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POST OFFICE RELAY  TYPE B No 7938, 1920's

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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.

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