Telephone for use in situations of occasional hazard from explosive or flammable mixtures


Telephone No. 266 is a table type instrument (looks like a Tele No. 702) for use with a Bell No. 69A in place of a Telephone No. 149 in suitable locations.  It includes a fingerplate fly-back mechanism with a modified Dial, Automatic No. 12.  A press button is fitted and may be used for operator recall.  When recall is required it should be provided as shown on Diagram N366.  The telephone includes a tough rubber sheathed instrument cord for connecting into the Bell No. 69A.  Overall dimensions of the telephone are 9.3in x 9.1in x 6in measured with the handset on its cradle, the weight is 12.1lb.  Telephone No. 266 is superseded by Telephone No. 702 for new work.

Telephone No. 266 Mk1
This telephone (introduced around 1958) is suitable for use on lines up to 600 ohm loop resistance.  It is fitted with an extensible handset cord (Ericsson's N 4514) and has a 160 ohm resistor in series with the A line to meet the safety requirements of the testing authority.  In consequence of this transmission is degraded by approximately 2dB as compared to that of the standard telephone circuit.  The transmission and signalling limits given in TRANSMISSION, Telephone, B 3502 should, therefore, be reduced by 250ohms T.E.R., and 160 ohms on signalling limits when this telephone is used.  This telephone will be unsuitable in some situations.

Telephone No. 266 Mk2
This telephone is suitable for use on lines up to 1000 ohm loop resistance and is fitted with a rocking armature receiver.  The transmitter and receiver caps are locked on to the handset to prevent accidental disconnection's of the circuit.  The neoprene sheathed handset cord (Ericsson's N 4521595) is protected by metallic and nylon braiding.

Bells No. 69A and 69B.
Bell No. 69A is used in conjunction with a Telephone No. 266.  It provides the terminating unit for the telephone instrument and line connection and may be used as an extension bell.  A gland is provided with the bell for terminating the telephone instrument cord.  An open ¾in conduit outlet is provided for either a conduit, M.I.C.C. or armoured cable glands as required.  Two spare plugged outlets are also provided for additional external connections if required. The bell has a single 4 in gong; its range of audibility is limited and is not equivalent to that of a Bell No. 59A.  Overall dimensions of the bell are 6¼in x 6¼in x 4in; the weight is 7 lb.

Bell No. 69B is similar to the Bell No. 69A but is the superseding item, and is used with the Telephone No. 702.  For maintenance instructions see Z 5013.  Bells No. 69A and 69B must be mounted with the hinge at the left hand side and should be mounted under cover.

Made by British Ericsson, model No. N1019X1.

Circuit diagram - N366.

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Last revised: November 20, 2021