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 the instrument 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.
Instruments are also available with battery bells so that plans to suit almost any
requirement can be arranged. At each station allowed to call the exchange a separate
generator N8486 type is required (shown above).
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.
|N 20629||N 20630||N 20631|
|1K Key Unit||9K Key Unit Mounted||4K Key Unit|
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.
Overall dimensions 9.25 x 8.5 x 6 inches
Maximum weight 6 lb. 8 oz.
The telephones in the table below are complete with instruction tray fitment.
|Code No.||Description||G.P.O. No.|
|N8440A||Bakelite, magneto bell, no buttons||396LB|
|N8440H||Bakelite, magneto bell, no buttons, no tray|
|N8441A||Black Bakelite, magneto bell, 1K key unit and button|
|N8443D||Black Bakelite, magneto bell, three buttons (key unit to be stated)||394LB|
|N8444B||Black Bakelite, battery bell, three buttons||392LB|
|N8444B20||Black Bakelite, battery bell, three buttons (key unit to be stated)||392LB Mk2|
|N8445A||Black Bakelite, battery bell, no buttons or keys|
|N8446A||Black Bakelite, battery bell, 1K key unit and button|
|N8486A||Alnico Magneto generator in moulded case|
Dimensions 5.25 x 4.25 x 5 inches
Approximate weight 31 lb.
Note - Wall telephones for Plan Number Working can also be supplied.
Taken from the Ericsson catalogue, edition No. 49
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