Bunnell duplex telegraph relay

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 relay is a model from the early 20th century and was designed for duplex lines that could carry two messages simultaneously on the same wire. The unit bears an inspection stamp "N.Y.R.S. 9 24" indicating that it was serviced at Western Union's New York Repair Shop in September 1924.
Currently not on view
Object Name
telegraph relay
duplex telegraph relay
date made
ca 1920
J. H. Bunnell & Co.
J. H. Bunnell
Physical Description
wood (overall material)
brass (overall material)
steel (overall material)
iron (overall material)
plastic (overall material)
overall: 4 in x 8 1/4 in x 4 3/4 in; 10.16 cm x 20.955 cm x 12.065 cm
ID Number
catalog number
accession number
collector/donor number
See more items in
Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History, Kenneth E. Behring Center


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