. The telephone system of the British post office. A practical handbook . ode, forms the other. A keyupon the transmitter permits of its disconnection, for the purpose alreadymentioned in the case of the switch board telephone. In some types ofthis instrument the switch is replaced by a spring and insulated contactupon the periphery of the case, so arranged that the circuit may bebroken by rotating the transmitter by means of the mouthpiece. A transmitter of this pattern having an oiled silk diaphragm placed atthe end of the mouthpiece in a small circular box at right angles to thetube is now
. The telephone system of the British post office. A practical handbook . ode, forms the other. A keyupon the transmitter permits of its disconnection, for the purpose alreadymentioned in the case of the switch board telephone. In some types ofthis instrument the switch is replaced by a spring and insulated contactupon the periphery of the case, so arranged that the circuit may bebroken by rotating the transmitter by means of the mouthpiece. A transmitter of this pattern having an oiled silk diaphragm placed atthe end of the mouthpiece in a small circular box at right angles to thetube is now being tried, with excellent results. The diaphragm keeps theinside of the transmitter dry, and to clean it it is only necessary to removethe mouthpiece. 88 The Telephone System of the British Post Office. CHAPTER XIV. The a Switch Section. Having now examined every part of the simpler switch section, it willbe well to consider the section as a whole. At the very small offices, wherethere are less than three trunk lines, a section of the A type (Figure 75) a^t juvamtftm. Figure 75. is used. Upon an A switch section three pairs of pegs, with theircorresponding three speaking keys, six ringing keys, and ring-oflf indicators,are fitted. The ring-off indicators are placed at the top of the section,the self-restoring indicators being placed uppermost. Beneath the exchangeSialvanometers come the polarised indicator relays corresponding to the Post Office Subscribers Connected to Trunk Switch. 89 trunks, the corresponding switch-springs for which are at the bottom ofthe board. Next to the trunk relays comes a space for ten polarised dropindicators of the form previously described. Below these are ten five-point switch-springs, which are joined up as shown in Figure 76. Thelines from the subscribers are connected to the outer springs, whilst theinner springs are joined to the indicator. The shutter is held up by the
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
