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31.01.2014

Stopper Telephone Exchange with 20 Lines

A new exhibit has been added to the Museum of Telephone History – a 20-line stopper telephone switchboard.

The switch is local battery fed. It has a cast iron base embellishing a ‘coat of arms’. The device was used in both civilian and military organizations. It was produced by ‘Kungliga Telegrafverket Verkstad’ (Royal Telegraph Agency) in Sweden in 1897. It resembled the legendary sewing machine.

The telephone switch was used to connect (switch) subscriber-, connection- and long-distance telephone lines. Technologically speaking it was operated as follows: the subscriber hand-cranked the telephone, which then set a small generator into action, resulting in 60 volts between the telephone line wires and the switchboard. Thus, on the telephonist’s switchboard, a blinker (calling valve) opened automatically. The caller had to say something like: ‘Madam, Solyanka, two-seventeen’. This meant that the girl needed to thrust the plug on the other end of a cord into the seventeenth slot of the second row of the panel (i.e. the panel for the Solyanka region). The young lady then inserted a polling plug into the slot of the ‘called’ subscriber and called out her personal number (as surnames could be difficult to pronounce). The subscriber then specified the receiver’s details. Now the second plug was inserted into the slot of the ‘called’ number. That is how connecting subscribers was performed. At the ‘receiver’ end, a telephone ringer would go off. Having made sure that a connection was established and the two people were talking, the telephonist would then switch a key to the neutral position, ready to accept the next call. Having completed the conversation, the original ‘caller’ had to call once again (by cranking the handle), this time triggering a release valve on the switchboard. It would open, thus signaling to the telephonist that the conversation had ended and had to be disconnected.