Redding telegraph relay

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Telegraph relays amplified electrical signals in a telegraph line. Telegraph messages traveled as a series of electrical pulses through a wire from a transmitter to a receiver. Short pulses made a dot, slightly longer pulses a dash. The pulses faded in strength as they traveled through the wire, to the point where the incoming signal was too weak to directly operate a receiving sounder or register. A relay detected a weak signal and used a battery to strengthen the signal so that the receiver would operate.
This 1880s relay made by Jerome Redding & Co. of Boston features an unusual adjusting mechanism for the armature spring. Relays required adjustment to compensate for changing conditions on the line. Older designs used adjusting screws and springs to change the position of the coils and the sensitivity of the armature–a tricky task since the recommended armature action was about 1/32" (less than 1mm). The spring adjustment post on this relay is set on a sliding rail on the base and the entire post moves back and worth as needed.
Currently not on view
date made
Jerome Redding & Co.
Physical Description
brass (overall material)
wood (overall material)
plastic (overall material)
steel (overall material)
overall: 4 in x 9 in x 4 1/4 in; 10.16 cm x 22.86 cm x 10.795 cm
ID Number
catalog number
accession number
Credit Line
from Tufts University, Departments of Electrical Engineering and Physics
See more items in
Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History


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