the upper row are the clearingindicators, they are connected directly in series in one legof the loop, but are shunted with a two-microfarad condenserfor speaking purposes. When local batteries are used for working instead of powerleads, four separate batteries (of three 6-cells and one 4-cells),are used, connected, as shown by the dotted lines in the left-hand lower corner of Fig. 209, the terminals marked + and-being then unlooped from each other. CHAPTER XIII LARGER SUB-EXCHANGE AND PRIVATE BRANCHEXCHANGE SWITCH-BOARDS The switch-boards so far described have been intended tosupply the wants of small central offices or private exchangesof not more than about 25 lines, where the calls are not con-tinuous, and an operator is not required to be constantly inattendance. For exchanges of more than this number, andup to about 300 lines, a different form of board is required, in

Text Appearing After Image:

Fig. 210 which special provision is made for rapid operating and forthe effective supervision of the connections. Standard Board.—Figs. 212 and 213 give views of a 50-lineswitch-board (arranged for magneto working) as used by theNational Telephone Co. It is worked on the double-cord principle, the cords and plugs being quite distinct fromthe line connection until the plugs are inserted into the line-jacks, as shown in Fig. 210. Each pair of cords is providedwith a tubular drop of 1000 ohms resistance, connected in183 184 PRACTICAL TELEPHONE HANDBOOK bridge or shunt, for clearing signals, and with a combined ring-ing and listening key, as per Fig. 180 or Fig. 182. The subscribers lines are brought through a hole in the topof the board, and are soldered to tabs at the back, these tabsbeing arranged in numbered pairs (or sometimes threes, onebeing left spare for multiple use when the number of boardshas increased beyond three or four). From the tabs whichextend through the board, as sh

the practical telephone handbook and guide to the telephonic exchange 1906 book illustrations telephone electric generators magneto images from internet archive

1906

Northeastern University, Snell Library

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public domain