1. the person using the master station may carry on conversations without the use of a handset and from any part of the room;
2. it is possible to arrange telephone conferences;
3. if in a conference in the manager's room certain information is wanted the person capable of giving this information is called up and can take part in the conversation even better than if he were present since he will have access to the necessary files and data;
4. the manager will never receive busy signal when calling up other persons;
5. the speech is reproduced clearly both in the loudspeaker and in the receivers of the telephone instruments;
6. the speech volume is unimpaired even during conferences involving several telephone instruments;
7. all conversations are secret, i.e., they can only be heard at the stations connected by the manager;
8. the telephone instruments and other apparatus are simple and easy to operate;
9. the system is unequalled for reliability of operation;
10. low maintenance cost is ensured through the absence of amplifiers and other complicated devices;
11. all apparatus is attractive and pleasing in design.

An installation on this system is composed of one master station consisting of an executive's switchboard HF 110 or HF 120, a loudspeaker RD 1100, and a microphone RC 2100 or RC 2110, and telephone instruments BC 2055 or DF 250 for the other stations. The construction and operation of the apparatus is described under the various instruments.

HF 110 &  HF 120
Executive's switchboard
The switchboard consists of a case of reddish brown polished birch mounted on a nickel plated frame of welded steel tubes. A key with a corresponding indicator for each side station is fitted at the front of the apparatus. All parts such as transformers, DC bells, relay etc. are fitted inside the case. The case is fixed to the frame by means of four screws.

There are two types of the switchboard:
HF 110 for 10 lines,
HF 120 for 20 lines.

The switchboard is connected to the wall fitting by means of a flexible cable and in addition it is provided with an extra receiver which is connected when lifted, the loudspeaker being disconnected at the same time. There is also a press button for disconnecting the bell, should the manager not wish to be disturbed.

Dimensions:
height 750 mm, width 535 mm, depth 450 mm, weight HF 110 17 kg, HF 120 19 kg.

A side station is called from the master station by throwing the corresponding key in bottom position which will ring the bell of the side station. As soon as the key is released it returns to middle or speaking position. The speech from the side station is reproduced in the loudspeaker. The conversation is secret, i.e. it cannot be overheard unless additional keys are thrown. When the master station is called from a side station the corresponding indicator is actuated; when the corresponding key is thrown the indicator returns to home position and communication with the side station is established.

RD 1100
Loudspeaker

The loudspeaker is of the moving-coi1 type and has a permanent magnet. It reproduces the speech in a pure and undistorted manner. It is fitted in a case of the same colour and material as the executive's switchboard.

Dimensions:
height 380 mm, width 406 mm, depth 231 mm, weight 8.7 kg.

RC 2100 & RD 2110
Microphones

The microphones designed for this system can pick up and reproduce even comparatively feeble speech, no matter from what part of the manager's room it comes. There are two types of micro-phones: RC 2100 in a case of wood and RC 2110 in a case of soapstone.

RC 2100 is fitted in a cover of wood of the same colour as the switchboard and the loudspeaker. It has a red warning lamp placed below the micro phone proper.

Dimensions:
height 126 mm, width 133 mm, depth 77 mm, weight 1 kg.

RC 2110 is fitted in a cover of soap stone with a frame of dull nickel plated brass. A red warning lamp is placed in the top right hand corner.

Dimensions:
height 131 mm, width 142 mm, depth 77 mm, weight 2.2 kg.

The red warning lamp lights up as soon as a key has been thrown on the switchboard. If after the conversation has been finished a key should not have been returned to home position the lamp remains lit, indicating that conversation in the manager's room may be overheard elsewhere.

Taken from the L. M. Ericsson Telephones and Signalling Material Catalogue No. 188 (1934)

Last revised: March 27, 2024