
Variable air condenser type 239J
Maker - 1983.046.002
General Radio was founded in Cambridge in 1915 by Melville Eastham and four other investors to manufacture radio measuring instruments and parts. Initially, the company focused on transmitting and receiving components and precision measuring instruments, as well as a few complete receiving sets. During the First World War, the company's business greatly increased. One of their products - a precision variable condenser - was used by Major Edwin H. Armstrong to tune his first superheterodyne receiver. After the war, they increased their focus on the development of precision measuring instruments, and during the radio boom of the 1920s, manufacturers turned them for the instruments needed to make radio receivers. By 1924, General Radio began its decades of dominance of the high-end instrument market. During the time, the company introduced a host of unique instruments, including the first commercially available oscilloscope. Two products developed in the 1930s found major uses during World War II: the Variac variable autotransformer and the Strobotac, the first commercial strobe light. During the cold war years, the company continued to develop new instruments and to expand. In the 1950s, they built a new manufacturing plant in West Concord, MA, and eventually consolidated operations there, closing the Cambridge plant. The company later moved to Lexington, MA, and in 1975, they changed their name to GenRad Corporation.
Maker - 1983.046.002
Maker - 1983.070.005
Maker - 1983.088.015