TELEPHONE No. 21

Wooden wall telephone used in CBS areas and long distance party lines.  It could also be used on Magneto circuits in connection with an externally fitted generator.

Also known as the Post Office telephone for Granular Transmitter 'C' (GTC).

Whist similar to the Telephone No. 17 and No. 19 it differs in respect to the switch hook mechanism, which is split into two sections.

There is no bell in the telephone so a external bell must be provided.

Uses a Deckert transmitter but may be converted to a transmitter inset - Transmitter No. 3.  This was fitted in a Case, Inset, Ebonite.

The telephone can also have an additional receiver fitted (Receiver, Bell D and Cord, Flexible No. 222).  This will hang on the right hand side of the telephone on a fixed hook (Arm, Bell Receiver).

The GPO Stores Rate Book 1928 & 1933 advises that this telephone was also used on Wallboards, telephone, with fire-signal, London Fire Brigade and M.F.B.

Note the oval brass number plate.  Each bell and telephone carried its inventory number for identification. Around 1907 the Post Office realised that numbering each telephone was too much effort for too little usefulness and stopped the practice.

This telephone would generally be found fitted to a Wallboard (Diagram TL276, figure 2).  A four cell Leclanché battery was also supplied.

Supersedes Telephone No. 17.

This telephone was not available in the 1946 Rate Book.

Telephone includes (1933):-
1 x Coil, Induction No. 1.
1 x Receiver, Bell No. 1A or No. 2B.
1 x Cord, Instrument No. 222.
1 x Transmitter No.3.

Circuit Diagram - N121.

Telephone No. 21
when used in conjunction with a coin box connected to a Trunk Switch Section

The above setup is used at a coin box installation where there is one Telephone No. 21 fitted at the counter and one fitted in a silence cabinet.

The counter telephone is installed as shown above and includes a 2 position switch, a 100 ohm magneto bell and a 25 ohm Trembler bell.

The Magneto bell signals incoming calls and the Trembler bell signals when the cabinet phone goes on hook.

The cabinet also has a coin box connected the telephone.

This telephone was also used when a Call Office Switchboard was installed.  It supply from 2 to 5 circuits.