(British Trade Mark Application No. 855077163)

The development of the 'Multiphone' has, among other applications, virtually enabled the facilities of a P.A.B.X. having up to 4 exchange lines and 10 internal intercom stations to be provided in a multi-button instrument no larger than the Etelphone, without employing a manual switchboard. It may be a self-contained P.A.B.X., or auxiliary to an existing P.A.B.X. or P.A.X.

The total equipment consists of the requisite number of station telephones, a common central control unit of small dimensions, separate exchange line ringers, and protectors for the external lines.

The equipment has tropical finish. All connecting wires are insulated with p.v.c. which is moisture-proof, fire resistant and not subject to fungoid growth or attack by insects.

Features of the system are:

(1) Economic cost. In addition to the saving effected by avoiding the use of a manual switchboard, the station telephones and control unit can be equipped for only 2 + 1 0 instead of 4 + 1 0 lines if required.

(2) Reliability by virtue of the low fault-liability of the simple switching mechanisms.

(3) Simplicity of Installation. Cabling is straightforward and screw terminals are provided for all cable connections.

(4) Convenience for Operating. Calls between stations are made by dialling single-digit codes; lamp signals are provided for incoming calls, held calls and calls in progress.

n1644.jpg (13328 bytes)Type N1644
Station Telephone for the 4+10 line system with exclusion feature shown right.

Exchange line loop resistance: 1000 ohms maximum. Loop resistance between individual stations and the central control unit:

35 ohms maximum, i.e. equivalent to 220 yards (201 m.) of 61 lb./mile cable.

The 24 volts d.c. supply for the system and 6 volts a.c. for the lamp signals are obtained from a battery eliminator in the control

(a) All stations can originate, answer, hold or transfer exchange calls.

(b) Any station can hold an exchange line and make an information call to another station; the local conversation is not overheard by the exchange subscriber.

(c) Series exchange secrecy on one exchange line (by means of an exclusion button) at selected stations.

(d) Secret or non-secret intercom (by strap adjustment) over the connecting link, with selective dialling between stations.

(e) Audible and lamp signalling of incoming calls.

(f) Lamp supervision of held calls and calls in progress.

(g) Exchange service is maintained in the event of failure of the mains supply.

The exclusion feature (Facility C) is optional. The diagram shows the station telephone push-button arrangements for each of the four possible systems. In all other respects the appearance of the telephone is the same.  Buttons are individual or twin type.

Button 1 to 4 (locking) Press to connect to exchange line.
Button H (non-locking) Press to hold exchange call.
Button I (locking) Press to connect to intercom link.
Button X (locking) Press for secrecy on the allocated exclusive exchange line.
Button O (non-locking) Press to release X button if transferring exclusive exchange call.

multipho.jpg (40965 bytes)Right
Rear view of typical Control Unit showing power pack on left, with ringing current generator below and screw terminal blocks for cable and jumper connections behind the relay sets.


These are two-tone grey table instruments moulded in high-impact-resistant plastic; their general construction is as described for the auto Etelphone in Catalogue Section 1.

N1643 is equipped for up to 2+10 lines, and N1644 for systems with 3 or 4 exchange lines and up to 10 intercom stations.

Push buttons are provided as shown in the diagram. The exclusion feature can be added to a telephone not having the facility, as the appropriate switch springs are included in all instruments.

Incoming intercom calls are signalled by the telephone ringer and also by the lamp at the top left of the dial, which winks rapidly. When the intercom link is occupied, the lamp glows steadily at all stations.

A supervisory lamp is associated with each exchange line button. There are three signals: (1) a steady glow (line busy), (2) a rapid wink (incoming call), (3) a slow wink (line held). Incoming exchange calls are also signalled by the separate ringer N3121A.

EXCHANGE RINGER (N3121A)This is a compact moulded grey-plastic unit containing the ringer and screw terminals. At least one ringer per exchange line is necessary. They are installed on a wall or partition near the station (or stations) designated for answering incoming exchange calls. Extension bells are supplied if required, the signal received at the first station being repeated to the other answering station(s) by a transistor ringing-generator in the control unit.

CONTROL UNIT (N23989 or N23990)

Control unit N23989 for systems having up to 2+10 lines, or N23990 for up to 4+10 lines, is centrally situated, and may be installed on a table or wall.

The apparatus is frame mounted on the base of a grey-enamelled metal box having a pull-off cover, the same box being used for both of the two equipment’s.

There is accommodation for 7 relay sets in four types, a transistor ringing-generator, and a battery eliminator suitable for mains inputs of 110 volts to 250 volts, 50/60 c/s and having outputs of 24 volts d.c. and 6 volts a.c. At the back of each relay set is a screw terminal block to which the cables are connected. The blocks are interconnected by jumpers to enable connections to be easily arranged to suit the particular system and to simplify extension if required.

The power connection is a 3-point reversible shrouded plug which interlocks with the cover.

Installation is simple and normally undertaken by the customer.

All lines terminate at the control unit. For each exchange line, 6 conductors are series multiple-connected via the desk terminal blocks of the station telephones.

For internal communication, each station requires 5 leads directly connected to the control unit; 6 wire cable is normally used.

Cable is cream p.v.c. insulated.


Type No.   Description   Provision   Dimensions in. mm.   Weight lb. kg.
N1643 2+10 Telephone As required (max. 10) 11 x 9.25 x 5.5 (279 x 235 x 140)   4 (1.82)
N1644 4+10 Telephone As required (max. 10) 11 x 9.25 x 5.5 (279 x 235 x 140)   4 (1.82)
N3121A Exchange Bell 1 per exch. line (min.) 6 x 3.5 x 2 (152 x 92 x 51)   1.25 (0.5 9)
N23989 2+10 Control Unit 1 per system 30 x 13.5 x 11.25 (762 x 343 x 286) 70 (31.78)
N23990 4+10 Control Unit 1 per system 30 x 13.5 x 11.25 (762 x 343 x 286) 82 (37.23)
N6543 Line Protector 1 per external line pair 5.25 x 3.25 x 3.5 (133 x 83 x 89) 1.1 (0.51)

Taken from the Ericsson Catalogue No. 60

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Last revised: October 01, 2019