Signedfront plate: GENERAL RADIO CO. / CAMBRIDGE MASS.
Inscribedfront plate: 600 ~ / AUDIO OSCILLATOR / TYPE 213 SERIAL No 572
FunctionIt was used to generate tones of medium pitch, around 600 Hz (or 600 d.v./s).
Primary SourcesH. M. Halverson, "The Audio-Oscillator," The American Journal of Psychology 38, No. 2 (1927): 294-295.