The RCA Type 77-A (1936) uni-directional ribbon microphone
This is the RCA Type 77-A, forerunner of the 77-DX. Grand-daddy of the ribbon microphone, the 77-A is among the rarest of the RCA ribbon mics. Designed by Dr. Harry F. Olson, RCA’s lifelong resident audio genius during the late 20s and early 30s, the 77-A set the performance benchmarks for all RCA ribbons to follow for the next four decades. It is rumored that prototypes actually existed in 1929 and 1930; however, the 77-A wasn’t announced until 1932. It featured two vertical in-line ribbons and an acoustic labyrinth inside the case, which enabled it to be uni-directional. The 77-A is a huge microphone resembling a cannon shell with a large perforated windscreen on the top portion. It is gimballed at its center of gravity in a U-shaped fork.
A size comparison of the 77-D and the 77-A.
Mr. Dave Antler kindly provided these photos and sound sample of his RCA Type 77-A ribbon microphone, which he restored and re-ribboned.
Dave Antler’s magnificently restored RCA Type 77-A ribbon microphone.
A view before restoration.
Dave’s 77-D and another of his restored 77-A microphones.
Dave uses one of his mics on the air at W9AD.
Stan holds a fully functional Type 77-A belonging to Mr. Don King.
Design, Specifications and Technical Data
Output Impedance: 30, 150, and 250 ohms
Load Impedance: Open circuit
Effective Output Level at 1,000 Hertz (all output connections):
Bi-Directional (B) –54 dbm
Uni-Directional (U) –57 dbm
Non-Directional (N) –60 dbm
L-1, L-2, L-3 between –54 and –57 dbm
Output Level for Speech at Two Feet (all output connections):
