sentences:  RCA Type 77-A microphone
  
  The RCA Type 77-A microphone was a simplex ("uni-directional") ribbon microphone, the forerunner of the RCA Type 77-DX microphone.The 77-A was designed Dr. Harry F. Olson in the late 1920s or early 1930s; prototypes are rumored to have existed in 1929 and 1930, but the 77-A was not announced until 1932.