The Trimphone

The outcome of these endeavours was the Telephone No. 712 or Trimphone. The (then) modern design incorporated the novel feature of dial illumination, tone calling and a unique handset. The initial four letters of the name Trimphone stand for Tone Ringer Illuminated Model. The Trimphone was designed by Martyn Rowlands.

The handset was coded Handset No. 8 and featured smaller transducers (Receiver, Inset No. 3 and Transmitter No. 15) mounted adjacent to one another in the earpiece cavity. The transmitter being coupled to the mouthpiece by an acoustic horn. The transmission circuitry was based on that of the Telephone No. 706. The Trimphone was the first in the BPO range to use a tone caller which warbled at around 2000Hz modulated by ringing current. The volume of the ringer gradually built up over the first few cycles of ringing current. There is a volume control in the base of the telephone with LOUD, MEDIUM and SOFT settings. Some people were able to mimic the sound of the tone ringer by simultaneously whistling and wobbling their lips... a vulgar habit which should be frowned upon.

Production of the new telephone commenced in 1965, and an initial quantity of 1000 was offered to customers on a selective trial basis. it then became freely available, at extra rental cost, with a choice of three two-tone colour schemes: Grey-white, Grey-Green and two-tone blue. The hollow handset led to some embarrassing results when customers attempted to cover the mouthpiece by hand in order to make a confidential aside - the sound was still transmitted inside the handset!

Another problem with the dial version of the Trimphone was its light weight, 0.8kg compared with 1.4kg for the 700-type and 2.6kg for the 300-type telephone. This led to the complaint that on slippery surfaces the telephone turned and slid whilst dialling.

There was also some concern about the luminescent dial which glowed green in the dark. Although the radioactivity was equivalent only to that given off by a wristwatch it was felt wise to withdraw this facility as public concern over radioactivity grew. An improved version, the Telephone No. 722 , was introduced in 1971. This had the same outward appearance as the original, Telephone No. 712, but had the improved transmission circuitry of the Telephone No. 746 .

The First Keypad Trimphones
The first keypad version of the Trimphone appeared in 1977 - somewhat delayed by the problem of packaging the signalling electronics into the small volume of the Trimphone. The problem was alleviated by marginally increasing the height of the case compared to the dial version. The first design of keypad Trimphone to achieve large-scale production was the SC version (Telephone No. 766); this design incorporates relays, but no batteries are needed. Subsequent designs have eased the packaging problems further by eliminating the relays and introducing transistor pulsing. An MF4 (Touch-tone) design had to await the development of an integrated circuit to replace the bulky coils and capacitors otherwise needed. This was introduced in 1979 (Telephone No. 786).

The Deltaphone
The next incarnation of the Trimphone was the Deltaphone. This should really be later in this document but the notes have been included here to for continuity. By 1980 Trimphones had been around for some 15 years and needed revamping for the new era of competition. STC gave Trimphones this new lease of life by renaming the dial version as the 'Deltaphone' and the MF version as the 'Deltaphone Deluxe'. The transformation was tastefully completed by cladding these unfortunate instruments in leather. Mid-brown for the Deltaphone and a choice of Red or Green for the Deluxe model.

The Phoenixphone
The final incarnation (or rather reincarnation) of the Trimphone was a collection of alternative colour range Trimphones. These were the first part of a series of telephones known as 'Phoenixphones' and this first set was called the 'Snowdon Collection' and appeared around 1982 . Six two-tone colour combinations were chosen 'by leading design consultants' and were available in both dial and press-button versions. It is believed that Lord Snowdon had a part in these colour choices...

Olive Green Beige
Dark Orange Orange
Dark Red Red
Black Grey
Light Green Mid Green
Brown Cream


Dark Red/RedBrown/Cream

The telephones were refurbished (or rose from the ashes! hence the Phoenix association?) and were fitted with the then new PSTN cords. No rental option was available only outright sale at £35 for the dial version and £46 for the Press-button model (both prices include VAT. The sales literature pictured a press-button Phoenixphone languishing on a rush table mat with a scallop shell (ash tray), flip-up photo album and dried plant. Was this taken in Lord Snowdon's front hallway?

The Trimphone - conclusion.....
The Trimphone has been with us in one form or another for some thirty years now, and although it is unusual to see one in use these days there are still quite a few around... in fact Trimphones are still seen for sale either new or refurbished in some telephone shops at the time of writing! (1995).

Despite the complaints in the early days about it slipping whilst dialling the Trimphone has become one of the icons of British telephone design and has surely earned the right to be in any discerning telephone collection!

Most of the Trimphone notes were gratefully obtained from IBTEJ V5 p263, IPOEEJ V58 p8, IPOEEJ V74 p239 & BPO sales literature.

The Phoenixphone
As mentioned previously in the notes for the Trimphone there was a series of telephones known as Phoenixphones which were available only for an outright sale from telephone shops. The first Phoenixphones were Trimphones (Telephone No.  8722G's) already described which became available around 1982. 1 have also been told of two other issues - the second in the series were Telephones No. 8756 (SC versions of the Telephone No. 746) which were available in the following colours Pampas/Primrose/Lime/Mushroom/White.

Type Codes:-
Some instruments are marked (for example):-
              706F, 746F, 706L, 746L, 706R, 746R etc..,

   The suffix letters F, L & R have the following meanings:-
   F - All Figure dial or Dial Surround
   L - Figures & Letters on dial Surround
   R - Recall button fitted

   Other suffix letters exist. I hope to add them later!

87xx Series Telephones
Some telephones in the 7xx series were issued as low impedance versions with a PSTN type lead.  The type number for these instruments was the same as the original instrument prefixed by an '8'.  Thus a Telephone No. 8746 is a modern version of the Telephone No. 746.

Line Cord Connections
Line cord connections to a standard Tele 706/746 are as follows:-
       Red - T8 , White - T1 8, Blue - T5 , Green - T4
       straps T5-T6 , T8-T9 , Tl6-Tl7-Tl8-Tl9
Note: this is for the original 4 way lead.


Further Reading :-
Tele 706 - IPOEEJ Vol 52 page 1
Tele 712 - IPOEEJ Vol 58 page 8
Tele 776 - IPOEEJ Vol 68 page 118
'Standardisation and Control of Colour for the 700 Type Telephone' IPOEEJ Vol 56 p247
'Customer Apparatus' (1956-1981) - IPOEEJ Vol 74 page 235

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Last revised: April 21, 2023