TELEPHONE No. 121


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

Wooden wall telephone used on CB and Automatic systems.  Made from around 1924 and can be found in the 1928 GPO Rate Book.  There were two variants, the Mark 234 and the later Mark 2.

All models are fitted with a Receiver, Bell No. 1A, but the Mark 234 was fitted with a Transmitter No. 1 and a Coil, Induction No. 14, whilst the Mark 2 was fitted with a Transmitter No. 22 and a Coil, Induction No. 18A.  Terminal numbering/lettering and the wire colours also differed - see tables below.

Terminal Equivalents

Telephone Strip

Mark 234 Rec Rec - L1 R E TR L2 -
Mark 2 1 2 3 4 5 6 7 8 9

Dial Strip

Mark 234 Trans Trans 1 2 3 4 5
Mark 2 1 2 3 4 5 6 7


Early CB versions had a notice frame fitted under the transmitter (shown below right and called the Frame, Notice No. 1) whereas later CB telephones had a dummy dial cover instead of the frame.  Many are seen on a backboard with a writing shelf called a Desk No. 4.

The dial mount 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.

The early type used a Transmitter No. 1 which could have Label No. 43 fitted between the speaking tube and the transmitter body.  This label advised of the Exchange name and number.  See picture above.

Superseded the Telephone No. 105

Mark 234 Telephone includes (1928 Rate Book):-
1 x Bell No. 1A, unmounted.
1 x Coil, Induction No. 14.
1 x Condenser, M.C. No. 30.
2 x Cord, 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.

Mark 2 Telephone includes (1946 and 1956 Rate Books):-
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 Cord, Instrument No. 1/16E, Black, 12".
1 x Cord, Instrument No. 2/22B, Brown, 33".
1 x Dial, Automatic No. 10 ... , S.S., No. 10 ... or Dummy, No.4.
1 x Hook, Receiver F.
1 x Mounting, Dial, Automatic 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.

Variations
Telephone No. 121 Mark 234 (aka Mark 1) was the standard wall instrument and was fitted with a Coil, Induction No. 14 and Dial, Automatic 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, Automatic No. 10BA for use in the Brighton Area.

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

Telephone No. 121S was supplied with a Dial, Automatic 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, Automatic 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

Variants:
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 which was identical to the Telephone No. 121 Mark 234.

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

Drawing No. 60490 (Mark 2).

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: August 23, 2021

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