Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems (1921)
Smith, Arthur Bessey, b. 1875, Campbell, Wilson Lee · New York : McGraw-Hill · leaf 401
the springs of the line relay and its own winding to negativebattery, so that after once attracting its armature, it will not release ituntil both the subscriber and the operator are off the circuit. Thecut-off relay lights the holding lamps shown just above the line-signallamps, so that as long as… … To Oper Fig. 296.—Trunk incoming to an information position from selector switch banks. Occasionally information boards are arranged with the trunks endingin jacks instead of keys. The circuits of a jack-ending trunk are shownby the dotted lines in Fig. 296. Dead-number Trunks.—These trunks are…
Telephone
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