TELEPHONE No. 704

BPO Portable linesman's telephone in a green plastic case.  Fitted with a transistorised ringer generator and Handset No. 6.

The telephone has jack for connection of a Headset No. 1.

Uses 3 cells dry R20.

Superseded the Telephone No. 250.

Telephone No. 704 was introduced in 1965, No. 704A in 1968, the No. 704B in 1973 and the No. 704C in 1984.

The 704C had a 20ma line current buzzer to allow two way transmission when connected to modern electronic telephones.

Circuit diagram - N804.

Specification - S986.

It is good practice to remove the three dry cells from the phone, when not in use.  They can corrode very quickly in the battery chamber - you have been warned.

Made by TMC - Model T120.

STC also made a the military version called the PTC405 and this usually didn’t come with a dial as it was used point to point or with a manual switchboard.  It was superseded by the PTC414 aka the Racal RA2000.

TELECOMMUNICATIONS INSTRUCTION
E MAINTENANCE
3 Underground
J0125
Issue 3, Dec 79

OPERATING INSTRUCTIONS
FOR THE TELEPHONE No. 704

1. GENERAL
The Telephone No. 704 is a portable instrument, suitable for connexion to all types of exchange line and designed for use by external staff. A three-position slider switch enables the internal battery to be switched in or out of circuit and, in the non-locking position of this switch, connects ringing current from a transistorised generator to the line terminals. A jack is provided so that a headset can be plugged in and used as an alternative to the handset and two sockets enable the output from an amplifier to be connected to this receiver. A transmitter CUT-OFF button is provided on the handset.

2. PREVENTION OF INTERFERENCE TO WORKING CIRCUITS
When connecting the telephone to a pair in a cable that contains working circuits, prevent possible disturbance to a working circuit as follows:-

1. Set the three-position slider switch to the CB position and connect the telephone to line.
   

2. Press the transmitter CUT-OFF button on the handset before removing the handset from its cradle.
   

3. Check that the line is not in use.

3. AUTOMATIC EXCHANGE LINES

1. Check, as described in par 2, that the line is not in use.
   

2. If the line is not in use, release the transmitter CUT-OFF button.
   

3. Dial the required number.
   

4. When a headset is used, replace the handset in its cradle after the number has been dialled. To clear the line, remove the headset plug.
   

4. SHARED SERVICE LINES

TXS Working

1. Check, as described in par 2, that the line is not in use.
   

2. If the line is not in use, release the transmitter CUT-OFF button.
   

3. Connect an earth to one leg of the line. The earth is now sent to the exchange on both wires because of the telephone loop. The "X" subscribers calling equipment is brought into use.
   

4. Remove the earth connection and dial the number required.

TXE Working

1. Check, as described in par 2, that the line is not in use.
   

2. If the line is not in use, release the transmitter CUT-OFF button.
   

3. Connect an earth to one terminal of the telephone. The earth is now sent to the exchange on both wires because of the telephone loop.
   

4. Dial 1 or momentarily depress the cradle switch, after which dial tone should be heard.
   

5. Remove the earth connection and dial the required number.

TXK Working

1. Check, as described in par 2, that the line is not in use.
   

2. If the line is not in use, replace the handset.
   

3. Connect an earth to one leg of the pair.
   

4. Lift the handset and remove the earth connection, and dial the number required.

5. LOCAL BATTERY WORKING
When communication is required between working parties i.e. two Telephones No. 704 are in circuit, proceed as follows:-

1. Set the three-position slider switch to the LB position; the internal battery is now in circuit.
   

2. Connect the telephone to the line.
   

3. Push the slider switch to the RING position to call the other station.
   

4. To reduce battery drain arrange with other party which battery is to be used in circuit (see par 6)
   

5. Always replace the handset in its cradle after use to conserve the battery and to receive incoming calls.

6. BATTERY DRAIN
When the headset is plugged in and the three-position slider switch is in the LB position, there is a continuous current drain from the internal battery. To conserve the battery when the headset is in constant use, the following points should be observed:-

1. It is only necessary for one internal battery to be in circuit; one telephone should have its slider switch in the LB (battery in circuit) position and the other telephone should be switched to the CE (battery out of circuit) position.
   

2. Always remove the headset plug when the telephone is not being used and ensure that the weather-proof cap that covers the headset jack is in position.

7. CIRCUIT SECURITY
Attention is particularly drawn to the fact that customers' telephone lines may at times carry data signals. Therefore, before interrupting any cable pair, it is ESSENTIAL to check with amplifier No. 109B and Probe No. 5 that the circuit is not operating in the data mode. Data transmission can be recognised either by one or more interrupted tones (similar to multi-channel VF telegraph signals) or by a continuous or periodic 'rushing' sound. In any event extreme care should be taken to avoid interrupting service.

8. MAINTENANCE
To remove the battery (three Cells, Dry, R20PF) unscrew the cap on the side of the instrument case.

When replacing the cells, check that they are inserted correctly in series.

Make periodic battery check to ensure that the cells are in good condition and not leaking. The cells must be changed at 3 month intervals, to prevent incorrect operation of the ringing circuit.

When replacing faulty apparatus, use the following items:-

1. Telephone - Telephone No. 704
2. Headset - Headset No. 1
3. Headset cord - Plug No. 420 with Cord, Inst, No. 14/77AB, 54 in
4. Battery - Three Cells, Dry, R20 PF