Secretarial System Mk. VI
with Automatic or C.B. exchange lines

n1906.jpg (9866 bytes)This flexible 2-station system for principal and secretary ensures the busy executive freedom from the distraction of answering unimportant telephone calls and provides the following main facilities:
The secretary (Control Station) and principal (Terminal Station) have access to a joint exchange line, intercommunication facilities, and, if required, an exclusive extra exchange line at either or both stations, i.e. a maximum of three exchange lines.

Incoming calls on the joint line are answered by Control and extended to Terminal if necessary. Extended calls may be made secret or non-secret from Control by simple terminal-strap adjustment.

Outgoing calls on the joint line can be made from both stations.

A joint line call can be held and transferred if necessary by either station during an enquiry call.

Either station can effect operator recall by press button operation.

Exchange lines may connect to an auto or C.B. public exchange a PABX, PAX or PMBX. The exchange line loop resistance, including the telephone, can be up to 1000 ohms.

Lamp supervision is given as follows:-
(a) On both telephones by a green lamp if the joint line is engaged.
(b) On the disengaged telephone by a clear lamp if an exclusive line is engaged.

By means of an extend bell key on the Control telephone, incoming calls can be signalled at the Terminal station when Control is not manned.

Power Supplies
Power for the system is obtainable from any one of the following sources:
The local a.c. mains via a 6V battery eliminator (power unit).
Four 1.5V dry cells.
A local 50V power supply (e.g. from a PAX) via a retard/capacitor element in a buzzer unit.

Control telephone: one required.
Terminal telephone: one required.
50V Power feed and buzzer unit.
One unit is required for each exclusive line and is wall mounted near the telephone with which the line is associated. If there are no direct lines, one unit is required if the system is powered from a 50V supply.
Power unit (alternatively dry cells). Not required if system is powered from a 50V supply.

Cabling and Installation
The maximum distance permissible between stations is determined by the effective signalling distance, which allows a line resistance of 9 ohms. This is equivalent to about 200ft (61m) of 6.5 lb/mile (1.8kg/km) cable, but the distance can be greater with cable of heavier gauge.

Equipment Details
Telephone instruments Nl906D
These are fully tropical Plan-Etelphone type instruments, each with four press buttons and two lamps positioned as shown in the diagram overleaf. The appearance of the Control and Terminal telephones is identical, except for a lever switch below the dial on the Control telephone which is used to extend joint line incoming ringing to the Terminal station when the Control station is unattended. In this circumstance it can be arranged either for the Control bell to be switched off or left in circuit.

Stock instruments are ivory or two-tone grey; other colours in the Etelphone range could be supplied if required insufficient quantity. The components, all mounted on the base, are exposed by lifting off the telephone body which is secured to the base by two screws under the handset.

The instruments feature the normal Etelphone high-efficiency elements and handset. A plug-in automatic line regulator which controls transmission sensitivity over short lines is included; when not required it is inverted in the base jack. All springsets and the dial mechanism are protected by plastic covers; provision is also made to exclude dust and insects from the interior of the telephone.

Equipment Item   Code No.
Telephone (control or terminal)   N1906D
Buzzer unit   N24202A
Power unit   N23801B

The unit contains a retard/capacitor element to allow operation from a 50V supply, an a.c. buzzer
for direct line signals, and a screw terminal block for the connections.
The enclosure consists of a metal base and a moulded grey plastic cover secured by one screw.

Power unit
This is a battery eliminator incorporating transformer, choke, fuses and terminal block in a grey enamelled metal case. The smoothed output is 6V 1A d.c. and the input 100 to 125V in 5V steps, 200 to 250V in 10V steps.

Dry Cells (alternative to power unit)
These are usually purchased locally by customers.

Taken from the Plessey Telecommunication Publication No. 7147/1 ZH203/1.1 M/4.71

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Last revised: October 04, 2019