BELL No. 57
Trembler bell for preliminary signal and special cases in Post Office buildings.  The Bell is similar in construction to the Bell No. 44.

The Mark 1 is wooden cased whilst the Mark 2 has a plastic casing.

The Mark 2 was introduced circa 1957.

Bell No. 57A - Twin 50ohm coils (Conductor diameter - 0.0108ins with 3460 turns).
Bell No. 57B - Twin 250ohm coils (Conductor diameter - 0.0068ins with 6000 turns).

Operating Voltage Range
Check diagram N657 as the voltage is dependent on the terminal strapping arrangement.
No. 57A - 2v to 10v (2 x 50ohm coils).
No. 57B - 10v to 50v (2 x 250ohm coils).

The bell uses a 7inch diameter wire gong (Bell-gong No. 22).

Bell No. 57B Mark 1 and Mark 2 are pictured below.

Diagram - N657.

Drawing - 90903 (Mark 2).

Specification - S2.

Early variant - wooden cased
 Later variant - plastic cased (does not include the wooden plate)



Bell No 57A




 
 
BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems
Last revised: December 28, 2025

FM