Earlier Solid Back Transmitter No. 1 Later Bakelite Transmitter No. 22 assembly

Wooden wall telephone used on CB and Auto systems.  Made from around 1924 and can be found in the 1928 GPO Rate Book.  All models are fitted with a Receiver Bell No. 1A and a Coil, Induction No. 14.

Early CB versions had a notice frame fitted under the transmitter (shown to the right) whereas later CB telephones had a dummy dial cover instead of the frame.

The dial mounting is a Mounting Dial Automatic No. 7.

Many of these telephones were converted Bellset No.1's.  On the rear of the phone one may well find the original Bellset No.1 crossed out and TELE 121 stamped nearby.

Some were converted by the BPO factories into Telephone No. 251, which are identifiable as they have a handset.

Similar to the Telephone No. 101 but with a dial fitted below the transmitter.  Because this telephone is sought after by collectors, it  is quite difficult to find.  A number of reproduction instruments have been seen, generally made up from Bellsets No. 1 or from railway omnibus circuit telephones.  Many of these telephones were later converted by the GPO into the Telephone No.  221.

Supersedes Telephone No. 105

Telephone includes (1928):-
1 x Bell No. 1A, unmounted.
1 x Coil, induction, No. 14.
1 x Condenser, M.C., No. 30.
2 x Cords, Instrument, No. 1/16E, Black, 12".
1 x Cord, Instrument, No. 222, waterproof.
1 x Dial, automatic, No. 10FA.
1 x Hook, receiver, F.
1 x Mounting dial, automatic, No. 7.
1 x Switch, receiver, No. 2.
1 x Transmitter, No. 1.
1 x Receiver, Bell, No. 1A.

Desk No. 4 to be requisitioned separately when required.

Telephone includes (1946 and 1956):-
1 x Bell No. 1A, Unmounted.
1 x Bell-gongs No. 2.
1 x Bell-gongs No. 2A oxidized.
1 x Coil, Induction, No. 18A.
1 x Condenser, M.C., No. 102.
2 x Cords, Inst., No. 1/16E, Black, 12".
1 x Cord, Inst., No. 2/22B, Brown, 33".
1 x Dial, Auto., No. 10 ... , S.S., No. 10 ... or Dummy, No.4.
1 x Hook, Receiver, F.
1 x Mounting, Dial, Auto., No. 7.
1 x Receiver, Bell, No. 1A.
1 x Switch, Receiver, No. 2.
1 x Transmitter. No. 22.

To be requisitioned separately when required:-
1 x Desk No. 4.
1 x Label No. 160.

Telephone No. 121 was the standard wall instrument and was fitted with a Dial, Auto No. 10FA (supersedes Telephone No. 105).

Telephone No. 121 Mark 2 was fitted with the "improved" Coil Induction No. 18.

Telephone No. 121B was supplied with a Dial, Auto No. 10BA for use in the Brighton Area.

Telephone No. 121L was in general use on Automatic exchanges in large areas and fitted with a Dial No. 10LA and a Label No. 43C.

Telephone No. 121S was supplied with a Dial, Auto No. 10FS and used on Siemens systems in Grimsby, Hurley, Ramsey, Southampton and Stockport areas (supersedes Telephone No. 77).

Telephone No. 121W was supplied with a Dial, Auto No. 10FW and used on S.T. & C's exchanges at Darlington and Dudley (supersedes Telephone No. 65).

Manufactured by:
GEC (who also made similar instruments for sale to their private systems customers). See GEC model K8384

On most examples the solid-back microphone originally fitted was replaced with a Bakelite moulding containing a standard carbon microphone inset (these assemblies were made by Siemens Brothers and where introduced around 1932/1933), making a telephone with its original solid back transmitter a relatively rare item.  The telephone is frequently (but not always) found fixed to a wooden backboard with a writing slope (Desk No. 4).

The Australian Post Office also used the same set - their Telephone No. 137AW and was identical to the Telephone No. 121 Mk 1.

Circuit diagram - N221 (original diagram is A.T. 1728).

Drawing No. 8642

Adjustment of Magneto bells

Collectors Information - what to look for

How to convert to Plug and Socket

See also the Telephone Efficiency Committees Report on Common Battery Area telephones.

Internal view showing later induction Coil (light yellow coil)
Internal view showing the large induction coil found on earlier sets (large round brown item)
Rear view showing GPO markings

There are two stampings shown.  The top shows the set was made by PX in 1932, whilst the lower stamping shows that the set was refurbished in the GPO factory (FNR) in 1956.

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Last revised: February 05, 2020