GEC 10 Line PAX

GEC AEI TELECOMMUNICATIONS LIMITED
A Management Company of
The General Electric Company Limited of England

10 Line Private Automatic Exchange

STANDARD FEATURES
Maximum capacity
10 extension lines.

Connect circuits
Provision for one conversation at a time.

Numbering scheme
0 to 9.

Executive's priority
One selected executive can have a priority-button telephone enabling him to break into the existing conversation.

GENERAL
Mode of operation
Fully automatic operation with secrecy using uniselectors and relays.

Tones and ringing
Mains-supply derived ringing tone and current

Signalling
Required dial-pulse characteristics: 7 to 14 i.p.s., 2:1 break to make ratio.

Power supply
Built-in AC power unit: input, 100 to 120V or 200 to 250V 50 to 60 Hz single phase.

Line resistance
Line-loop resistance to exceed 300 ohms. Line-leakage resistance should be not less than 130k ohms.

Construction
Wired-in equipment on a wall-mounted frame and contained in a lift-off dust cover painted dark green.

Dimensions and Weight

Taken from a GEC-AEI brochure SLX8C - dated 1968

10 LINE
PRIVATE AUTOMATIC TELEPHONE EXCHANGE

This compact and completely self-contained telephone exchange provides secret automatic communication facilities for up to ten extensions. It is ideally suitable for small organisations, or as a separate auxiliary to the main telephone system in a large organisation. The single wall-mounting unit, finished in steel furniture green, incorporates all the automatic-switching equipment and an all-mains power unit.

The exchange has the following features:-

• Automatic connexion between extensions.

• Two-wire lines to each extension.

• One connecting link.

• Executive right-of-way for one extension.

• Operates from single-phase mains supply 50-60c/s, 100-110 or 200-250 volts.

• Dial tone and ringing tone returned to a caller.

• Extensions numbered from 0 to 9.

• The exchange is suitable for operation in either tropical or temperate climate.

Any extension user is connected to any other extension by dialling a single digit. When the connecting link is free, an extension hears dialling tone on lifting his receiver, and ringing tone when the wanted extension is being called. If there is no tone when an extension lifts his receiver, the connecting link is engaged.

One extension connected to the exchange can have an executive right-of-way facility. This extension instrument is fitted with a pushbutton, and to break-in to an established connexion the extension user presses the pushbutton. If neither of the answering parties is the one required, they are requested to replace their handsets ; the executive then dials the required number. In this way the head of a small organisation, or the leader of a group in a larger organisation, can talk to any member of his organisation at all times.

LINES AND TELEPHONES
Each telephone can be connected to the exchange unit by any insulated twin conductor having a loop resistance of less than 300 ohms and a line leak greater than 130,000 ohms. This latter condition means that bare open-wire lines should. not be used with this exchange. An extension with executive right-of-way facility must be connected to the exchange by two insulated twin conductors.

Recommended telephones for this exchange are the 'New Gecophone' described in Catalogue Leaflet STL16 and the "G.E.C. 1000" Telephone and the G.E.C. Muraphone "K" described in Catalogue Leaflet STL13. When the executive right-of-way facility is required, the executive telephone must be fitted with a pushbutton. The ringing current is derived from the mains at 50 or 60c/s, compared with the normal telephone exchange ringing current of 25c/s, therefore slight adjustment of the bell is required to give the most satisfactory ring.

The connexions to extension lines are by screw-type terminals, and the only tool required to install the exchange is a screwdriver. Each exchange is fitted with 10ft of 3-core flex to connect to the mains supply.

This compact, neat, inexpensive telephone exchange is easy to install, and available for quick delivery.

ORDERING INFORMATION

G.E.C. 10 LINE P.A.X.

Taken from the GEC Catalogue Leaflet No. PXL 06A (Date unknown but later than 1959)

Taken from the
GEC Journal (1959)

Private Automatic
Telephone Exchange for 10 Lines

This completely automatic exchange has been designed for small organizations or for use as a separate auxiliary system to the main telephone network in larger organisation provides secret communication between ten extensions using well-proven operational principles.

For more than two decades the G.E.C. 10-line �All relay� Private Automatic Exchange (P.A.X.) has been extremely popular with customers all over the world, and the demand for these small exchanges has far exceeded expectations.

Owing to the low operating voltage of 8-12 V d.c. and other factors, certain disadvantages were prevalent. These were the limited extension line range (20 ohm loop maximum), the use of non-standard telephone instruments with special d.c. ringers, and a 3-wire  connexion to each extension instrument. Consequently a new exchange employing well-proven operational principles has been developed to eliminate the disadvantages of the earlier �all relay� system. This new 10-line Private Automatic Exchange uses 2 uniselectors and 6 relays with a built-in all-mains power unit.


FACILITIES
Some of the facilities offered by the new exchange are:-

1. It is completely automatic and self-contained.
    
2. Secret communication between up to ten extensions can be obtained by dialling a single digit.
    
3. A two-wire line connexion is used.
    
4. Line range of up to 300 ohms loop resistance is provided. (Wire-to-wire insulation resistance must be greater than 130,000 ohms.)
    
5. Standard telephone instruments and dials are used.
    
6. Only one connecting link is employed.
    
7. Executive right-of-way (priority) is provided for one extension only, to enable the busy executive to break-in to an already established connexion. He may thus make use of the connecting link after instructing the other users to replace their handsets. The executive's telephone instrument is fitted with a press button for this purpose, and two extra wires are required for this extension line connexion.
    

8. The built-in power unit is designed for operation from a 100-110V or 200-250V, 50-60c/s single-phase a.c. supply, is compensated against + or - 6 per cent mains fluctuation and is adequately protected by fuses. A fully-smoothed output at 50 V d.c. is delivered to provide a noise-free current for the speech circuit, and to operate the switching apparatus. A separate winding on the mains transformer provides the ringing signal.

During an extensive field trial held at the G.E.C. Telephone Works in Coventry, a prototype unit was installed to test the adequacy of the single connecting link. The offices of the ten executives who required to keep in touch regularly were connected, and strict records made. It was found that the connecting link was engaged only once out of a tot2l of seventy-two cells made, and that this busy condition very soon cleared. Incidentally, when the field trial was completed the ten executives refused to give up the service
provided by the prototype exchange, and are still using it constantly.


CONSTRUCTION
Two important considerations in the design of the new equipment were that the unit had to be produced at very low cost, and the exchanges would probably be installed and maintained by people whose experience of telephone equipment would be extremely limited or even non-existent. Accordingly, the accent had to be simplicity. It was decided, therefore, to simulate the simplified "bread-board" type of construction known to the constructors of wireless sets in the early days of broadcasting. This type of construction would keep tooling down to a minimum, thus reducing costs.

The unit is designed for wall-mounting, and all the components are mounted on a steel base with draw-off cover. All the external connexions are by screw-type terminals, so that it is possible to install the unit using only a pen-knife and a screwdriver. The relay and uniselector mountings are hinged to give access to the wiring. A 3-core flexible lead is provided for connexion to a suitable mains power point. The unit measures 12in x 24in 7.5in and weighs approximately 38lb.


APPLICATION
The new P.A.X. is ideally suited to small organisations where the maximum number of extensions is never likely to exceed ten.

For the larger organizations a number of these exchanges could be used to provide small separate auxiliary systems to the main telephone network.  Another application is where a person raising a query on the main network may be asked to hold on while the answer is being sought using the auxiliary system.

The distinctive ringing signal of the new 10-line P.A.X. can never be confused with the signal of a larger exchange, making it possible to place the telephones of both main and auxiliary systems side by side on the desk.
 

ADDITIONAL PICTURES
Taken in 1959

10 PAX Tropicalised - Drawing 701060

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