POST OFFICE RELAY TYPE B No 7938, 1920's

Used in Telegraphy to amplify the power lost on long cables, by activating a sensitive coil which moves contacts that operate equipment powered locally. Post Office Standard Relay 'B' taller version.

This relay replaced earlier forms known as 'A' having coils of 100 ohms instead of 200 and being shorter in length. Relay 'B' also having differential coils (two winding on each coil) It can be of the polarised (see item A0239) or non polarised type the polarised version (taller) has a magnet and can be neutralised as in use with the double plate sounder item A0227, provided it has double throw contacts, which means the pole or tongue 'T' held between M(mark) and S(space) contacts. The relay shown has a single throw contact. and is polarised (Has a magnet).
See item A0252 for types of telegraphy relays.

A0254