GPO Telephones - Plan 5 and Plan 7

Plan 5 and Plan 7

This was the GPO's first attempt at a compact, supervised extension plan, for small businesses. The Plan 5 had 2 extensions plus the control station, the Plan 7 had only 1.

The main operator control units, of these plans, appeared similar to a 232 plus Bellset 26 combo but was now a Tele 248 plus Bellset 39a (early versions) or 44 (later). These bellsets had a recess, in the front, dominated by a horizontal, quadrant mounted, 4 position slider, flanked by either 1 or 2 press buttons, for buzzing the extension(s). These Bellsets 39a and 44 were bellsets in name only, as they contained no bell. What they did contain was a maze of spring contact sets, mainly activated by a cam at the pivot of the slide switch. The system required a separate, remote mounted bellset, for incoming signalling. The main unit could make and answer exchange calls, talk to and transfer calls to the extension(s). The extensions could call and talk to each other and the main unit, but could only make external calls if a request to the operator, for the exchange line, was honoured. When this system was eventually revisited and brought up to date, with the 700 series Plans 105 and 107, the equivalent control unit was dubbed 'The Planset'.