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TEL/11D, TEL/12D, TEL/13D and TEL/14D


The principal aim of telephone designers has always been to raise the convenience of telephone conversation to the same level of facility as exists in normal direct conversation between two-people. The G.E.C. Loudspeaking Master Station brings its user very near to that objective. When conversing with any sub-station on the system the user has complete freedom to move about the room, or to make notes and consult references. Both hands are free and there is as little restriction as if the other party were in the same room.

The master station includes a single stage transistor amplifier to raise the level of the received speech to that required to operate the loudspeaker. This has the advantages over the previous master station system that the signals between the substations and the master station do not have to be carried by screened cables, and that the master station circuitry can be simplified.

The amplifier operates from a 6-volt battery, no mains supply being required.

A simple switch is included to give increased volume, when required.

This loudspeaking instrument is supplied as part of an inexpensive but highly-efficient intercommunication telephone system, which is particularly suited to the requirements of the business organisation of limited size. In large organisations, the system is invaluable as an auxiliary to the main telephone system, to provide directors and executives with immediate communication with their close associates.

By means of his Master Station, the executive can dominate the system, exercising complete priority in communication.  He can call any substation whether or not it is engaged and he can also obtain substation conference facilities when required.

Two sizes of instruments are available - one to provide for systems up to 11 stations and the other up to 21 stations - either of which can include one, two or three master stations. All parties can engage in separate simultaneous conversations.

The Loudspeaking master Station is housed in a polished cabinet of pleasing modern design. The double-throw keys provide connections to up to twenty substations.  The keys identified by names on plastic labels, which can easily be changed desired.  The loudspeaker is fixed behind a grill in the bottom off the cabinet, and the cabinet raised to a height above desk level such that the output is at an optimum level. The handset is provided to allow a more intimate conversation, when required.

To initiate a call from a master station to a substation the relevant key is operated. The key has two operated positions, a locking speak position and a non-locking ring position, which is located by depressing the key past the speak position. Thus, the substation buzzer only sounds while the key is held operated. The calling lamp at the substation remains lit until the call is answered. The master station should restore the key to normal at the end of the conversation.

Two or more substations can be called simultaneously for conference purposes and additional stations can be brought into a conversation at any time.

When the call is received by the substation, a panel on the substation-set is illuminated and a buzzer note is heard. The called substation is therefore given both audible and visual warning that a priority call from a Master Station is coming through. Should the substation be already engaged, no buzzer note is heard, but the panel is illuminated, indicating that a priority call is waiting. By pressing a button, the substation releases the existing call and is immediately connected to the Master Station.

When one master station calls another then either the calling party uses the handset or, by prior standing arrangement, the called party, noting from the illuminated name panel that the call is from a Master Station, takes the call on his handset. Thus the senior Master Station may use the loudspeaker for all his calls.

When a call is received by a master station warning is given by a buzzer note. At the same time the panel bearing the name of the calling station is illuminated. To complete the connexion, the switch associated with the calling station is depressed. Should the Master Station be already engaged a buzzer note is not heard, but the name panel will still glow. For quiet surroundings, the touch of a switch cuts off the buzzer and calls are then signalled by a click from the buzzer for each depression of the push key by the caller.

When the Master Station user is talking to a substation and desires a more intimate conversation, he can transfer to the handset by the simple action of lifting it from its position at the side of the cabinet. The loudspeaker is then cut off automatically.

TEL/5D/SUS/17 Table mounted TEL/5D/SUS/19 Wall mounted

The Substation Sets, with 10 or 20 push buttons and lamp panels for three Master Stations are pictured above.  These are plastic cased and can be table or wall mounted.

Gecophone Junior sets are used for Direct Working between secretary and executive, where the secretary only needs to communicate with the executive.  The Reply and Call Gecophone Junior is used in these instances.  See picture below.


  • The general intercommunication system requires a d.c. supply of 4.5 volts for ringing and 1.5 volts for speaking. The former is derived from a battery of three dry cells and the latter from a single dry cell, both being situated approximately at the mid-point of the system.
  • Two additional 6-volt d.c. supplies are required for the operation of each master station and should be derived from two batteries of four dry cells.
  • Suitable dry cells for the supply batteries are the G.E.C. Long Life 1.5 volt Round Cell type (7” x 2.5”dia.), Catalogue No. BA4955. (Standard and Tropical).

Loudspeaking Master Station - 17lbs (7.7Kgs)
Substation Sets - 11.5lbs (5.2Kgs)


  Standard Finish Tropical Finish
10 Line 20 Line 10 Line 20 Line
Loudspeaking Master Station TEL/11D/LTS TEL/13D/LTS TEL/12D/LTT TEL/14D/LTT1
Substation for 1 Loudspeaking Master Station TEL/5D/SUS/14 TEL/5D/SUS/17 TEL/6D/SUT/6 TEL/6D/SUT/9
Substation for 2  Loudspeaking Master Stations TEL/5D/SUS/15 TEL/5D/SUS/18 TEL/6D/SUT/7 TEL/6D/SUT/10
Substation for 3 Loudspeaking Master Stations TEL/5D/SUS/16 TEL/5D/SUS/19 TEL/6D/SUT/8 TEL/6D/SUT/11

Substations can be table or wall mounted

Take from the GEC Catalogue Leaflet No. ITL 3

Introduced circa 1961.

GEC Telecommunications journal article

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Last revised: November 29, 2021