House Telephone Systems are just intercom systems and there is no connection to the local exchange.  Introduced early 1900's these were also known as Parlour phones and these small intercom systems were installed in residential homes and small businesses.  From a pair of telephones to 5, 10 and 15 terminal systems, these were cheap to run and easy to use.

The only issue was the maximum size of system which was based on the size and cost of the telephones and wiring.  Over 20 extensions it was probably cheaper to install a switchboard.

Systems were powered originally by batteries, but small power units took over in the 1960's.  Due to the miniaturisation and lower cost of automatic telephone systems (PABX), HTS/intercom systems are virtually non-existent today.

Many houses had bell call systems and the wiring could be used for a simple house system.  The NTC sold a house telephone specifically for this purpose.

BT's intension was to withdraw all HTS/ITS systems by September 1992 and all identified customers were contacted by sales groups to encourage a change out for a modern system.

Click here for a generator signalling, private circuit arrangement for two connected telephones.

House Telephone - Paired
This system used two Telephone No. 29's and was introduced circa 1917.  The two telephones were just connected together using 3 wires.  Powered by a centrally positioned battery of 3 cells and includes a "Coils, Inductor, 3 terminal", which comprised of two 17ohm coils.  This system could not be expanded.

Each telephone had a press button, on the wall rosette, which was used to call the other telephones bell.

Diagram No. TL 230.

House Telephones - Non-secret - Without full intercommunication
A system can consist of up to 10 extensions and is also known as a Delta system, which refers to the simple stations with only connectivity to the main.  The diagram shows a system of five stations fully wired.  The main station has full intercommunication, but all other stations are limited to communication with or through the main station as they cannot call each other.

The apparatus at all stations consists of:-
1 x Hand Microtelephone,
1 x Trembler Bell,
1 x Press Button.
In addition, the main station has a selector switch.

The speaking circuit consists of a common pair throughout the system to which all five micro-telephones are connected in parallel.  A 4-cell Leclanche Battery No. 1 with circular zincs, is connected across this circuit at the main station and a "Coils, Inductor, 3 terminal" being placed in one of the battery leads to prevent accidental short circuiting.  To enable each station to call the main, a third wire is run from one side of the main station bell, and tees taken off to the press buttons of the other stations.  When a press button is operated the ringing circuit is completed through one wire of the speaking circuit, one winding of the inductor coil, and thence, through the battery, to the other side of the main station bell.

Direct ringing to the sub-stations required (otherwise known as selective ringing) is provided at the main instrument through the selector switch. For this, four other wires are necessary, one to each bell, and the circuit is completed through the bell to one wire of the speaking circuit, thence through the battery, through one side of inductor coil and main station press button, to selector arm.

It will be seen that the main station can speak to all stations at once, or can, by calling up the required station, put stations in communication with each other.

Diagram No. TL 231.

Main Station - Telephone No. 33 (5 way wall) or Telephone No. 35 (10 way wall)
Extensions - Telephone No. 31 (1 way wall)


House Telephones - Non-secret - Full intercommunication (Central Battery)
This system was also called Direct Call.  The diagram shows a system of five stations fully wired, but the systems maximum can be 15 extensions, depending on the telephones used.  The apparatus at each station is identical, and consists of hand micro-telephone, trembler bell, press button and selector switch. A battery of four cells (Leclanché No. 1 C.Z.) is placed at a central point in the system, with a "Coils, Inductor, 3 terminal" in line one battery lead to prevent accidental short circuits.  The speaking circuit consists of a common pair of wires throughout the system.  The battery is connected across this pair and the five hand micro-telephones are connected to it in parallel. Therefore one conversation only is possible at any time, and any number of stations may take part.

Selective ringing is obtained by the provision of five additional wires throughout the system, numbered 1 to 5 on the diagram.  No. 1 wire is connected to the bell at No. 1 station, and is teed-in to the No. 1 contact stud on the selector switches of the other stations. The bell circuit is completed through the selector switch and press button of any station, through one wire of the speaking circuit to one side of the inductor coil, and thence through the battery and back to the other side of the bell at No. 1 station.  The other wires (Nos. 2, 3, 4 and 5) are connected to the bells of their respective stations, and to corresponding contact studs at all other stations in exactly similar fashion. The usual method of operating is as follows:-

First listen-in to ascertain if the circuit is disengaged. If clear, turn the selector switch to the number of the station required, press the ringing button and await reply. It is not necessary to have the selector switch in any particular position to take an incoming call.

Diagram No. TL 232.

Extensions - Telephone No. 33 (5 way wall) or Telephone No. 35 (10 way wall) or Telephone No. 51 (15 way wall) or  Telephone No. 50 (5 way table) or Telephone No. 52 (10 way table).


House Telephones - Secret - Full intercommunication (Local Battery)
This system was called Direct Call - Secret.  Referring to the diagram, Figure 1 shows four stations fully wired, but the system maximum is 20 dependant on the telephones used.

The apparatus at all stations is identical and consists of:-
1 x Hand micro-telephone,
1 x Switch hook,
1 x Selector switch,
1 x Press button,
1 x Ringing vibrator,
1 x Cut-in-relay,
1 x Induction coil,
1 x Local battery,
1 x Trembler bell.

The main cable to all stations consists of one wire per station, plus two wires to distribute power for ringing from a battery of three Leclanche cells, No. 1, C.Z., fitted in a central position on the system.

In describing this system it is best to follow out the procedure for establishing a connection. The Figure below shows No. 1 calling up No. 2. No. 1 has moved his selector switch to No. 2 stud and pressed his calling button. Following the connections from No. 1 selector to No. 2 switchhook, which is depressed and making contact on the bottom spring if No. 2 is not already using his telephone, the circuit is joined up through No. 2 bell to the positive side of the battery and thence through battery and out on negative line to No. 1 ringing vibrator coil and press button. An intermittent current flows through this circuit as the trembler bell at No. 2 alternatively breaks and makes connection and this current actuates the armature of the No. 1 vibrator coil in unison with the movements of the trembler bell hammer, giving out an audible clapping sound which signifies to No. 1 that the No. 2 station is not engaged and is being rung.

No. 2 now lifts his receiver, breaking the bell circuit at the switchhook and connecting No. 2 line direct to his selector switch through the winding of his cut-in relay, battery and press button contacts, see Figure 3.  Whilst listening on the line No. 2 turns his selector switch over the contact studs, stopping on the stud on which he hears a click in his receiver. This click is produced by the operation of the cut-in relay when a full circuit is established. The complete connection in this case will he through No. 2 selector to No. 1 stud and via No. 1 line to No. 1 switchhook, cut-in relay, battery, press button and selector.

The local speaking circuit of each instrument is completed through a contact on the cut-in relay which connects up the side circuit containing primary of induction coil and transmitter, the receiver being in a closed circuit through the secondary winding of the induction coil.

It will be seen that a conversation in progress between two stations cannot be interrupted by a third station as communication with another station can only be obtained by that station co-operating in building up the circuit by placing its selector switch in connection with the Home Line of the station desiring to speak with it.  The term "home line" is given to the line which is joined up to the switchhook of a particular station and to corresponding studs on the selector switches of other stations.

Figure 4 shows an unsuccessful attempt on the part of station No. 3 to ring up No. 2 when the latter is engaged.  No. 2 bell is disconnected at the switchhook and the ringing circuit is therefore incomplete.

Diagram No. TL 233.

Extensions - Telephone No. 39 (5 way wall) or Telephone No. 41 (10 way wall) or Telephone No. 43 (15 way wall) or Telephone No. 45 (20 way wall) or Telephone No. 56 (5 way table) or Telephone No. 58 (10 way table) or Telephone No. 60 (15 way table) or Telephone No. 62 (20 way table)

A Telephone No. 37 (1 way wall) or Telephone No. 54 (1 way table) may also be used on this system but it has very restricted functionality.


Admiralty Switch Circuit
This was a Parsons Sloper secret system.  No additional information available.

HTS No.1
A press button telephone intercom system with table or wall mounted telephones (similar in appearance to 300 type instruments) with 5, 10 or 15 buttons depending on system size, maximum system size is 15 stations. The telephones are interconnected by multi-pair cabling (12 wire for 5 station systems, 21 wire for 10 or 15 station systems) and locally powered by dry batteries.

The HTS No. 1 was introduced in 1959 and made obsolescent in October 1973.

Q 351,352 & 353.

TI's C3M 4000 & E5D 7301.

HTS No.2
A press button telephone intercom system with table or wall mounted telephones (similar in appearance to 706 type instruments) with 5, 10 or 15 buttons depending on system size, maximum system size is 16 stations. The telephones are interconnected by multi-pair cabling (21 wire for 6 stations, 24 wire for 11 stations and 41 wire for 16 stations) and powered by a mains Power Unit No. 53.

The HTS No. 2 was introduced in 1967.

Q 361 & 362

TI's C3M 4001 & E5D 7302.

ITS No.3 (PROTEUS 24 and 64)
Fitted with standard type 'Dial' or 'Press Button' LD signalling telephones connected to a free standing self-contained Central Control Unit (CCU) containing electronic switching and control circuitry. Was marketed under the name of Proteus. The telephones are 2-wire connected to the CCU via twisted pair cabling. Maximum capacities 24 or 64 stations depending on type of backplane and line interface equippage.  The system is mains powered by a Power Unit No. 155A contained within the CCU.

The ITS No. 3 was introduced in 1982.

The ITS No.3 CCU was manufactured by BT Fulcrum.

All systems were rented.

Customer Apparatus Guide Notes 'Proteus 24 & 64' (Site documentation supplied with system).
TI's C3M 4010 & E5D 7302.

HTS and ITS Parts

Description                                                       BT Item Code

HTS No 1:-
Telephone  House   100,  (5 stations - table model)                   42  1902
Telephone  House   101,  (5 stations - wall model)                    42  2034
Telephone  House   102,  (10 stations - table model)                  42  1903
Telephone  House   103,  (10 stations - wall model)                   42  2035
Telephone  House   104,  (15 stations - table model)                  42  1904
Telephone  House   105,  (15 stations - wall model)                   42  2036

HTS No 2:-
Telephone  House   500,  (5 stations - table model)                   42  0153
Telephone  House   501,  (5 stations - wall model)                    41  0192
Telephone  House   502,  (10 stations - table model)                  41  0154
Telephone  House   503,  (10 stations - wall model)                   41  0155
Telephone  House   504,  (15 stations - table model)                  41  0156
Telephone  House   505,  (15 stations - wall model)                   41  0193
Power Unit No. 53B                                                    31  4065

ITS No 3:-
Proteus Power Unit No. 155A                                           43  200#
Proteus Case   246 A                                                  43  201#
Proteus Case   246 B                                                  43  202#
Proteus Card   1A1/FDH 16891 (Red Handle)                             43  203#
Proteus Card   1A1/FDH 16900 (Yellow Handle)                          43  204#
Proteus Card   1A1/FDH 10894 (Blue Handle)                            43  206#
Proteus Card   Common Control PCB                                     43  209#
Fuses 3 Amp,   500 mA, 1 Amp (spares supplied with CCU)
BT Repair Services (Formerly Fulcrum) Item Code numbers.
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Last revised: November 12, 2023