In 1955 GEC decided to renumber all their telephones with the prefix
TEL. The MT 41xx, MT 42xx, MT 43xx and MT 44xx series, which was the original part number
range for the
this series of phones were part of this renumbering. Please see the table below for more
information. The GEC Extension Telephone System
The G.E.C. Extension Telephone System
permits two or three telephones to be associated on one exchange line, for exchange calls to be made or received at any of them and for
intercommunication between them. One instrument - the switching telephone
- is fitted with a four position switch; this allows calls to be extended to the
other two, which are called extension telephones. Inter-telephone calls are initiated by operation of
push buttons and signalled by means of buzzers, or, alternatively, can be signalled over pole routes by
magneto calling.
Facilities
- Calls from exchange can be signalled and answered at the switching telephone; if required, they can be instantly switched to either
extension instrument.
- Outgoing calls can be made from any of the telephones, because, at any time, the exchange line can be left switched through. Straps in the switching telephone can be removed to prevent the overhearing of through calls at the switching telephone.
- An intercommunication call between switching and extension telephones is made at the touch of a pushbutton. An exchange call can be held whilst conversation takes place from the switching telephone to an extension. Such a conversation is entirely secret from the exchange caller.
- An extension user can call the switching telephone, even though the extension instrument may be already engaged on an exchange call. Calls can thus readily be transferred from extension telephone to switching telephone.
- In whichever position the switch is left, the bell of the switching telephone is connected across the line to signal incoming
calls.
- The system can be used on either automatic or C.B. manual lines, and requires no modification to the exchange.
For the Telephone Administration
The system replaces the old switching bell set, with its multiplicity of parts, by a compact telephone which is simple to use and pleasingly modern in appearance.
Subscribers will welcome the special facilities offered, with resultant increased revenue to the Administration.
The switching telephone is already widely used by the British Post Office, for whom it was designed by the G.E.C., and is standardised as
Telephone No. 248 with Bell Set No.
39.
For the Business House
In business or commercial premises, the system can be connected to any type of exchange line and proves a valuable aid to speed and efficiency. Incoming calls can be filtered through the switching telephone, under the control of a secretary, and be instantly switched, as required, to the executive or his assistant.
Simplicity of Installation
The system is simple to install, requiring only the following apparatus and connexions:-
- At the switching position - a switching telephone, with an external bell to signal exchange calls and a 3-volt battery for inter-telephone calls.
- Between positions - a 4-wire interconnecting line of any reasonable length. Line, bell and battery connexions are made at moulded plastic terminal blocks, which have robust construction and pleasing appearance.
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Switching Telephone - MT 4150 |
Switching telephone
The switching telephone comprises a handset instrument, with black plastic case and
un-tarnishable metal parts, surmounting a detachable base which accommodates the four-position switch, pushbuttons, buzzer, engaged signal and suppression unit.
Four-position Switch - The switch is robust in construction and foolproof in operation. Its four positions are arranged in logical sequence for easy
operation and are shown in the picture to the right.
Pushbuttons - The pushbuttons (G.E.C. Patent No. 493,649) are self-locating in their holes in the case, and are readily detachable from the springsets.
One or two pushes may protrude through the case, as required, without alteration of wiring. When only one push is in use, the second can be neatly stored within the base in a clip formed by one of the contact springs.
Engaged Signal - A transparent aperture in the base displays an engaged signal whenever a conversation is in progress from exchange to extension.
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Extension Telephone - MT 4301 |
Extension telephone
The extension instrument utilises the same case mouldings as the switching telephone, and is entirely self-contained, with the bell (exchange calls) and buzzer (local calls) mounted within the base.
A pushbutton is provided for calling the switching telephone.
Special Features
The telephones incorporate the following features:-
- Sidetone suppression by means of the well-known Gecophone anti-sidetone circuit.
- Handset cradles are robust and practically unbreakable in normal use. For tropical service an aperture between cradle-lip and case, and a series of holes in the top of the case, permit circulation of air through the interior to minimise
condensation (see picture to the right).
- A closely-coiled wire inside the cradle lip, and protecting gauze over the sound outlet holes prevent ingress of insects.
- A suppression unit is fitted to the buzzers to eliminate interference with nearby radio apparatus.
- Materials and finishes are specially chosen for long service life under tropical conditions.
External Bell
For signalling exchange calls at the switching telephone, suitable bells are those of the G.E.C. Cat. No.
BE 1100 series (standard) and BE 1200 series (tropical).
Automatic or Manual
The telephones illustrated are for use on automatic systems. Alternative instruments are available for C.B. manual systems, the dial being replaced by a moulded dial dummy. In other respects the C.B. telephones are the
same as the automatic instruments and offer the same facilities.
Magneto calling over long Extension lines
Where line wires between switching and extension telephones have to run over a pole route, the convenience of buzzer calling may be sacrificed in favour of magneto calling with the attendant advantage of two line wires
instead of four between main and extension. A generator fitted in a separate box, together with a combined bell and capacitor, can then be installed at the
main station, and a generator and capacitor at the extension position.
Catalogue Numbers
(Numbers in brackets are the later 1955 catalogue numbers)
TELEPHONE |
STANDARD |
TROPICAL |
AUTOMATIC |
MANUAL |
AUTOMATIC |
MANUAL |
SWITCHING TELEPHONE |
MT 4150
(TEL/1S/ATS) |
MT 4151
(TEL/1S/CTS) |
MT 4250
(TEL/2S/ATT) |
MT 4251
(TEL/2S/CTT) |
EXTENSION TELEPHONE |
MT 4301
(TEL/1E/ATU) |
MT 4302
(TEL/1E/CTU) |
MT 4401 |
MT 4402 |
Weight
Switching telephone - 11lbs / 5kgs
Extension Telephone - 7lbs / 3.2kgs
Taken from the GEC Catalogue MTL 2
G.E.C. Exchange Line
Switching Telephone System
The G.E.C. Exchange Line Switching Telephone System permits
selected P.A.X. extensions to be connected to the public exchange, thus
providing P.A.B.X. working for P.A.X. users at low cost. The system provides for
any one of up to 4 exchange lines to be connected to any one of up to 10
selected extensions, which can make or receive public exchange calls The
selected extensions are equipped with switching telephones. These are similar in
appearance and performance to the "G.E.C. 706 " Telephone described in G.E.C.
Catalogue Leaflet No. STL.16, but are mounted on a plinth in which there are six
pushbuttons.
The four exchange lines are connected to four of the
pushbuttons, each of which can be illuminated individually, either continuously
or intermittently, to indicate the state of the exchange lines when the handset
is lifted. The remaining two pushbuttons are for HOLD and RELEASE facilities.
Exchange line calls can be transferred from one switching
telephone to another when required.
Incoming calls from the public exchange are signalled on
bells external to the telephone instruments, the number of bells depending on
the location of the switching telephones, e.g., where several switching
telephones are located near to one another, only one bell would be required to
serve all the telephones.
Both audible and visible warnings are given
to an extension engaged on a call to the public exchange if a second extension
becomes connected to the same exchange line.
Arrangements can be made for a particular extension to answer all the incoming
exchange calls at night.
FEATURES
-
Public exchange line access is given to selected
private automatic exchange extensions at low cost.
-
The system gives up to ten extensions access to up to
four public exchange lines and can be associated with any normal 26-volt or
50-volt P.A.X.
-
The same telephone is used for exchange line calls and
normal P.A.X. extension calls.
-
Public exchange line calls do not use a P.A.X.
connecting link.
-
Public exchange line calls can be transferred to any
other extension having a G.E.C. Exchange Line Switching Telephone.
-
Both visible and audible indications are given of
incoming public exchange line calls.
-
Warning of an incoming call over the P.A.X. is given to
an extension engaged on a public exchange line call by means of a buzzer in
the plinth.
-
Both visible and audible warnings are given of the
intrusion of an extension on to an existing public exchange line call.
-
The associated automatic equipment is accommodated on a
wall-mounted shelf.
-
A calling signal switch can be fitted if required to
distribute the exchange line calling signal to the extensions in a pre-set
sequence.
-
The system can be used with public exchanges of the
C.B. Manual or Automatic type.
The operation of the G.E.C. Exchange Line Switching
Telephone System is by simple depression of push buttons in the plinth. All push
buttons are clearly marked and are used in the following manner:
Incoming Public Exchange Line Calls
An incoming exchange line call can be signalled in one of three ways:-
-
A particular extension may be detailed to answer all
exchange line calls and transfer them to the wanted extension. In this case
the incoming call would be arranged to ring only the external bell
associated with the answering extension.
-
An incoming call may ring bells at all the switching
extensions. The call would then be answered by the first extension to lift
the handset and transferred, if necessary to the wanted extension.
-
A calling signal switch may be fitted which
automatically distributes an incoming calling signal to the extensions in a
fixed sequence.
When an extension lifts the handset to answer an incoming
exchange line call, the lamp in the push button associated with the calling line
flashes in synchronism with the exchange ringing current. To answer the call,
the extension simply depresses the push button. The lamp then glows continuously
and the extension is connected direct to the public exchange line for speech.
Enquiry
If an extension that is participating on an exchange line call wishes to
speak to another PAX extension during the call he presses the HOLD button. This
causes a holding loop to be connected across the exchange line and connects the
telephone to the PAX. The extension can then dial the number of the wanted PAX
extension in the normal way and make an enquiry secret from the exchange line.
At the end of the the enquiry call, the extension resumes his conversation on
the exchange line by again depressing the appropriate exchange line push button.
Any enquiry call can be made to any extension on the PAX.
TRANSFER
An extension participating in an exchange line call can transfer the
exchange line to any of the extensions having a switching telephone, if
required. The same procedure is adopted as for an enquiry call except that when
the called extension answers he is informed that he is wanted on a particular
exchange line. The second extension then depresses the appropriate exchange line
pushbutton and the first extension replaces the handset and presses the release
key.
OUTGOING PUBLIC EXCHANGE LINE CALLS
When a switching telephone user wishes to make a public exchange call, he
lifts the handset and depresses a pushbutton that is not illuminated.
Pushbuttons that are illuminated indicate that the associated exchange lines are
engaged. As soon as the pushbutton is depressed the telephone is connected to
the public exchange and the pushbutton is illuminated.
RELEASE
When the non-locking release pushbutton is depressed, all locking
pushbuttons previously engaged restore to normal. The release pushbutton should
be pressed at the end of all main exchange calls. This reverts the switching
telephone to normal P.A.X. operation, releases the main exchange line and
restores the associated pushbutton to the normal position. Failure to release an
exchange-line pushbutton would leave the exchange line connected to the
particular telephone.
INTERRUPTIONS
Should a switching telephone attempt to gain connexion to an exchange line
that is already in use, or should two telephones answer an incoming call
simultaneously, an interruption tone is heard on the telephone and the
pushbuttons associated with the affected exchange line flash.
NIGHT SERVICE
Arrangement can be readily made for one of the switching telephones to
answer incoming exchange line calls at night when most of the telephones are
unattended.
EXTENSION -TO-EXTENSION CALLS
To make extension-to-extension calls over the P.A.X. it is not necessary to
operate any keys on the plinth. Connexion is obtained in the normal manner by
lifting the handset and dialling the required number.
EXECUTIVE RIGHT-OF-WAY
A further pushbutton can be fitted in the telephone instrument to give the
normal executive right-of-way facility provided as an optional facility on all
G.E.C. private exchanges. This is particularly useful for switching extensions,
who regularly have to transfer exchange calls, to enable them to contact
extensions who may be engaged on internal calls.
EQUIPMENT
Apart from the switching telephones for those extensions who require to make
public exchange calls, the only equipment required additional to the standard
P.A.X. is a relay set for each exchange line.
COLOUR
Exchange Line Switching Telephones are available in black, ivory, and dual
grey.
AUTOMATIC EQUIPMENT
Number of Exchange
lines required |
Description of Equipment necessary
|
Catalogue Number |
26 volt |
50 volt |
1 |
Exchange Line Switching System (Automatic
Equipment) |
ELS261 |
ELS501 |
2 |
Exchange Line Switching System (Automatic
Equipment) |
ELS262 |
ELS502 |
3 |
Exchange Line Switching System (Automatic
Equipment) |
ELS263 |
ELS503 |
4 |
Exchange Line Switching System (Automatic
Equipment) |
ELS264 |
ELS504 |
1 |
Exchange Line Switching System with Calling Signal Switch (Automatic
Equipment) |
ELS271 |
ELS511 |
2 |
Exchange Line Switching System with Calling Signal Switch (Automatic
Equipment) |
ELS272 |
ELS512 |
3 |
Exchange Line Switching System with Calling Signal Switch (Automatic
Equipment) |
ELS273 |
ELS513 |
4 |
Exchange Line Switching System with Calling Signal Switch (Automatic
Equipment) |
ELS274 |
ELS514 |
EXCHANGE LINE SWITCHING TELEPHONES
|
Catalogue Number |
|
26 volt |
50 Volt |
Exchange Line Switching Telephone complete with
plinth |
54460/ATT-1 |
54460/ATT |
Exchange Line Switching Telephone complete with plinth and pushbutton
for Executive Right-of-Way facility |
54470/ATT-1 |
54470/ATT |
Please state quantity and colour of the telephone required with the catalogue
number.
Taken from the GEC Catalogue Leaflet PXL7
GEC 746
105 and 107 Switching Telephone Systems
-
Two or three telephones on one exchange line
-
Comprises a 'main' (switching) telephone and one or two
extensions
-
Maximum line-loop resistance of 1000 ohms
-
Extension can be 9.5 km (6 miles) from the 'main'
telephone
-
Pushbutton switching between telephones
-
Switching-telephone user can deal with all calls
-
Extension-telephone user's calls can be private from
other telephones
-
Also provides an intercom system
The GEC746 105 and 107 switching-telephone systems permit a
'main' (switching) telephone and one or two extension telephones to be connected
to one exchange line. The basic telephones are similar in appearance and
performance to the GEC746 table telephone. However, one telephone in the system
is mounted on a plinth in which there are six pushbuttons to allow calls to be
extended to the extension telephones; these latter instruments have a single
pushbutton.
The system is particularly suitable, for example, for a
doctor who needs to receive emergency calls 24 hours a day and where it is
desirable to have only one telephone number. The 'main' telephone would be at
his surgery and the extension telephone at his home. On leaving his surgery, he
would operate the EXTN TO EXCH button and all calls are automatically routed
direct to an extension telephone in his home. This is typical of many similar
applications (such as the small business with a separate workshop) where the
telephones need to be separated by a considerable distance.
Another application is where one or two executives wish
their secretary (in an adjacent office) to accept all incoming calls and only
pass on those which require their personal attention. If the executive wishes to
make an outgoing call, he can either ask the secretary to dial the number (and
transfer the call to him when the called party answers) or dial the number
himself having asked the secretary to switch the line to his telephone.
The system also provides an intercom system between the
telephones, but under all conditions of usage, an incoming call can always be
given attention.
ABRIDGED SPECIFICATION
'105 and 107' switching telephone systems use the GEC746
table telephone with the necessary switches, lamps and buzzers added to give the
features described in this leaflet; there are four basic versions:
105 internal: 'main' + 2 extension telephones All telephones are in the same
building and
107 internal: 'main' + 1 extension telephone interconnexion is by way of a
6-core cable,
105 external: 'main' + 2 extension telephones interconnexion Extensions
telephones not in the same building as each other and/or the 'main' telephone;
107 external: 'main' + 1 extension telephone is by way of a 2-core cable.
Exterior
Case and handset moulded in ABS high-impact plastic, dual grey (the handset,
cords, dial surround, and switching plinth are the darker tone). Black and ivory
telephones also available. Extension telephones can also be supplied in blue,
red, yellow and dual-green.
Cords
PVC-covered cadmium-tinsel-conductor cords. Held by grommets to relieve
conductors of stresses.
Line cord, straight: 1830 mm (72 in).
Handset cord, coiled: 250 mm (10 in) unextended; 1700 mm (68 in) extended.
Cradle switch
Sealed microswitches.
Dial
Characters printed black on antique-silver background beneath clear plastic
finger plate. Trigger type and self-compensating action. Projects through
self-centring ring on case. No appreciable variations in pulse ratio after 4'/2
million impulses.
Speed: 10 IPS (20 IPS version available). Inter-digit pause: 240 ms minimum.
Break-to-make ratio. 2 to 1 (other ratios can be supplied).
Transducers
Receiver inset: rocking armature, replaceable capsule; sensitivity, + 56 dB
relative to 1 Pa/root W available power.
Transmitter inset: carbon granule, replaceable capsule; sensitivity -10 dB
relative to 1 V/Pa at 2 Pa input.
Regulator
An automatic volume regulator is fitted to limit speech-signal amplitudes on
lines shorter than 400 ohms; introduces virtually no attenuation on longer
lines.
Signalling
Exchange: double-coil ringer, DC resistance 1000 ohms; accepts ringing
currents between 16 and 30 Hz; bells, double gong, harmonizing tones.
Telephone separation: the line-loop resistance should not
exceed 1000 ohms between the exchange and the most remote extension. On
'external' systems the maximum mutual capacitance due to the main-to-extension
lines should not exceed 0.45 uf - equivalent to a total extension-line length of
the order of 9 km (6 miles) when using some of the common 0.5 or 0.6 mm (6.5 or
10 lb) cables.
Intercommunication : DC single-coil buzzer, moving armature
type; DC resistance 55 ohms. On 'external' systems, signalling is via a 20 Hz AC
ringing convertor and the normal telephone bell.
Environment
Suitable for use in tropical climates. Protected against entry of insects.
Dimensions and Weight
|
'main' telephone |
extension telephone |
Height |
152 mm (6 in) |
119 mm (4.75 in) |
Width (over handset) |
250 mm (10 in) |
250 mm (10 in) |
Width (over case) |
140 mm (5.5 in) |
140 mm (5.5 in) |
Depth |
248 mm (9.75 in) |
216 mm (8.5 in) |
Weight (complete telephone) |
2.7 kg (6 lb) |
1.7 kg (3.5 lb) |
Weight (handset) |
230 gm (8 oz) |
230 gm (8 oz) |
Catalogue Numbers
A complete system requires:
One 'main' (switching) telephone type TST4001.
One or two extension telephones, with a single pushbutton type TST1710.
One DC supply: either 12 V DC battery or GEC power unit type D97206T (200-250 V
AC input) or type D97491 T (100-125 V and 200-250 V AC input).
One AC ringing convertor (required for 'external' systems), type D97130T.
Optional facilities
Pushbutton telephones: the telephone can be supplied with a pushbutton
keyset. Two versions are available: one provides loop-disconnect (decadic)
signalling, 10 or 20 IPS, and the other provides DC-leg signalling for suitable
PABX systems.
Loudspeaking telephones: GEC loudspeaking telephones LST4D can be used for the
extension telephones. Direct calling between extensions: on 'internal' systems,
a second pushbutton on extension telephones can be provided for inter-extension
direct calling.
Taken from the GEC Catalogue Leaflet DLT32B 3ME879 (1971)
GEC Telecommunications
journal article
See also TEL/9S
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