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The RCA Type 77-A (1936)
uni-directional ribbon microphone

RCA 77-A

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.

An RCA Type 77-A with its grille removed.

An RCA Type 77-A with its grille removed.

77-A and 77-DX
A size comparison of the 77-D and the 77-A.

Mr. Dave Antler kindly provided these photos and sound file of his RCA Type 77-A ribbon microphones, which he restored and re-ribboned.

RCA 77-A
Dave Antler’s magnificently restored RCA Type 77-A ribbon microphone.

RCA 77-A
A view before restoration.

RCA 77-A

RCA 77-D? and 77-A
Dave’s 77-D and another of his restored 77-A microphones.

W9AD on the air
Dave uses one of his mics on the air at W9AD. Hear Dave’s voice as he speaks into his mic.
Photos and sound file courtesy of Mr. David M. Antler, W9AD. Visit Dave’s web site.

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):

  • Bi-Directional (B) –61 vu

  • Uni-Directional (U) –64 vu

  • Non-Directional (N) –67 vu

  • Hum Pick-up Level: –125 dbm

Dimensions and Weight:

  • Length: 11½ inches

  • Width: 3¾ inches

  • Depth: 2½ inches

  • Weight: 4½ pounds

  • Mounting: ½-inch pipe thread

Wiring diagram

RCA 77-A

RCA 77-A

RCA 77-A
A size comparison of the 74-B and the 77-A.

Polar pattern

RCA Type 77-A plate

Marketing brochure

Marketing brochure

Marketing brochure

Marketing brochure

Marketing brochure

Marketing brochure

Marketing brochure

Marketing brochureDownload the eight-page marketing brochure for this mic.

Download the Instructions for this mic.


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