Lamp Signalling with Auto or CB exchange lines
This private manual branch exchange switchboard, with capacity for four exchange lines, 18 extensions, and seven connecting circuits, has been designed in accordance with modern needs. Compared with earlier types of switchboard, it offers the attractive combination of improved facilities and compact design, both features having been obtained largely through the use of miniature keys and 4 wire extension lines. The switchboard operates from a 50v supply and its physical design features are similar to the 2+6 and 3+12 types in the cordless PMBX range.
Up to half the extension line circuits can be converted to 2-wire working by the use of wall mounted auxiliary relay units of which there are five types for:
Construction and Finish
The switchboard is in two-tone grey. The lift-off cover is a one piece moulding made of impact resisting light-grey plastic, whilst the plastic faced metal equipment panel and the metal base are elephant grey. The front and rear equipment mountings hinged on the base can be opened book fashion for maintenance, as shown in the illustration overleaf. The switchboard is fully tropicalised and uses p.v.c. insulated wire throughout.
Keys are miniature type N9300, with ivory-coloured wedge handles tipped with inserts of contrasting colours to assist ac- curate operating.
The lamps are behind a lens strip held by clips at the ends. When this strip is removed, the lamp-jack assembly can be pulled forward after releasing its fixing screws.
Relays are Types N45000 (BPO 600) and N30000 (BPO 3000), protected by strip covers.
An internal terminal field permits direct termination of incoming lines. Alternatively, for plug-in switchboard connection, a 6ft (1.83m) flexible cord with matching plug can be supplied, together with an associated line jack.
At installations where no source of power ringing exists, a wall mounted ringing
converter, operating from 200-250V, 50Hz a.c. mains, can be supplied. Alternatively, an
inbuilt or wall-mounted transistor ringing unit can be supplied.
The separate two-tone grey table type Etelphone provided for the switchboard operator, can be arranged for use in conjunction with an operator's lightweight headset, if required.
The required 50V d.c. supply is usually derived from the a.c. mains via a battery eliminator.
Full load current drain: 2A without auxiliary unit, 4A with auxiliary unit.
These are Plesseyphones (catalogue sheet 7159) or Etelphones (catalogue sheet 7145) arranged for use with the switchboard 4 wire lines. For auto-working, dials a readjusted to transmit 10 p/s with 2:1 break/make pulse ratio, and have standard numbering (i.e. 1 to 0).
Height: 9 in (229mm)
Width: 23 in (587mm)
Depth: 15 in (387mm)
651b (29.5kg) net
Plessey Publication No. 7130 (1970)
Click here for an article from the Ericsson Bulletin
Click here for the GPO Switchboard No. 2/4
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