This is a Bell Number 56C used by the GPO, Post Office and BT. I saw this on an auction site and couldn’t resist buying it. I’m not sure what I’m going top use it for but it will be wired up to something or other before long.
The bell has two 1000 ohm coils and runs from 10-25 or 25-60 volts DC. Apparently, the coils should to connected in series when the operating current is obtained from the Exchange Line, and in parallel when the operating current is obtained from local primary cells.