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 124
when the wiper shaft ro-tates off the tenth set of contacts of any level. One part of the setgrounds the 1300-ohm winding of the ring cut-off relay to cause it to pullup and lock, the other part switches busy tone into the positive wind-ing of the line relay, by which device the calling subscriber…
Telephone
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