With manual service, the customer lifts the receiver off-hook and asks the operator to connect the call to a requested number. Provided that the number is in the same central office, the operator connects the call by plugging into the jack on the switchboard corresponding to the called customer’s line. If the call is to another central office, the operator plugs into the trunk for the other office and asks the operator answering (known as the “inward” operator) to connect the call.
Most urban exchanges were common-battery, meaning that the central office provided power for the telephone circuits, as is the case today. In common-battery systems, the pair of wires from a subscriber’s telephone to the switch (or manual exchange) carry -48VDC (nominal) from the telephone company end, across the conductors. The telephone presents an open circuit when it is on-hook or idle. When the subscriber goes off-hook, the telephone puts a DC resistance short across the line. In manual service, this current flowing through the off-hook telephone flows through a relay coil actuating a buzzer and lamp on the operator’s switchboard. The buzzer and lamp would tell an operator the subscriber was off-hook (requesting service).
The switchboard cabinet is wooden and has been through the wars a little since possibly 1920, the front panel with the dials etc is bakelite out of the Mod.
Could use a tidy up , clean and a bit of love.
Dimensions. 74cm widest 77cm deepest 155cm height.
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