|PRIVATE MANUAL BRANCH EXCHANGES
with Automatic, CB, or Magneto exchange lines
This switchboard may be used either as a private exchange with magneto extension lines only, or as a private branch exchange connected to an automatic, C.B. or magneto public exchange. Twenty automatic, C.B. or magneto exchange lines can be accommodated; magneto exchange lines may be either additional lines or converted extension lines. Extension capacity is 100 with 17 cord circuits, but stock units are available with 50 or 70, extension lines, 10 or 12 cord circuits and wired but not equipped for exchange lines.
For installations from 100 up to 200 extensions, two units may be bolted together to form a two position, non-multiple switchboard. When up to the maximum of 400 extensions is required, four units, with provision for multiple working, can be similarly installed. Where two or more positions are installed en suite, each is equipped with longer connecting cords and double pulley weights.
For magneto working, one speak/ring key per cord circuit together with a common ring back key are fitted. When auto exchange lines are to be connected, additional equipment includes one dial key per line and a dial.
The face panel has indicators arranged in two groups on either side of the jack strips, and includes provision for equipment for other facilities as required. In addition, the jack panel has capacity for up to 100 multiple jacks for use when switchboards are multipled together. The key shelf is arranged with supervisory indicators and switching keys for cord circuits and miscellaneous facilities. Internal equipment is positioned and mounted for maximum accessibility. Incoming cables enter via covered apertures in the open constructed plinth, and terminate on soldered terminal fields positioned at the bottom of the unit.
For convenience of handling (e.g. during installation) the hinged key shelf can be raised and its apron lowered to reduce the depth by 8in (216mm). The weight of stock units varies depending upon the extension-line capacity.
Operating equipment, supplied as standard, includes a lightweight plug-in handset with
capsule receiver and a manually operated ringing-current generator. Alternative equipment,
available in lieu of or in addition to, is a lightweight plug-in headset and a transistor
ringing unit powered from a separate 6V source. On switchboards with auto exchange-line
connection, a dial adjusted to transmit 10 pps with 2:1 break/make pulse ratio and with
standard numbering, i.e. 1 to 0, is supplied as standard. Alternatively, a dial with any
required adjustment and numbering can be provided if required.
Plessey Publication No. 7134 (1970)
Last revised: October 12, 2019