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PBX switchboard, 1975. A telephone switchboard is a device used to connect circuits of telephones to establish telephone calls between users or other switchboards. The switchboard is an essential component of a manual telephone exchange, and is operated by switchboard operators who use electrical cords or switches to establish the connections.
Wiring between system components and telephone sets was facilitated by Type 66 punch-down blocks. For each telephone line from the central office, a key system required five pairs of internal wires: The central office tip and ring leads, the station (telephone instrument) tip and ring wires, the A and A1 control leads, lamp power and lamp ...
1A1A44J5 - Unit 1, Assembly 1, Sub-Assembly 44, Jack 5 (J5 is a connector on a box referenced as A44) 1A1A45J333 - Unit 1, Assembly 1, Sub-Assembly 45, Jack 333 (J333 is a connector on a box referenced as A45) A cable connecting these two might be: 1A1W35 - In the assembly A1 is a cable called W35. Connectors on this cable would be designated:
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When the contacts touch, the switch is closed; when the contacts are separated, the switch is open. The gap must be an insulating medium, such as air, vacuum, oil, SF 6. Contacts may be operated by humans in push-buttons and switches, by mechanical pressure in sensors or machine cams, and electromechanically in relays.
In the 1960s, after the introduction of touch-tone service in November 1963 in various locations of the telephone network, the basic 500-type chassis was retrofitted with a new housing and face plate, and a ten-key push-button keypad. This was designated as the model 1500 telephone, and a twelve-button model 2500 was introduced in 1968.
Beneath the smart-looking buttons, a small converter circuit, powered by re-chargeable Ni-Cd cells, would convert the button presses back to perfectly normal, 10 impulse per second, loop-disconnect dial output, i.e. the new keypad was made to simulate an old rotary dial. But this was the GPO, and nothing was ever that simple.
Arcing horns protecting bushings on a distribution transformer. Arcing horns form a spark gap across the insulator with a lower breakdown voltage than the air path along the insulator surface, so an overvoltage will cause the air to break down and the arc to form between the arcing horns, diverting it away from the surface of the insulator. [3]
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