The J-38 was designed to be used with a Signal Corps radio/telegraph operator training set. The strange looking binding posts and shorting strap at the back of the key were used to connect a set of headphones to one side of the key (“tel”) and the other side of the key (“line”) to the training set.
Technical Specifications:
Power type and voltage:
No Power needed
Loudspeaker: No sound reproduction output.
Material: Various materials
Model: Standard Key J-38 – MILITARY U.S. different makers
Shape: Table model, with any shape – general.
Dimensions: (WHD)
77 x 37 x 158 mm / 3 x 1.5 x 6.2 inch
Net weight: 0.3 kg/ 10.6 oz (0.661 lb.)
This is a standard key used for Signal Corps radio/telegraph operator training. It was also used by aircraft and for base radio and telegraph lines.
The strange looking binding posts and shorting strap at the back of the key were used to connect a set of headphones to one side of the key (“tel”) and the other side of the key (“line”) to the training set. The effect was to put the key and headphones in series.
The circuit closing switch on the right side of the key was used to set the key for listening (switch closed) or sending (switch open). It was mounted on an insulated (bakelite) base and had different manufacturers (e.g. American Hardware, Lionel etc.).