This is a Signal Corps portable spark transmitter marked SCR-74-A, made by American Radio and Research Corporation (AMRAD), New York NY and Medford Mass. (Reference BC-18A.) It has the instructions and schematic in the lid, and an original paper tag attached (not filled out) with AMRAD's Medford Hillside address. This consists of an induction coil, spark gap, battery meter and telegraph key. For more details, see the link URL. Respond to artifaxbooks@yahoo.com