File:Bell telephone magazine (1922) (14753317701).jpg

Identifier: belltelephonemag09amerrich (find matches)
Title: Bell telephone magazine
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company American Telephone and Telegraph Company. Information Dept
Subjects: Telephone
Publisher: (New York, American Telephone and Telegraph Co., etc.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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each subscribers station was a two-point switch, bymeans of which his line could be connected to either his sub-station burglar alarm circuit or to his box telephone, as desired.For telephone operation, during the daytime, the bank vaultor safe at the subscribers premises was short-circuited, thisshort circuit being removed at night, when the burglar alarmsystem was in operation. As will be seen from Figure 3, the system operated on a nor-mally closed circuit, from ground at the substations, throughthe central office galvanometers, G-b, G-d, etc., battery B-2and ground. Subscriber B, desiring to talk with subscriber D,depressed key K-B, which momentarily opened the circuitthrough his central office galvanometer, G-b, causing its needleto deflect and close a local circuit through annunciator A-b andbattery B-Z, operating the annunciator shutter and closing an-other local circuit through vibrating bell V and battery B-2>.Upon releasing key K-B, subscriber B at once moved his sub- 207
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208 THE FIRST TELEPHONE SWITCHBOARD Station switch from the right-hand to the left-hand contact,which disconnected his substation burglar alarm circuit fromhis line and connected in his box telephone, T-B. The ringing of bell V (which was common to all of the cen-tral office annunciator circuits) and the operation of subscriber^s annunciator, notified the operator that subscriber B de-sired to make a call. The operator first silenced bell V (andinsured against its subsequent operation when one of the galva-nometer circuits was again opened or unbalanced) by openingswitch W. The operators next act was to shift plug P-b fromthe right-hand to the left-hand hole, disconnecting subscriber^s central office burglar alarm circuit and connecting the op-erators telephone, T, in circuit with subscriber Bs telephone,T-B. Upon learning that subscriber B wished to talk with sub-scriber Z>, the operator depressed key K-d, which first openedthe circuit through subscriber £)s tap bell, R-D, allowi

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