RS-012
From left to right:
“Horseshoe” 7A Sounder. The copper plate when rotated pushes down the armature so that the magnetic circuit is completed while the sounder is not in use. Presumably made by Western Electric.
Western Electric “Main Line Sounder 15B” following the “Foote-Pierson” Patent of 1917.
Unidentified sounder with aluminium arm. The tension of the arm is controlled by means of a thread wound in the shaft and attached to the arm spring.