The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 281
ultiple-magneto exchange, so arranged that an en-gaged test is put on the jacks at the multiple exchange on aring being sent out from the sub-exchange. This is accom-plished by using a differentially-wound relay with a retainingcoil, D.R., in place of the usual differential retardation… … Fig. 265.—Both-Way Junction with Engaged Test and an earthed battery, which lights the calling lamp, C.L.,It also connects the earthed battery to the bushes of themultiple-jacks (of which only one J. is shown), so as to puton the engaged test. The cut-off relay, C.O.R. is of doublemake and break…
Telephone
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