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
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.
Last revised: April 20, 2023