The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 156
ete connections for a superimposed circuit at the test boardand section are shown in Figure 118. It will be seen that five sets of fourtest holes are taken up at the line test box (see Chapter XXIV.). Thetwo circuits upon which a + i circuit is superimposed are marked circuitsI and 2. Circuit No. i… … CcT.ZCO/mf-) Figure 118. will at once be obvious that ringing will have to be done by means of thegenerator, since there is no direct connection between the switch-springand the circuit. A non-polarised indicator relay is substituted for the usualpolarised relay, and the batteries which would be…
Telephone · Postal service
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