GEC 50 LINE
NON-EXTENSIBLE PAX

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

50 Line Private Automatic Exchange
PX1450

STANDARD FEATURES
Maximum capacity
50 extension lines.

Connect circuits
Provision for 6 simultaneous conversations.

Numbering scheme
Within the range 20 to 75.

Executive's priority
Selected executives can break into an existing conversation: either the executive operates a pushbutton on the telephone when he hears engaged tone, or the break-in can be effected automatically.

OPTIONAL FEATURES
Tie lines
Up to 3 on one route only.

Conference
Up to 10 designated extensions can be connected together via a special circuit.

Fire alarm
Various procedures are available to suit individual requirements and local fire regulations.

Staff location
Staff absent from their offices may be called by dialling a special locating number followed by a personal code, to operate lamps or bells.

Secretary service
A secretarial switching telephone enables secretaries to filter calls to an executive.

Public exchange lines
Up to 4, after the addition of a special attendant's cabinet.

GENERAL
Mode of operation
Fully automatic using uniselectors and relays.  All conversations secret from each other.

Tones and ringing
Electronic tone generators provide dial tone, ring tone and current, and busy tone.

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

Alarms
Audible indication of blown fuse.

Power unit
AC power unit: input 100 to 120v or 200 to 250v, 50 to 60 Hz single phase; output, 26v d.c. 5A.
or
Battery: 26v 32AH; with float charger, input as for AC power unit; output 26v d.c. 3A.

Line loop resistance
Not to exceed 250 ohms.

Construction
Wired-in equipment mounted on a steel framework and contained in a steel cabinet (painted dark green) with lift-off dust-proof covers front and rear.

Dimensions and Weight

Catalogue Leaflet dated 1968

GEC 50 LINE
PRIVATE AUTOMATIC TELEPHONE EXCHANGE

The G.E.C. 50 Line non-extensible private automatic telephone exchange provides rapid and secret intercommunication by the simple dialling of two digits.   It is invaluable in large and small businesses to provide automatic interconnexion between members of the staff.   The exchange is essentially designed for internal communication only but by means of the G.E.C. P.A.X. Attendant's Cabinet, it can be connected to up to three lines from a public exchange.   It employs the same apparatus that has been standardised for large public exchanges by many Overseas Governments and the British Post Office.

The exchange can be supplied with Initial equipment for as few as 25 lines: equipment can be added later to bring the total to 50 lines.   Through circuits for conversation are established by connecting links, of which four, five or six may be fitted as desired, to permit the corresponding number of simultaneous conversations.

The exchange is contained in a floor-mounting.   dust-proof, sheet-steel cabinet fitted with lift-off doors front and rear to give easy access to the apparatus for maintenance.   The cabinet is finished in dark green.

A complete system consists of the exchange unit, the telephones, the connexions from the telephones to the exchange, a G.E.C. mains unit or a battery and float-charger, and possibly a distribution frame and protection apparatus.

STANDARD FEATURES

FULL INTERCOMMUNICATION
Every extension user can dial any other; a maximum of six simultaneous conversations can be held.

NO OPERATOR REQUIRED
The operation of the system is fully automatic and needs no manual supervision.

SECRECY
Absolute secrecy of each conversation is ensured by the use of circuits and apparatus deigned to eliminate overhearing.

EXECUTIVE RIGHT-OF-WAY
By means of this facility certain executives can exercise priority and get through to the wanted extension even though that extension may he already engaged.   A push-button, provided on the telephone instrument, is depressed when busy tone is received.   The executive is then immediately connected to the wanted party.   Alternatively, the push-button can he dispensed with if required, by means of permanent strapping on terminals at the exchange, whereby the executive never receives busy tone and is always immediately connected to the wanted party.

CONFERENCE LINES
These enable conferences to take place by telephone whilst the participants remain at their desks.   Two types of conference facility are available, one for a number of participants limited by the number of links available and the other without such limit.   The limited conference facility entails the use of one connecting link per participant which may result in blockage of calls through the exchange until the conference has ended.   This facility is the cheaper of the two.   The unlimited conference facility provides for conferences with no limit to the number of participants as no links are employed.   (Additional apparatus is mounted externally to the cabinet housing the automatic unit).   A conference can be called by any person with the unlimited conference facility.   Please state the type required and the number of participants and conveners.

STAFF LOCATION
Officials absent from their offices can be called by a system of lamps or bells.   A special "Locating" number is dialled from any telephone followed by digits in a personal code.   Please state whether a visual or audible call is required, how many codes are needed, and the number of calling stations likely to be used.

FIRE ALARM SERVICE
The exchange can be arranged to give a fire alarm service that meets the particular requirement of any organisation.   For instance, by dialling a "Fire" number from any telephone, alarm signals can be made to sound at required points.   Please state the facilities required, the calling system to be adopted and number of fire points.   It is wise first to consult the local fire regulations.

PUBLIC EXCHANGE SERVICE
Although the exchange is intended for internal intercommunication in a private network, it can be associated with up to three lines to the main public telephone exchange by means of a P.A.X. Attendant's Cabinet.   The extension user having this Cabinet on his or her desk in conjunction with the usual telephone instrument acts as an operator as and when necessary to make and receive calls over the lines to the local public exchange and to switch the lines through the P.A.X. to any extension.

Please state the number of exchange lines required, the type of public exchange into which the board must work and the line loop resistance of the exchange lines.   This information should be obtained from the local telephone Administration.

TIE-LINE SERVICE
The use of an internal service is not necessarily confined to any one building ; two or more G.E.C. P.A.X. units in buildings several miles apart can be linked by tie-lines to permit intercommunication between extensions in all the buildings.

A maximum of three such tie-lines can be used with this 50-line exchange.   Please state the type of P.A.X. into which the tie-line must work and the line loop resistance of the tie-lines themselves.   Should an existing P.A.X. be of other than G.E.C. manufacture, its circuit drawings should be provided when an enquiry is made.

SECRETARY'S SERVICE
The secretary is provided with a G.E.C. Switching Telephone whereby she can filter all incoming calls to the executive, who is provided with a G.E.C. Extension Telephone.   Direct connexion between executive and secretary is also available without the call being routed through the P.A.X. (See Leaflet MTL2.)

TELEPHONE INSTRUMENTS
Any automatic telephone having a dial impulse speed of between 7 and 14 impulses per second, with a ratio of 2 to 1 break to make, is suitable for use with this exchange.
Recommended telephones are the "New Gecophone," the " G.E.C. 1000" Telephone and the G.E.C. Muraphone "K", described in leaflets STL 16 and STL 13.

G.E.C. Loudspeaking Telephones have been designed especially for this P.A.X., and are described in leaflet STL 15.   The user has complete freedom of movement about the room whilst making the call.

For extensions having executive right-of-way the telephone instruments are fitted with a special pushbutton.

LINE WIRES
Any insulated twisted pair, or open-wire conductor for external lines, may be used.   Lines should be suitably protected if exposed to the risk of damp or mechanical damage.   Line loop resistance (the resistance of two wires in series) should not exceed 250 ohms.

The following table gives examples of maximum lengths for various line-wire conductors.
 

Each extension requires a two-wire connexion to the exchange unit, unless the extension is provided with executive right-of-way facilities, when the requirement is a three-wire connexion to the exchange, with an earth (ground) connexion from the telephone.

DISTRIBUTION
The simplest method of connecting the telephone instruments to the exchange is to use a separate line-wire pair for each telephone.   A saving in line-wires, however, may often be effected by running a multi-core cable, 50-pair, 25-pair or 12-pair, from the exchange to a junction-box, or boxes, so situated that only short lengths of separate line-wires are then required to connect the telephones to the junction-box.

Distribution frames, on which the exchange lines are terminated and to which the telephones are wired, are supplied if ordered.   The use of a distribution frame simplifies alterations to numbering schemes and line testing and also provides protection against high voltages or heavy currents that may accidentally be introduced from extraneous sources.
As the distribution scheme must vary according to the geographical layout encountered, please state whether or not cable and junction-boxes are to be supplied; if they are, a dimensioned sketch of the disposition of the exchange unit and telephones should be included.

PROTECTION
Provided the line-wires connecting each telephone to the exchange are all run inside a building, no form of protection against lightning is required.   Should, however, any open-wire lines be run outside the building, line protection apparatus must be employed on each such line.   Please state the number of lines to be protected: suitable protection apparatus will then be provided.

POWER SUPPLIES
A 26-volt DC power supply is required for the operation of this exchange and may be obtained from an AC mains unit or storage batteries.   The specially-designed G.E.C. mains unit is recommended except where the mains supply is unreliable, when storage batteries may be preferable.   If storage batteries are employed a float charge system should be used.   The recommended capacity for the battery is 30 ampere hours at the 10-hour rate of discharge.   A battery and float-charger are supplied if ordered.

ORDERING INFORMATION

G.E.C. 50 LINE NON-EXTENSIBLE P.A.B.X.

SPECIAL FACILITIES
If any of the special facilities described in this leaflet are required, please quote details after the catalogue number of the exchange unit.

POWER SUPPLY
Power Supply Unit for operation from a 100/120 or 200/250 volt 50/60c/s single-phase mains supply having an output of 24/28 volts DC.
Catalogue Number:  SU 3201
Dimensions: 17 x l21 x 9 ins; 43 x 32 x 23 cms
Approx. Weight: 38 lb; 17 kgs

Automatic Float Battery Charger for operation from a 100/120 or 200/250 volts 50/60c/s single-phase mains supply having an output of 24/28 volts, 0-3 amps DC, and suitable for charging a 12-cell, lead-acid battery.
Catalogue Number:  SU 4201
Dimensions: 17 x 122 x 9 ins; 43 x 32 x 23 cms
Approx. Weight: 42 lb; 19 kgs

12-cell, nominal voltage 26, lead-acid storage battery, less stand, acid and accessories, capacity 30 ampere-hours at 10-hour rate of discharge.
Catalogue Number:  BA 1101

Details of a lead-acid battery of 20 ampere-hour capacity will be supplied on request.

P.A.X Attendant Cabinet for up to three of four exchange lines
Catalogue Number:  PX 4201

Taken from the GEC Catalogue Leaflet No. PXL 03D (Date unknown but later than 1959)

GEC 50 LINE 6 LINK PRIVATE AUTOMATIC TELEPHONE EXCHANGE
For up to six simultaneous conversations

The G.E.C. 50-line non-extensible private automatic telephone exchange provides rapid and secret intercommunication by the simple dialling of two digits.   It is invaluable in large and small businesses to provide automatic interconnexion between members of the staff.   The exchange is essentially designed for internal communication only but by means of the G.E.C. P.A.X Attendant's Cabinet, it can he connected to up to three lines from a public exchange.   It employs the same apparatus that has been standardised for large public exchanges by many Overseas Governments and the British Post Office.

The exchange can he supplied with initial equipment for as few as 25 lines; equipment can be added later to bring the total to 50 lines.   Through circuits for conversation are
established by connecting links of which four, five or six may be fitted as desired, to permit the corresponding number of simultaneous conversations.

The exchange is contained in a floor-mounting, dust-proof.   sheet-steel cabinet fitted with lift-off doors front and rear, to provide easy access to the wiring and apparatus.   The cabinet is finished furniture green in accordance with BSS.279; other finishes can be supplied to meet special requirements.   In addition, the exchange can be supplied in a floor-mounting dust-proof cabinet of matt-polished hardwood, fitted with a glass-panelled front door and lift-off rear door.

A complete system consists of the exchange unit, the telephones, the connexions from the telephones to the exchange, a G.E.C. mains unit or a battery and float-charger, and possibly a distribution frame and protection apparatus.

FACILITIES
The facilities provided by the exchange differ in no respect from those of the 50-line exchange described in Catalogue Leaflet PXL 3B under the following headings:

• FULL INTERCOMMUNICATION
• TELEPHONE INSTRUMENTS
• NO OPERATOR REQUIRED
• LINE WIRES
• SECRECY
• DISTRIBUTION
• EXECUTIVE RIGHT-OF-WAY
• PROTECTION POWER SUPPLIES

The following optional features are provided if ordered, as described in Catalogue Leaflet PXL 3B:

• CONFERENCE LINES
• PUBLIC EXCHANGE SERVICE
• STAFF LOCATION
• TIE-LINE SERVICE
• FIRE ALARM SERVICE
• SECRETARY'S SERVICE

ORDERING INFORMATION

G.E.C. 50 LINE
NON-EXTENSIBLE P.A.B.X.

Taken from the GEC Catalogue Leaflet No. PXL 05A

GEC 50 LINE
PRIVATE AUTOMATIC TELEPHONE EXCHANGE

Brochure is the same as PXL 05B

ORDERING INFORMATION

G.E.C. 50 LINE NON-EXTENSIBLE P.A.B.X.

SPECIAL FACILITIES
If any of the special facilities described in this leaflet are required, please quote details after the catalogue number of the exchange unit.

POWER SUPPLY
Power Supply Unit for operation from a 100/120 or 200/250 volt 50/60c/s single-phase mains supply having an output of 24/28 volts 0-5 amps DC.
Catalogue Number:  SU 3202
Dimensions: 17 x l21 x 9 ins; 43 x 32 x 23 cms
Approx. Weight: 38 lb; 17 kgs

Automatic Float Battery Charger for operation from a 100/120 or 200/250 volts 50/60c/s single-phase mains supply having an output of 24/28 volts, 0-3 amps DC, and suitable for charging a 12-cell, lead-acid battery.
Catalogue Number:  SU 4201
Dimensions: 17 x 122 x 9 ins; 43 x 32 x 23 cms
Approx. Weight: 42 lb; 19 kgs

12-cell, nominal voltage 26, lead-acid storage battery, less stand, acid and accessories, capacity 30 ampere-hours at 10-hour rate of discharge.
Catalogue Number:  BA 1101

Details of a lead-acid battery of 20 ampere-hour capacity will be supplied on request.

Taken from the GEC Catalogue Leaflet No. PXL 03D (Date unknown but later than 1969)

Last revised: November 30, 2021