HOUSE TELEPHONE SYSTEMS
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.
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.
House Telephone - Paired
Each telephone had a press button, on the wall rosette, which was used to call the other telephones bell.
Diagram No. TL 230.
The speaking circuit consists of a common pair throughout the system to which all five micro-telephones are connected in parallel. A 4-cell Leclanché Battery No. 1 with circular zincs, is connected across this circuit at the main station and an inductor coil 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
Diagram No. TL 231.
House Telephones - Non-secret - Full intercommunication (Central Battery)
Selective ringing is obtained by the provision of five additional wires
throughout the system, numbered 1 to 5 on the diagram.
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.
House Telephones - Secret - Full intercommunication (Local Battery)
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 Leclanché 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. Figure 2 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.
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)
Admiralty Switch Circuit
The HTS No. 1 was introduced in 1959 and made obsolescent in October 1973.
The HTS No. 2 was introduced in 1967.
The ITS No.3 CCU was manufactured by BT Fulcrum.
All systems were rented.
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 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.
Last revised: November 22, 2021