The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 237
Fig. 238 … Fig. 239 half the resistance of one coil. In his later patents two suchsingle coils are used, and both are wound on the same core, asshown in Fig. 239, this constituting what is now known as a toroidal coil or repeater. The action which takes place when speaking is as follows :—■The current from…
Telephone
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