|C. B. Telephones
PLAN NUMBER WORKING
These telephones are for providing economically various extension schemes without the use of separate switches or switchboards.
They are arranged to accommodate key units having from one to nine spring sets of the make-before-break change-over type, i.e., "K" combination. The spring sets are operated by push buttons, and are illustrated overleaf.
For a simple extension or for recalling a P.B.X. operator the instrument N1366 type has a key unit with one set of K springs.
For other extension schemes the key units have a number of K spring sets, the standards being for 4 and 9 sets. The push buttons on a telephone with a 4K spring set operate respectively (left to right) 2K-1K-1K spring sets, while with a 9K set, 4K-1K-4K are operated.
Each contact spring is wired to a separate terminal so that the scheme in hand may be readily connected up.
On the 4K and 9K key units there is a mechanism which can be varied to
control the non-lock or locking of the two outer keys, the centre key being
non-locking. There is also supplied with each of these key units a T piece which
is fixed to the cradle lever when the extension plan necessitates the release of
a key on replacement of the micro-telephone.
The telephones are normally produced in black, but if specially ordered, they can be supplied in Chinese red, ivory or jade green. They can also be obtained without the instruction tray and directory pad fitment.
For telephones with two or three push buttons the key unit required must be stated.
In the case of plans requiring only two push buttons, chromium finished dummies can be supplied for the third hole.
The terminal blocks, cords and labels vary according to the plan required, so that full details regarding the scheme to be operated should be supplied when ordering.
Circuit diagrams of various plans can be supplied on request.
Above telephones were also supplied to GEC, A.T & E, S.T & C and BR (WR)
See N1003 for automatic types
Note - Wall telephones for Plan Number working can also be supplied.
Last revised: October 01, 2019