TELEPHONE No. 77
Wall telephone used in Automatic exchange areas served by Siemens systems.
It was introduced when the first Siemens Brothers & Co. exchanges were brought into service, which was in 1918 (Grimsby), Stockport (1919) and Southampton (1923). It was also used on the Siemens RAX at Ramsey (Hunts.) in 1921 as well as an exchange called Hurley.
There were no Siemens Brothers & Co. public exchanges in Britain before the Great War. The Siemens Brothers works in Woolwich had an automatic PABX but this almost certainly used German Siemens telephones with monster "half moon" type dials.
The Mark 234 differed from Mark 235 as the Mark 234 had the terminals R and TR omitted.
Made by Siemens Brothers and thought to be introduced around 1916 as a Siemens picture of that date depicts the set.
This telephone had a high failure rate when in service and this is generally attributed to the capacitor wire being terminated at the junction of the dial off normal spring and the impulse spring. A high resistance fault on the impulse springs would result in failure of the bell circuit. The Telephone No. 105 is identical to the Telephone No. 77 except that the capacitor wire has been repositioned.
Superseded by Telephone No. 121S in 1928.
The table equivalent is the Telephone No. 82.
Telephone includes (1928):-
Desk No. 4 to be requisitioned separately when required.
Circuit diagram - N177.
Last revised: February 07, 2023