GPO 712/722Trimphone

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Although it was designed and introduced in the 1960s, for many Brits this is the epitome of 1970s modernity. Inspired by the Princess model in the USA, GPO wanted their own de luxe designer phone and this lead to the development of the Trimphone, Tone Ringer Illuminated Model. Like the Princess it was small, light and had an illuminated dial. For its design help of the COID, Council for Industrial Design was enlisted, as they had been involved with the development of the 706 before. They selected Martin Rowland’s design for Standard Telephones and Cables Ltd (STC) from a number of proposals by several companies. Initially called the Deltaphone, after several field trials and design changes the Trimphone was made available to the general public in 1968. After some design changes in 1970 the designation was changed from type 712 to type 722.

It’s design was by no means appreciated by everybody and by the late 80s it was regarded as quaint relic from the 70s. Nowadays it is appreciated as a design classic.

Radio active

The early models had an illuminated dial, hence the term illuminated. This illumination was achieved by a radioactive gas. Although the level of radio activity was not dangerous, it did lead to health and safety concerns. Later models had normal dials because of this, although the name Trimphone was retained.

Unusual features

The Trimphone had some unusual design features, that make it unique. Other than being compact and light and have a dial illuminated by radioactivity, it had the handset vertically over the dial, similar to the Siemens & Halske Fg Tist 282. The plunger for the hook switch was made of clear plastic, sticking up prominently out of the housing where small plungers were the norm on more conventional telephones. This prominent plunger doubled as a carrying handle, so the subscriber could comfortably carry it around while conversing, as far as the line cord would let him of course. The handset had the transmitter and receiver, back to back, in the top of the handset. The sound was directed from the mouth piece to the receiver via a plastic tube, reminiscent of the French cornet type handset from the 1910-1920 period.  (PICTURE) It made use of a printed circuit board for its electronic components and instead of a mechanical ringer with bells, it had a tone caller, sometimes called a warbler. It was one of the very first, if not the very first, telephone in production to have a non-mechanical ringer. Although it had rubber feet, it tends to slide when the dial is operated. To remedy this problem STC developed a low torque dial, but that was never adopted by GPO.


Aside from the version with a rotary dial, there were push button variants, the Trimphone being designed with push buttons in mind from the start. It was made available in 1977 with a pulse dialing key pad as the type 766. In 1979 a touch tone (DTMF) version was introduced as the type 786.

To revamp the design a line of leather covered versions were introduced as the Deltaphones. (FOLDER SCAN).

The Phoenixphone was a version with an alternative two tone colour scheme, in several shades, one scheme being 2 tone red. These Phoenixphones were also referred to as the Snowdon range or Snowdon collection. Today a reasonably good replica is made by Wild & Wolf, which has a modern touch tone dial with the keys mounted in a circle, mimicking the old rotary dail.

In my collection

I got a grey Trimphone from a friend in the UK, as I found the model very interesting and I wanted to study one up close. But there was also a red version, as described above. Of course that was the version that I really wanted. I was able to buy the red one from a friend and fellow telephone collector, as I found that my collection of red telephones could not do without one. Perhaps in the future I will try to obtain a red push button version, but as I already have one with a dial, I will not actively search for one.

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