These pictures are of an STC prototype Trimphone, which is undated.  This is a prototype of the GPO Telephone No. 712 but is the number 66 the date, as the three hole casing was superseded by a single case fixing in 1966.

The first trial versions of the Trimphone (1965) were all two-tone grey.  The following year, two-tone blue, and green/brown were added.

The numbers on the base of the telephone below identify it as a Field Trial Trimphone:-

The numbers on the base are identified as follows:-

First Line
66-LAU-60 - This is an STC code that identifies it as a 712 Mark 1 or 2.

AAB - The first letter can be 'A' or 'G'. It gives the climate rating of the phone. 'A' is for UK use and 'G' is for tropical climates.  The second letter may refer to the type of dial.  The third letter is for the colour:-

A - Grey-white
B - Grey-blue
C - Grey-green

Second Line
S(W)2091 - Is the GPO specification number which identifies the telephone as a Mark II.

Third line
712L  - Is the GPO designation number with the L denoting that it has a dial with Letters.
TCE/67/2 - TCE being the GPO factory code for STC at Enniskillen, N. Ireland, made in 1967 and a Mark II.

Click here for GPO Trimphone history

STC prototype telephones


BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems

Last revised: September 14, 2022