TELEPHONE No. 786 & 8786

Basic network, low send level, push button Trimphone for use on MF signalling systems.

Based on the Telephone No.2/722 Mark 2 except that a 12 button push button unit and a line powered oscillator replaces the rotary dial.

No recall switch is fitted as standard except on the Telephone No. 8786RR).  The oscillator generates MF4 tones and is unregulated, i.e. the level of signalling tones is essentially independent of line current.  During signalling the telephone transmission circuit is either shorted out or disconnected such that the signal tones are not distorted by the transmission circuit.  However, the receiver shall be a.c. coupled such that a Confidence Tone is returned.  The telephone is suitable for connection to the public and private networks.

Note the front of the casing is much higher than an ordinary Trimphone, because of the size of the circuit board for the keypad.

Mark 2 versions are fitted with Terminal 19A linked to 19B, but do not have a white wire to Terminal 19B.

It is important on Mark 2 versions, when refitting the cover, to locate the cover over the push-buttons first and then ease the cover forward to locate the case into the front lugs in the base.

Mark 4 versions are not fitted with a link between Terminals 19A and 19B, and instead have a white wire connected to Terminal 19B.

The LD Press button version is Telephone No. 766.

Introduced in 1977.

Telephone No. 8786
Introduced in 1982, the Telephone No. 8786 was a Telephone No. 786 modified to work on the Plug and Sockets system.  It was fitted with a Resistor No. 91 EJ 3K3 and a Cord Connecting No. 4/504 Light Grey, 3000mm.  The Gas Discharge Tube (Protector 11A) was also omitted.

The Telephone No. 8786RR was fitted with a Timed Break Recall button (Register Recall).  The telephone is fitted with a Kit-CP100, which is a small circuit board and whose use and circuit diagrams are covered in Specification S1376.

Circuit diagram - N886 (Telephone No. 786) and N8886 (Telephone No. 8786).

Specification - S1289, S1340, S1376 and S1486 (Telephone No. 8786).

How to wire the Telephone No. 786 to make it work on UK Plug and Socket

Additional Information
Model Mark Blue Grey Green PBU Introduced Remarks
Telephone 786 Mk 1 y y y 52A/1 8/76 STC - was 1/766
  Mk 2 y y y 52B/1 1/80 STC - was 1/766 (cost reduced)
  Mk 3 y y y 52A/2 10/78 GEC - was 2/766
  Mk 4 y y y 52A/3 1/79 PYE - was 3/766
  Mk 5 y y y 52C/1 8/79 STC - was 4/766
  Mk 6 y y y 52B/2 2/81 GEC
  Mk 7 y y y 52B/3   PYE/TMC
  Mk 8 y y y 52A/4   PLESSEY
  Mk 9 y y y 52A/5   BTF
Telephone 8786 Mk 1 y y y 7A   GEC
  Mk 2 y y y 54A/1   STC
  Mk 3 y y y 54A/4   PTL
  Mk 4 y y y 12A   PYE-TMC
  Mk 5 y y y 54A/1   GEC
  Mk 6 y y y 54A/3   TMC
Telephone 8786RR Mk 1 y y y 7A   GEC
  Mk 2 y y y 54A/1   STC
  Mk 3 y y y 54A/4   PTL
  Mk 4 y y y 12A   PYE-TMC
  Mk 5 y y y 54A/1   GEC
  Mk 6 y y y 54A/3   TMC



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

Last revised: April 20, 2023