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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 309
Tone Control Relay kTd-rcS6- B To Pilot Relay ; tone signals. (Facing Page 284) 11 Stlf*u*[/atf *Telephone
Internet Archive · California Digital Library · Public Domain Mark 1.0. Free to use for anything.
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