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Bell wire: Difference between revisions
Introduce the bell wire
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With pulse dialling (loop disconnect), the telephone is taken 'off hook', looping the line, and the dialled numbers 0-9 are signalled by the appropriate number of pulses briefly disconnecting the loop - except that 10 pulses are sent for number 0. This causes the audible clicks in the earpiece - in fact, you can count the pulses.
But there's an issue - the brief pulses of disconnection of the loop get seen by the bells of other telephones on the line, which can cause those bells to tinkle as another
== Eliminating the tinkling ==
The tinkling of other bells is irritating, and so the wiring was modified to eliminate it. In the past, bell tinkle was taken by engineers to indicate that the subscriber had installed their own extension wiring - which used to be prohibited, the telephone wiring in the premises was all the property and responsibility of BT. It was only with the introduction of the NTE5 master socket in 1986 that it became permitted to modify your own home telephone wiring.
The modification to the wiring was to locate the bell capacitor in the master socket, and use an additional wire out to all other sockets to drive the bells of all telephones on the line. The bell capacitor in the master socket was connected at one end to the 'B' wire, and at the other end to the new 'bell wire'.
Individual telephones no longer used a bell capacitor, and connected their local bell from the bell wire to the 'A' wire.
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