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 106
Fig. 3,048.—Type R F acousticon suitable for those who lose most of the words in conversingwith one person, even when the voice of the speaker be raised. This type cannot be wornupon the clothing. The transmitters are mounted in a black leather covered case, and whenclosed for carrying, the… … Fig. 3,049.—Type R A acousticon fitted with sound regulator and especially adapted for mensuse. The battery and transmitter make one part and the earpiece the other, the two beingconnected by pliable, silk covered wire: The battery can be concealed in the vest pocket,the receiver appearing just…
Electrical engineering
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