. The telephone system of the British post office. A practical handbook . Figure 93. Combination Key. 109 The insertion of a peg at the section drops the visuals at the sectionand transfer board. The operator depresses the combination key, thusconnecting up her telephone. Having ascertained the nature of theservice, the corresponding peg is taken up and inserted into a Bcircuit of the required section. The combination key is then raised, thusputting the visuals at normal. The B circuits are accommodated uponthe upright part of the transfer board. The combination key consists of thirteen spring
. The telephone system of the British post office. A practical handbook . Figure 93. Combination Key. 109 The insertion of a peg at the section drops the visuals at the sectionand transfer board. The operator depresses the combination key, thusconnecting up her telephone. Having ascertained the nature of theservice, the corresponding peg is taken up and inserted into a Bcircuit of the required section. The combination key is then raised, thusputting the visuals at normal. The B circuits are accommodated uponthe upright part of the transfer board. The combination key consists of thirteen springs arranged in two two sets are placed opposite each other, with a round piece ofebonite, controlled by a lever, playing between them. In the normalcondition the springs are as shown in Figure 96. The upper long springs. are connected to the A circuit, and the outer ones to the operatorssecondary; thus when the ebonite moves upwards and pushes apart thelong springs, the operators telephone is connected to the circuit. Atthe same time the central pair of springs make contact, thus com-pleting the operators primary circuit. This is shown in the upper partof Figure 94. The inner spring on the left is not used at all. Thebottom springs are arranged exactly like a ringing key, and when theebonite descends, forcing the long springs apart, they leave the innersprings and make contact with the outer ones. Of these six springs onlythe right hand three are utilised. Tbe effect of depressing the key is no Principle of A Circuits indicated in the lower part of Figure 94. The mechanical design of thekey is illustrat :d in Figure 95.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
