TELEPHONE No. 766 & 8766

Second generation battery-less keypad Trimphone.  The first keypad version of this Trimphone appeared in 1977 (Telephone No. SA10006) - 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 (self contained - 10pps) version (Telephone No. 766); this design incorporates relays, but no batteries were required as it was powered by the exchange line.

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).  No Code "C" keypad was ever produced.

A lightning protector was also installed, sometimes on the main circuit board between terminals 8 and 19, but could also be found on the sender unit, connected to terminal 19 by a green wire.

Initially the telephone was prefixed with a number to identify the manufacturer.  i.e.  1/766.  This was discontinued in 1980 and the "Mark" numbers introduced.

1/766 - introduced 1976
2/766 - introduced 1978
3/766 - introduced 1979
4/766 - introduced 1979

Originally called the "Keypad Trimphone", the phone was later renamed "Push Button Trimphone - Self Contained".

Circuit diagram - N866 (Telephone No. 766) and N8866 (Telephone No. 8766).

Specifications - S1203 (Telephone No. 766) and S1486 (Telephone No. 8766).

Telephone No. 8766
In 1982 the Telephone No. 8766 was introduced and this fitted with high impedance bell ringer and a new style Plug and Socket cord (Cord Connecting No. 4/504 3000mm).  This telephone was effectively a recycled Telephone No. 766.

The Deltaphone
The next incarnation of the Trimphone was the Deltaphone.
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.

Telephone No. 766 Green

Telephone No. 766 Grey

The Phoenixphone
The final incarnation (or rather reincarnation) of the Trimphone was a collection of alternative colour range Trimphones introduced as part of the Phoenix Phone Scheme.  These were the first part of a series of telephones known as 'Phoenixphones' and this first set was called the 'Snowdon Collection' and appeared in 1982 .  Six two-tone colour combinations were chosen 'by leading design consultants' and were available in both dial and press-button versions.  I believe that Lord Snowdon had a part in these colour choices...                                t8766br1.jpg (16837 bytes)



Olive Green


Dark Orange


Dark Red




Light Green

Mid Green



The telephones were refurbished (or rose from the ashes! hence the Phoenix association?) and were fitted with the then new PSTN cords and numbered Telephone No. 8766 (Mark 9 variants).  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?

All Phoenixphones had high impedance bells and a PSTN style cords.  It is believed that they were made primarily from refurbished parts, although the cases must have been new as they were in colours not previously available.

Click here for Phoenixphone colours

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Click to hear a Trimphone warbler

You may have seen the recent press announcement that a product trial for a new SC Keypad Trimphone is to start in the London Telephone Region (LTR).  As its name suggests this is a Trimphone with the dial replaced by a keypad.  This has produced an attractive, modern looking telephone which will be initially available in one colour - Trimphone grey.  It can be on both shared and exclusive exchange lines, on direct extensions from PBXs and on the same popular plan arrangements as the ordinary Trimphone.

Previous trials of self-contained Keyphones have shown there is a promising market in the residential sector.  In response to this demand we are trying the SC Keypad Trimphone which as a light weight, portable instrument is particularly suitable for residential situations.  The keypad will also add to the instruments stability.

The Keypad Trimphone represents a major technological advance because it has no battery.  For the technically minded - power for the circuitry behind the keypad is provided by a capacitor which is charged from the line and provides a continuous current during the make/break pulses.  If this technique proves successful it is hoped to eventually introduce it to other SC Keyphones and remove the need to provide batteries with them.

A limited quantity of these instruments have been bought and the first 200 are being placed on three months free trial with selected customers in LTR South and South West Areas.  This is to allow us to make an initial study of their reliability and acceptability.  Given their satisfactory performance in the product trial, it is hoped to test market about two thousand of these telephones with new and existing customers at an additional rental of £3.35 it is hoped per quarter and with a £5 connection charge.

New Product Bulletin 1/74

3 Internal
Issue 3, June 78

Push-Button Trimphone

This Instruction describes the 10 pulses per second battery less Push-Button Trimphone which is based on the Telephone No. 2/722.


  • The Telephone No. 1/766 differs from the Telephone No. 2/722 in that a push-button unit (pbu) replaces the dial.  A recess is provided to take the customer's number label.

  • The telephone has an electronic circuit for receiving and pulsing out digits.  This circuit takes sufficient energy for operation from the line during imputing.

  • The transmission circuit is similar to that shown on Diagram N822 for the Telephone No. 2/722.  The dial off-normal contacts across the transmitter and receiver are replaced by relay contacts on the Send Unit.

  • A lightning protector is connected between terminals T8 and T19.  On no account should this component be removed.

The Push-Button Trimphone accepts the same add-on units and gives all the facilities (excepting Subscriber Controlled Group Transfer) as the Telephone No. 2/722 (see TI C3 B1015).

The Telephone No. 1/766 is available in two colours:-
(i) Trimphone Grey (Base off-white and Handset light grey).
(ii) Blue (Base light blue and Handset dark blue).

Item codes are 410445 and 410476 respectively.

Diagram N 866 covers the telephone as supplied. Plan installations should be wired in accordance with Diagrams N820 and N822.

The pulsing of Telephone 1/766 is identical to that of a normal dial telephone and can be tested for speed and ratio in the normal manner.  Tests should be carried out on installation to ensure the correct pulsing out of all digit buttons.

Around 1981 the Telephone No. 766 became the Telephone No. 8766 when it was fitted with high impedance bells and new style cord.

How to wire your Telephone No. 766 to make it work on Plug and Socket

Circuit diagram - N866.


Silver Jubilee Edition Prototypes
Produced by STC in 1977 but never adopted by the Post Office

The Post Office were looking to issue a commemorative telephone to celebrate the Queens Silver Jubilee in 1977.  Manufacturers were asked to submit ideas and STC offered a Push Button and a Dial Trimphone both with a white body and blue handset with a gold insignia embossed into the back of it. The Push Button version also had blue keypad buttons. The Post Office rejected STC's submission in favour of the Navy Blue Compact Telephone.  But there are a handful of the STC prototypes in the hands of collectors.



Additional Information

Tele 766      3/74Origonal
Tele 766Mk 1 yy y52A/18/76STC - was 1/766
 Mk 2 yy y52B/11/80STC - was 1/766 (cost reduced)
 Mk 3 yy y52A/210/78GEC - was 2/766
 Mk 4 yy y52A/31/79PYE - was 3/766
 Mk 5 yy y52C/18/79STC - was 4/766
 Mk 6 yy y52B/2 7/80GEC
 Mk 7 yy y52B/3 7/80PYE/TMC
 Mk 8 yy y52A/4 11/81PLESSEY
 Mk 9 yy y52A/5 1/82BTF
Tele 8766Mk 1 yy y52A/1 STC
 Mk 2 yy y52B/1 STC
 Mk 3 yy y52A/2 GEC
 Mk 4 yy y52A/3 PYE
 Mk 5 yy y52C/1 STC


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Last revised: April 20, 2023