gec.gif (1164 bytes)GEC  PABX 4+24 & 8+49


GEC Telecommunications Limited
A Management Company of The General Electric Company limited of England

4 + 24 line, extensible to 16 + 48 line Private Automatic Branch Exchange

STANDARD FEATURES
Maximum capacity

Choice of 4 public-exchange lines and 24 extension lines, or
12 public-exchange lines and 23 extension lines
or
8 public-exchange lines and 49 extension lines
or
16 public-exchange lines and 48 extension lines.

Individual extensions can be prevented from dialling public exchange calls.

Incoming
Through operator's switchboard.

Enquiry and transfer
Telephones with a pushbutton can be supplied to all or selected extensions to enable a public exchange call to be held while the user calls another extension with an enquiry.  When the enquiry is complete, the original extension returns to the public-exchange call, or can transfer it to another extension or to the operator.

Night service
Incoming public-exchange calls can be answered from any extension by dialling '8'; alternatively, the feature can be restricted to one extension only.  Calls can then be transferred to other extensions by the enquiry and transfer method.

Trunk offer
The operator can offer a public-exchange call to an extension already engaged.

OPTIONAL FEATURES
Tie lines

Normally up to 2 for 24 extension lines and up to 4 for 49 extension lines, on one route only, at the expense of public-exchange circuits.

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

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

Route restriction
Individual extensions may be permitted to dial local but not long-distance calls.

Mains-fail protection
Public exchange lines can be automatically connected to designated extensions in the event of an AC mains supply failure.

GENERAL
Mode of operation
Fully automatic operation using 2-motion selectors, uniselectors and relays.  All conversations secret from each other.

Tones and ringing
All-electronic tone generator provides dial tone, ring tone and current, busy tone, number-unobtainable tone and operator intrusion tone.

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

Alarms
Lamp indication at switchboard.
Urgent: release alarm, ring fail and blown fuse.
Deferred: failure to replace receiver (PG condition).

Power unit
AC power unit: input, 100 to 120V or 200 to 250V, 50 to 60 Hz single phase; 50V d.c. output 5A for 4 + 24 line, 10A for 12 + 23 line and 8 + 49 line, 20A for 16 + 48 line.
or
Battery: 50V; with float charger, input as for AC power unit, 50V d.c.

Line-loop resistance
Not to exceed 900 ohms.

Construction
Switching equipment: Plug-in and wired-in units on a steel framework in a floor-mounting steel cabinet (painted grey) with lift-off dust-proof panels front and rear.
Switchboard: cream and green desk-mounting console.

Dimensions and weight
4 + 24 line exchange = 1 module; 12 + 23 line exchange = 2 modules;
8 + 49 line exchange = 2 modules; 16 + 48 line exchange = 3 modules

    Height    Width    Depth    Weight
Line switching equipment module    2090mm (82in)    600mm (24in)    510mm (20in)    210kg (460lb)
Switchboard    115mm (4.5in)    325mm (13in)    230mm (9in)    7 kg (15lb)
AC mains unit (4 + 24 exchange)    530mm (21in)    390mm (15in)    230mm (9in)    28kg (62lb)
AC mains unit (others)    1220mm (48in)    480mm (19in)    390mm (15in)    108kg (238lb)
Float charger    530mm (21in)    390mm (15in)    230mm (9in)    35kg (76lb)

Catalogue Leaflet dated 1972

 


4 + 24/8 + 49 LINE PRIVATE AUTOMATIC BRANCH EXCHANGE

The G.E.C. 4 + 24/8 + 49-line private automatic branch exchange has an ultimate capacity of eight lines to the public exchange and forty-nine extensions.  The exchange is supplied in two units; the first unit is a complete exchange in itself having a capacity of four lines to the public exchange and twenty-four extensions, and the second unit is added when required, to bring the exchange up to its ultimate capacity.  One extension calls another by dialling two digits.  An extension obtains direct access to the public exchange by dialling "9".  This direct access is given to selected extensions and withheld, if desired, from others.  All extensions can gain access to the public exchange via the P.A.B.X. attendant by dialling "0".

An incoming call from the public exchange is signalled on an attendant's cabinet, and extended to the wanted party by the attendant.  Up to eight extension-to-extension conversations can be held simultaneously when two units are installed, and up to four for the single unit.  When an extension makes a call to the public exchange, the connecting link in the P.A.B.X. is in use only while the connexion to the exchange line is being established.  The link is then released for use by the next caller.

The P.A.B.X. will work to public automatic and C.B. manual exchanges.  If the public exchange is of the magneto or C.B.S. type, an auxiliary unit is supplied to effect the necessary signalling.

Font View (Doors closed) Rear View (Doors opened)

Each automatic exchange is housed in a dust-proof sheet-steel cabinet, 6' 10" x 1' 1l" x 1' 8" (209 cms x 60 cms x 50.5 cms).  Each cabinet has two lift-off doors at front and rear to allow easy access to the equipment for maintenance purposes.  The bars supporting these doors can also be easily removed when required.

The cordless attendant's cabinet has been re-styled to be in keeping with modern office furnishings.  This is illustrated on the front of the leaflet.  Cabinets having green end panels can be supplied instead of the red-panels when required.  The size of the cabinet is 1' 2" x 11.5" x 5" (37 x 29 x 12.7 cms).

The complete P.A.B.X. system consists of the automatic unit, attendant's cabinet, telephones, magneto extension bells, when required, for night-service working, line wires from the unit to the telephones, power supply equipment, and protection apparatus for all lines that run outside buildings.  A distribution frame on which all lines are terminated, and all protection apparatus mounted, is recommended for use with the 8 + 49 line exchange, but is not necessary for the 4 + 24-line exchange

STANDARD FEATURES
FULL INTERCOMMUNICATION

Any extension user is connected to any other extension by dialling the appropriate number.  The extensions are normally numbered from 21 to 69, or from 21 to 44 with the 4 + 24-line P.A.B.X.

OUTGOING CALLS
Direct access to the public exchange is obtained by dialling the single digit "9".  If the public exchange is automatic, the caller then dials the number of the required subscriber ; if the exchange is manual, the call is completed by the public exchange operator.  Certain extensions may be barred from this facility, if desired, by a simple adjustment to the strapping in the automatic unit.

Alternatively, calls to the public exchange can be made via the attendant's cabinet, access to which is obtained by dialling the single digit "0".  On dialling "0", an extension is connected to one of the two "0" level calling lamps on the attendant's cabinet, the lamp flashing to indicate the call.  The attendant answers the call by operating a lever-type key associated with the calling lamp.  The extension may now replace his handset, and is recalled by the attendant when the call matures.  All extensions may obtain calls to the public exchange via the attendant, and equipment is provided for two simultaneous "0"-level calls.  If both the "0" level lines to the attendant's cabinet are in use, a third party dialling "0" may hold on.  He would then be connected to the attendant automatically when one of the lines became free.

INCOMING CALLS
An incoming call from the public exchange causes an associated lamp on the attendant's cabinet to flash.  The attendant answers the call by operating the key corresponding to the flashing lamp, and extends the caller to the required extension by key-calling the extension number on a strip of miniature lever-type digit keys.  If the called extension is free, the exchange lamp on the cabinet glows continuously until the call is answered, when the lamp is extinguished.  If the called extension is engaged on an internal call, the exchange line lamp flashes (at a different frequency to the calling signal) and the attendant can operate the trunk-offering key and offer the incoming exchange call.

CALL-BACK AND AUTOMATIC TRANSFER
An extension engaged on a call over an exchange line may hold the call (by pressing a button on his telephone), while he calls another extension.  At the end of the conversation with the second extension, he resumes his conversation on the exchange line by depressing the button again.  Alternatively, if he wishes, he may transfer the exchange line to the other extension merely by replacing his own handset.

Any telephone may receive a transferred call; if it is fitted with a pushbutton the user may transfer the call again.

By pressing the pushbutton twice in succession, an extension can recall the attendant by causing the associated exchange-line lamp to flash.

NIGHT SERVICE
Night-service working is established by the operation of the night-service key on the attendant's cabinet.  Two methods of operation may be used, the required one being selected by the simple adjustment of the strapping on a terminal block.

In the first scheme, one particular extension is selected to answer all the incoming calls at night.  An incoming call rings this extension's telephone bell, and to answer the call, the extension lifts the handset and dials "8".

In the alternative scheme, an incoming call at night rings separate bells at different selected places.  The call is answered at any extension by lifting the handset and dialling "8".  For this arrangement the number of bells required should be specified when ordering.

RINGING AND TONES
Dial and ringing tones, together with ringing current are generated by means of vibrating generators and NU (number unobtainable) and busy tones by a valve oscillator, fitted in the automatic unit.

ALARMS
Two alarm lamps are fitted on the attendant's cabinet, one for deferred alarms and the other for urgent alarms.  The deferred-alarm lamp lights to indicate a P.G. (permanent glow) condition within 30 to 60 seconds of the condition being set up.  The urgent-alarm lamp lights to indicate one of the following : release alarm, ringing-fail alarm, or fuse alarm.  An audible alarm with cut-off key is associated with the alarm lamps.

ADDITIONAL FEATURES
The standard P.A.B.X. unit and attendant's cabinet are wired to allow several additional features to be provided either at the time of installation of the exchange or at a later date.  The additional features include:-

TIE LINES
Tie lines can be provided between the P.A.B.X. and other private telephone exchanges either in adjacent buildings or in buildings up to several miles apart, to permit intercommunication between extensions in each of these communities.  The number of tie lines permissible depends on the size of the exchange.
Please state the type of private exchange to which interconnexion is desired and the line loop resistance of the proposed tie lines.  Should the exchange to which connexion is desired be of other than G.E.C. manufacture, its circuit drawings should be provided with the enquiry.

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 (or the attendant's cabinet), followed by digits in a personal code.  Please state whether a visible or audible call is required, how many codes are needed, and the number of calling stations likely to be used.

CONFERENCE LINES
These enable conferences to take place by telephone while the participants remain at their desks.  No links are employed by the conference ; each participant's telephone is fitted with a pushbutton and connected to the exchange by an additional line pair.  The conference is opened by each participant being individually called by the convener; each then presses the pushbutton on his instrument to give direct connexion to the conference circuit at the exchange.  Please state the number of participants.

MANUAL EXTENSIONS
Four lines can be connected direct to the attendant's cabinet.  These are additional to the 49 automatic extensions and are for those extensions who desire the attendant to establish their calls, whether internal or external.  The telephones of these extensions are not fitted with a dial, and when the caller lifts his handset, a lamp flashes on the cabinet.  The attendant answers, establishes the connexion, and then rings back to the caller.

SECRETARY'S SERVICE
A secretary may be provided with a G.E.C. switching telephone so that all calls to an executive may be filtered.  The executive would have a G.E.C. Extension telephone.  Calls between executive and secretary are not routed through the P.A.B.X.  Full details of this service are given in the G.E.C. Leaflet STL.17.

EQUIPMENT
AUTOMATIC UNIT

The automatic switching apparatus is mounted in one or two steel cubicles, which have lift-off doors front and rear, to give easy access to the equipment.  Easily-removable metal covers protect the relays against dust and damage.  All the apparatus is the same as that standardised for large public exchanges in many-parts of the world and includes the G.E.C. SE50 two-motion selector.  Throughout, the unit and apparatus is designed to give ease of maintenance.

ATTENDANT'S CABINET
The attendant's cabinet has an attractive, modern appearance.  It is very compact and stands on a desk or table.  All the components are mounted on a steel framework over which a plastic cover is fitted.  The cover can be either red or green, both colours providing a pleasing contrast to the biscuit colour of the facia panel.  All keys fitted are the latest miniature lever type.
When not in use, the attendant's handset is accommodated in a cradle fitted at the rear of the switchboard.
Calls to the attendant are signalled on any of fourteen calling lamps, of which eight are associated with lines from the public exchange, four with the P.A.B.X. manual extensions and two with calls from the automatic extensions.  The call is answered by the simple operation of the key associated with the flashing lamp.
A strip of keys provides key-calling facilities to allow calls to be rapidly connected to wanted extensions.  The attendant's cabinet is also equipped with a dial for use on calls to the public exchange, the that being switched out of circuit when not in use.
Other keys in the cabinet provide for supervisory facilities, night service, extension of alarms from the automatic unit, code call and an additional key and lamp for any special service that may be required, e.g. dictation.

POWER SUPPLY
The exchange operates on a 50-volt DC power supply.  When the mains supply is AC, the DC supply may be obtained from a mains unit or from storage batteries.  A G.E.C. mains unit is recommended except where the mains supply is unreliable, when a storage battery is necessary to maintain continuity of service.  When a battery is 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.  Further information regarding the float chargers may be obtained on request.

Where the mains supply is DC, a rheostat should be used to step the mains voltage down to the voltage required to charge the batteries.  With this arrangement a charge-discharge system must be used so that the battery connected to the mains is isolated from the exchange.

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 Muraphone "K", described in G.E.C. Leaflets STL16 and STL13.
A telephone fitted with a pushbutton is supplied for any extension requiring the call-back and automatic transfer facility.  When ordering please state the number of telephones required with pushbuttons fitted.

LINE WIRES
Any insulated twin conductor, suitably protected if exposed to risk of damp or mechanical damage may be used to connect the telephones to the exchange provided the line loop resistance does not exceed 900 ohms.  A third wire must be connected from the telephones of extensions having the call-back and automatic-transfer facility to a nearby earth point.  If there is no convenient earth point, the third wire must be run to the exchange unit.  The following table gives examples of maximum lengths for various line wire conductors.

Size of Copper Conductors Maximum Permissible Length of Cable Pair
lb/mile AWG (B & S) SWG mm Diam. Yards Metres
4 26 27 0.4 3560 3240
6.5 24 25 0.408 5650 5150
10 22 23 0.64 8680 7868


DISTRIBUTION & PROTECTION
The simplest method of connecting the extension instruments to the P.A.B.X. unit is to use separate line wires for each telephone.  A saving in line wire and space, with a gain in neatness, may often be achieved by running a multi-core cable from the P.A.B.X. unit to a distribution box so situated that only short lengths of wire are required to connect each telephone instrument to the distribution box.
The exchange equipment must be protected against high voltages and heavy currents that may accidentally be introduced into external lines.  The lines to the public exchange and all external open-wire extension lines must be connected to protection apparatus before being extended to the P.A.B.X. unit.  The use of a distribution frame which mounts all the protection apparatus, is recommended for this exchange.  All the exchange lines and extension lines terminate on one side of the frame, and cables from the automatic unit terminate on the other side.  The two sides can be cross-connected as desired.  Changes in the allocation of extension numbers, and line testing, are simplified by the use of a distribution frame.
When a distribution frame is not employed, the G.E.C. protector, Cat. No. PR1111, containing fuses and electrodes is recommended for connexion to the exchange lines and external extension lines.  Protectors for the exchange lines are often supplied by the public exchange administration.

ORDERING INFORMATION

Line Circuits Link Circuits Dimensions Weight Catalogue
Exchange Extension ins cms lb Kgs
4 24 4 82 x 23 x 20 209 x 60 x 50.5 460 209 PB2624
8 49 8 82 x 47 x 20 209 x 120 x 50.5 920 418 PB2649


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 48/52-volts D.C.

For 4 + 24 line unit
Catalogue Number - SU3203
Dimensions: 20 x 15.5 x 9-ins (53 x 39 x 24cms)
Weight: 621b (28.3kgs)

For 8 + 49 line unit
Catalogue Number - SU3204
Dimensions: 48 x 19 x 144ins (122 x 48 x 37cms)
Weight: 2381b (108kgs)

Automatic Float Battery Charger for operation from a 100/120 or 200/250 volt 50/60c/s single-phase mains supply, having an output of 48/52 volts, 0-3amp DC, and suitable for
charging a 24-cell lead-acid battery.

For 4 + 24 line unit and 8 + 49 line unit
Catalogue Number - SU4202
Dimensions : 20 x 15 x 9ins (53 x 39 x 24cms)
Weight : 761b (34.6kgs)

24-Cell Lead-Acid Storage Battery less stand, acid, and accessories, capacity 20 ampere-hours (or 30 ampere-hours) at the ten hour rate of discharge.

For 8 + 49 line unit
Catalogue Number - BA1103

For 8 + 49-line unit
Catalogue Number - BA1104


Taken from the GEC Catalogue Leaflet No. PXL 09 (Date unknown but later than 1959)


4 + 24/8 + 49 LINE PRIVATE AUTOMATIC BRANCH EXCHANGE

The G.E.C. 4 + 24/8 + 49-line private automatic branch exchange has an ultimate capacity of eight lines to the public exchange and forty-nine extensions.  The exchange is supplied in two units; the first unit is a complete exchange in itself having a capacity of four lines to the public exchange and twenty-four extensions, and the second unit is added when required, to bring the exchange up to its ultimate capacity.  One extension calls another by dialling two digits.   An extension obtains direct access to the public exchange by dialling "9".   This direct access is given to selected extensions and withheld, if desired, from others.   All extensions can gain access to the public exchange via the P.A.B.X. attendant by dialling "0".

An incoming call from the public exchange is signalled on an attendant's cabinet, and extended to the wanted party by the attendant.   Up to eight extension-to-extension conversations can be held simultaneously when two units are installed, and up to four for the single unit.   When an extension makes a call to the public exchange, the connecting link in the P.A.B.X. is in use only while the connexion to the exchange line is being established.   The link is then released for use by the next caller.
 

The P.A.B.X. will work to public automatic and C.B. manual exchanges.   If the public exchange is of the magneto or C.B.S. type, an auxiliary unit is supplied to effect the necessary signalling.

Font View Rear View

Each automatic exchange is housed in a dust-proof sheet-steel cabinet, 6' 10" x 1' 1l" x 1' 8" (209 cms x 60 cms x 50.5 cms).  The cordless attendant's cabinet is attractively designed to stand on a desk or table, it's size being 9.5" x 1' 2" x 9" (24 x 34 x 23 cms).

The complete P.A.B.X. system consists of the automatic unit, attendant's cabinet, telephones, magneto extension bells, when required, for night-service working, line wires from the unit to the telephones, power supply equipment, and protection apparatus for all lines that run outside buildings.   A distribution frame on which all lines are terminated, and all protection apparatus mounted, is recommended for use with the 8 + 49 line exchange, but is not necessary for the 4 + 24-line exchange.

FULL INTERCOMMUNICATION
Any extension user is connected to any other extension by dialling the appropriate number.  The extensions are normally numbered from 21 to 69, or from 21 to 44 with the 4 + 24 line P.A.B.X.

OUTGOING CALLS
Direct access to the public exchange is obtained by dialling the single digit "9".  If the public exchange is automatic, the caller then dials the number of the required subscriber : if the exchange is manual, the call is completed by the public exchange operator.  Certain extensions may be barred from this facility, if desired, by a simple adjustment to the strapping in the automatic unit.
Alternatively, calls to the public exchange can be made via the attendant's cabinet, access to which is obtained by dialling the single digit "0".  On dialling "0", an extension is connected to one of the two "0" level calling lamps on the attendant's cabinet.  the lamp flashing to indicate the call.  The attendant answers the call by operating a lever-type key associated with the calling lamp.  The extension may now replace his handset, and is recalled by the attendant when the call matures.  All extensions may obtain calls to the public exchange via the attendant.  and equipment is provided for two simultaneous "0" level calls.  If both the "0" level lines to the attendant's cabinet are in use, a third party dialling "0" may hold on.  He would then be connected to the attendant automatically when one of the lines became free.

INCOMING CALLS
An incoming call from the public exchange causes an associated lamp on the attendant's cabinet to flash.  The attendant answers the call by operating the key corresponding to the flashing lamp, and extends the caller to the required extension by key-calling the extension number on a strip of digit keys of the plunger type.  If the called extension is free, the exchange lamp on the cabinet glows continuously until the call is answered, when the lamp is extinguished.  If the called extension is engaged on an internal call, the exchange line lamp flashes (at a different frequency to the calling signal) and the attendant can operate the trunk-offering key and offer the incoming exchange call.

CALL-BACK AND AUTOMATIC TRANSFER
An extension engaged on a call over an exchange line may hold the call (by pressing a button on his telephone), while he calls another extension.  At the end of the conversation with the second extension, he resumes his conversation on the exchange line by depressing the button again.  Alternatively, if he wishes, he may transfer the exchange line to the other extension merely by replacing his own handset.
Any telephone may receive a transferred call if it is fitted with a push-button the user may transfer the call again.  By pressing the push-button twice in succession, an extension can recall the attendant by causing the associated exchange-line lamp to flash.

MANUAL EXTENSIONS
Four lines are connected direct to the attendant's cabinet.  These are additional to the 49 automatic extensions and are for those extensions who desire the attendant to establish their calls, whether internal or external.  The telephones of these extensions are not fitted with a dial, and when the caller lifts his handset, a lamp flashes on the cabinet.  The attendant answers, establishes the connexion, and then rings- back to the caller.

NIGHT SERVICE
Night-service working is established by the operation of the night-service key on the attendant's cabinet.  Two methods of operation may be used, the required one being selected by the simple adjustment of the strapping on a terminal block.
In the first scheme, one particular extension is selected to answer all the incoming calls at night.  An incoming call rings this extension's telephone bell, and to answer the call, the extension lifts the handset and dials "8".
In the alternative scheme, an incoming call at night rings separate bells at different selected places.  The call is answered at any extension by lifting the handset and dialling "8".  For this arrangement the number of bells required should be specified when ordering.
In either system, the call is transferred to a further extension, if necessary, by means of the call-back and automatic transfer facility.

AUTOMATIC UNIT
The automatic switching apparatus is mounted in one or two steel cubicles, which have lift-off doors front and rear, to give easy access to the equipment.  Easily-removable metal covers protect the relays against dust and damage.  All the apparatus is the same as that standardised for large public exchanges in many parts of the world and includes the G.E.C. SE50 two-motion selector.  Throughout, the unit and apparatus is designed to give ease of maintenance.

ATTENDANT'S CABINET
The compact cabinet, on which the manual equipment is mounted, is constructed of steel, and the hinged key shelf and rear wall open up to give easy access to the wiring and components.
Calls to the attendant's cabinet are signalled on any of the fourteen calling lamps of which eight are associated with lines from the public exchange, four with the P.A.B.X. manual extensions, and two with calls from the automatic extensions.  The call is answered by the simple operation of the key associated with the flashing lamp.
A strip of plunger-type digit keys provide key-calling facilities to allow calls to be rapidly connected to the wanted extensions.  The attendant's cabinet is also equipped with a dial for use on calls to the public exchange, the dial being switched out of circuit when not in use.
Other keys on the switchboard provide for supervisory facilities, night service, and the extension of alarms from the automatic unit.

POWER SUPPLY
The exchange operates on a 50-volt DC power supply.  When the mains supply is AC, the DC supply may be obtained from a mains unit or from storage batteries.  A G.E.C. mains unit is recommended except where the mains supply is unreliable, when a storage battery is necessary to maintain continuity of service.  When a battery is 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.

Further information regarding the is given in G.E.C. Leaflet SUL 1.

Where the mains supply is DC, the rheostat should be used to step the mains voltage down to the voltage required to charge the batteries.  With this arrangement a charge-discharge system must be used so that the battery connected to the mains is isolated from the exchange.

RINGING AND TONES
Dial and ringing tones, together with ringing current are generated by means of vibrating generators and NU (number unobtainable) and busy tones by a valve oscillator, fitted in the automatic unit.

ALARMS
Two alarm lamps are fitted on the attendant's cabinet, one for deferred alarms and the other for urgent alarms.  The deferred-alarm lamp lights to indicate a P.G. (permanent glow) condition within 30 to 60 seconds of the condition being set up.  The urgent-alarm lamp lights to indicate one of the following: release alarm, ringing-fail alarm, or fuse alarm.  An audible alarm with cut-off key is associated with the alarm lamps.

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 "G.E.C. 1000" Telephone, and the Muraphone "K", described in G.E.C. Leaflet STL.13.
A telephone fitted with a push button is supplied for any extension requiring the call-back and automatic transfer facility.  When ordering, please state the number of telephones required with push-buttons fitted.

SECRETARY'S SERVICE
A secretary may be provided with a G.E.C. switching telephone so that all calls to an executive may be filtered.  The executive would have a G.E.C. Extension telephone.  Calls between executive and secretary are not routed through the P.A.B.X. Full details of this service are given in the G.E.C. Leaflet MTL.2.

LINE WIRES
Any insulated twin conductor, suitably protected if exposed to risk of damp or mechanical damage may be used to connect the telephones to the exchange provided the line loop resistance does not exceed 900 ohms.  A third wire must be connected from the telephones of extensions having the call-back and automatic-transfer facility to a nearby earth point.  If there is no convenient earth point, the third wire must be run to the exchange unit.  The following table gives examples of maximum lengths for various line wire conductors.

Size of Copper Conductors Maximum Permissible Length of Cable Pair
lb/mile AWG (B & S) SWG mm Diam. Yards Metres
4 26 27 0.4 3560 3240
6.5 24 25 0.408 5650 5150
10 22 23 0.64 8680 7860


DISTRIBUTION & PROTECTION
The simplest method of connecting the extension instruments to the P.A.B.X. unit is to use separate line wires for each telephone.  A saving in line wire and space, with a gain in neatness, may often be achieved by running a multi-core cable from the P.A.B.X. unit to a distribution box so situated that only short lengths of wire are required to connect each telephone instrument to the distribution box.
The exchange equipment must be protected against high voltages and heavy currents that may accidentally be introduced into external lines.  Both the lines to the public exchange and all external open-wire extension lines must be connected to protection apparatus before being extended to the P.A.B.X. unit.  The use of a distribution frame which mounts all the protection apparatus, is recommended for this exchange.  All the exchange lines and extension lines terminate on one side of the frame, and cables from the automatic unit terminate on the other side.  The two sides can be cross-connected as desired.  Changes in the allocation of extension numbers, and line testing, are simplified by the use of a distribution frame.
When a distribution frame is not employed, the G.E.C. protector, Cat. No. PR1111, containing fuses and electrodes is recommended for connexion to the exchange lines and external extension lines.  Protectors for the exchange lines are often supplied by the public exchange administration.

G.E.C. 4 + 24 / 8 + 49 LINE P.A.B.X.

Line Circuits Link Circuits Dimensions Weight Catalogue Number
Exchange Extension in cms lb Kgs Standard Tropical
4 24 4 82 x 23 x 20 209 x 60 x 50.5 460 209 PB2501 PB2601
8 49 8 82 x 47 x 20 209 x 120 x 50.5 920 418 PB2502 PB2602

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 48/52-volts D.C.

For 4 + 24 line unit
Catalogue Numbers - Standard SU1109 & Tropical SU1209
Dimensions: 20 x 15.5 x 9-ins (53 x 39 x 24cms)
Weight: 62lb (28.3kgs)

For 8 + 49 line unit
Catalogue Numbers - Standard SU1106 & Tropical SU1206
Dimensions: 48 x 19 x 144ins (122 x 48 x 37cms)
Weight: 238lb (108kgs)

Power Supply Unit for operation from any alternative single-phase mains supply, having an output of 48/52-volts DC.
Dimensions: as above.

4 + 24-line unit
Catalogue Numbers - Standard SU2109 & Tropical SU2209

8 + 49-line unit
Catalogue Numbers - Standard SU2106 & Tropical SU2206

Automatic Float Battery Charger for operation from a 200/250 volt 50/60c/s single-phase mains supply, having an output of 48/52 volts, 0-3amp DC, and suitable for
charging a 24 cell lead-acid battery.

For 4 + 24 line unit
Catalogue Numbers - Standard SU1110 & Tropical SU1210
Dimensions: 20 x 15 x 9ins (53 x 39 x 24cms)
Weight : 76lb (34.6kgs)

For 8 + 49 line unit
Catalogue Numbers - Standard SU1104 & Tropical SU1204
Dimensions: 20 x 15 x 9ins (53 x 39 x 24cms)
Weight : 76lb (34.6kgs)

Automatic Float Battery Charger for operation from any alternative mains supply, having an output of 48/52-volts 0-2 amp DC (or 0-3 amp DC), and suitable for charging a 24 cell lead-acid battery.
Dimensions:  as above.

4 + 24-line unit
Catalogue Numbers - Standard SU2110 & Tropical SU2210

8 + 49-line unit
Catalogue Numbers - Standard SU2104 & Tropical SU2204

24-Cell Lead-Acid Storage Battery less stand, acid, and accessories, capacity 20 ampere-hours (or 30 ampere-hours) at the ten hour rate of discharge.

For 4 + 24 line unit
Catalogue Numbers - Standard BA1103 & Tropical BA1103

For 8 + 49-line unit
Catalogue Numbers - Standard BA1104 & Tropical BA1104


Taken from the GEC Catalogue Leaflet No. PXL 01C (Date unknown)

An advert for this model can be found in GEC Telecommunications - Number 15 (November 1952)

 

 
 
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Last revised: October 07, 2010

FM2