bell with a 2.5 inch gong (Gong-Bell No. 2)..
Operating voltages and resistances:-
Bell 56A - 2-5 or 5-10 volts DC (2 x 50 ohm coils)
Bell 56B - (2 x 250 ohm coils)
Bell 56C - 10-25 or 25-60 volts DC (2 x 1000 ohm coils)
Bell 56D - 2-5 or 5-10 volts DC (2 x 50 ohm coils) - includes Bobbin
Resistance 2k ohms.
Bell 56E - (2 x 250 ohm coils) - with permanently wired FR Interference
suppression and Resistor Carbon 2.2k ohms
Internal use only.
Coloured black these bells were universally used throughout BT and many private companies.
Early versions may have a wooden base (see picture below) or metal cover. Most will be made out of plastic.
Superseded Bell No. 13.
Bell No. 56 with a wooden base
(Picture dated 1932)