G.E.C. "GPO"
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SYSTEM APPROVED BY THE POST OFFICE ADMINISTRATIONG.E.C. P.A.B.X. " G.P.O." system
The final selectors are fitted with "normal post" springs which are mechanically actuated, when the wiper shaft reaches the 9th level, when the digits 9 or 0 are dialled. The operation of these springs causes the manual board extension lamp to glow when the "0" level is reached and the selector is immediately released. Exchange prohibition is provided for by fitting an "EP" relay in each selector. This relay operates when the selector is seized and when a restricted extension dials "9" for "Direct access" this relay will remain operated and N.U. tone is returned to the caller. If an unrestricted extension dials "9" relay EP releases and allows the selector wipers to hunt over the 9th level for a free line to the public exchange. When a free line is found the selector is converted into a "straight through" connection and the extension can dial through the public exchange equipment direct, if automatic, or if manual, speak with the public exchange operator when she answers. Far direct access service, exchange lines are equipped with both way repeaters which can be modified to provide "through clearing" conditions if the public exchange is converted at any time from manual to automatic. This equipment is inserted in the public exchange line via a "night" jack. When "night" service is required a plug is inserted into the exchange line night jack and an extension can then be connected direct to the public exchange, the other plug of a pair being inserted into the extension night jack. The auxiliary equipment is disconnected from the exchange line and made to test engaged to other callers who may endeavour to dial via "direct access."
Alarms Release magnet alarms are also provided which control the "auto-urgent" alarm lamp at the manual board. A blown fuse also lights the "auto-urgent" alarm lamp at the manual board. If the ringing machine fails to start up, a "ringing failure" lamp glows at the automatic equipment and the "auto-urgent" alarm lamp glows at the manual board. The manual board is fitted with alarm lamps, i.e., auto urgent and manual urgent, the latter for manual fuses and provides facilities similar to the Post Office 10+50 type. The alarm lamps can be disconnected by operation of the "night service" keys. Trunk offering Numbering scheme The automatic equipment is mounted on a rack 6' 6" high, 2' 8" wide, and 1' 6" deep, forming one unit. The main fuses, apparatus fuses, rack alarm lamps and tag blocks for wiring are at the top of the rack, and below these are the jacked-in final selectors, six in number when the unit is fully equipped. The Line Finder uniselectors are mounted below the final selectors and the assignment (or distributor) and time pulse uniselectors are mounted in the same row. Two relay groups are mounted below the Line Finders, one containing the line equipment for extensions 20-58. The other group contains line equipment for extensions 56-69, relays associated with the line finders, and the assigner; also the alarm relays and a dead level relay group. The two relay groups have removable metal covers. The ringing machine, together with its alarm lamp and "continuous run" switch are mounted at the bottom of the rack. When direct access is provided a special rack is necessary and contains the "bothway repeater" relay sets. Two automatic units, suitably wired and inter-connected, increase the P.A.B.X. capacity to 80 lines, when required for "private purchase" cases. Taken from a paper by the IPOEE dated 1932 (No. 142)
Equipment racks and associated switchboard
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Last revised: June 18, 2022FM | ||||||||
