Tone Ringing Illuminated Model..
In the mid-Sixties, style, innovation and design were all important. The Trimphone met all of these criteria: It was a modern, stylish phone and the first to have the handset placed in line with the dial, instead of at right angles.

GPO Leaflet PH1089 - Design John Ward, Photography Alan Marshall.
| EXIT | Trimphone History | GPO Trimphones | STC Deltaphones | Radiation | More Trimings |

  • Tone - The first  BPO (British Post Office) telephone to have a Tone Caller in place of a bell.
  • Ringing - Adjustable volume settings for the tone caller... off, soft, <, loud.
  • Illuminated - A radio-active dial!
  • Model - A stylish case in a choice of 3 modern colours... Two-tone Blue, Grey/Green, Grey/White.

A compromise between style and function, the Trimphone has remained the topic of conversation (literally) for well over 30 years*, since its first appearance in 1964. [* at the time of writing]

Critics disliked its tendency to slide about as you dialled a number. Others were caught out by its acoustically coupled microphone. There were reliability problems with early versions. And the heavy-handed discovered that the handset rest could easily be broken. Overall though, the Trimphone was a status symbol, stylish, sexy, sleek, and a big innovation in terms of design and appeal to the disconcerting telephone user. It boasted many special features, bringing together the best of the evolving telephone technology. The Trimphone remains a design icon of the 20th century and these pages serve as a reminder of its many incarnations...

  • In the early Sixties, a new type of dial telephone was developed for the Post Office under the British Telephone Technical Development Committee.
  • By 1964 the Standard Telephones and Cables produced Deltaphone was introduced.
  • In 1965, the Post Office named this product the Trimphone and an initial quantity of 1000 phones were released on trial into the rental market.
  • The Trimphone was given the engineering code of  Tele No.712.
  • By 1971 the new version, Tele No.722 had an improved transmission board, comparable to the standard 746 dial telephone.
  • STC's press-button (SC) Deltaphone was launched in 1973 (approx) and trialled as the Post Office's Tele No. 1/766 during 1974.
  • Tele No.786 the MF Trimphone followed in 1979 (approx).
  • In 1980, British Telecom's Special Range Telephones included, the Deltaphone & Deltaphone Deluxe.
  • Finally in 1982-The Phoenixphones which were refurbished, repackaged Trimphones.

GPO Trimphones
GPO Trimphones   
In the early Sixties, a new type of dial telephone was developed for the Post Office under the British Telephone Technical Development Committee.

"The Trimphone had a neat, stylish, lightweight handset, easy to hold and untiring on the arm for those long chats on the phone. The Trimphone was a fashion statement, not something to be hidden away. To facilitate comfortable telephoning, the Trimphone had a long stretchy (helical) matching colour line cord."

Here we take a look at the evolution of the GPO branded Trimphone in all its versions from the dial through to modern press-button...
STC Deltaphones
STC Deltaphones 
With some exceptions, contracts for the supply of telephones to the British Post Office (BPO), were placed with leading manufacturers whom also sold the products in their own right, often exporting abroad. Thus the Deltaphone as made by STC was named the Trimphone when marketed by the BPO.

Here we study STC's Deltaphones in detail. 
The Trimphone's luminous dial, was produced by a  radioactive Betalight...

The dial of the Trimphone is illuminated by means of a c-shaped sealed glass self luminescent tube coated internally with phosphor and filled with tritium gas.

"The low-energy Beta radiation energizes the fluorescent coating and is then absorbed by the glass. The secondary radiation (Bremsstrahlung) which then arises has been confirmed by both the Post Office Radiological Officer and the Radiological Protection Service to be much less than the recommended maximum for luminous wrist watches. The tube is expected to have a useful life of at least 10 years."

 [Post Office Electrical Engineers' Journal, Vol 58 Part 1 April 1965]

Listen to a ringing Trimphone.wav (0.6M)

Trimphones reborn in 2009... by Wild & Wolf

Design, images and text compiled by Light-Straw. Page last updated 7th December 2011.
With thanks to Simon Chappell, Paul Ebling, Bob Freshwater, Rob Grant, Nathan Pace and Jan Hodson. 

All logos and trade marks are the property of their respective owners and are used on the Light Straw site(s) for review only. Students and researchers are recommended to make their own independent enquiries as to the accuracy of the information contained therein.