|The Gower-Bell telephone remained the Post Office choice for many years, and was continuously developed. By 1891 it had become known as the Universal Telephone, so-called because it could be adapted for use under practically any conditions likely to be met with in Post Office service. It retained the Gower Transmitter but the receiver and speaking tubes had given place to a pair of Bell receivers. The calling signal was a trembler bell which was rung by a battery at the subscriber’s premises under the control of a relay operated by a signalling current received from the exchange. A feature of this system of working which has a modern sound was that when an operator rang the subscriber’s bell she could hear the interruption in current caused by the trembler bell contact, a forerunner of ringing tone.
See also History of BPO Telephones
Last revised: May 23, 2014