Hawkins electrical guide ... : questions, answers & illustrations : a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications ; a practical treatise (1914)
Hawkins, N. (Nehemiah), 1833-1928 · New York : T. Audel & Co. · leaf 73
in the parallel jack ofthe assigned trunk line. The B operator has only single cords insteadof pairs as has the A operator. The B operator then rings the called number by pressing the ringingkey. The A operator, which is the subscribers direct operator, shouldnot therefore be blamed for unnecessary… … Fig. 2,979.—Buzzer relay as used on P. B. X. switchboards. The magnet winding of thisrelay is energized by direct current which draws up against its soft iron core an armaturewith a contact screw. This screw makes contact, when drawn up, with a spring bladeand closes a low frequency alternating…
Electrical engineering
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