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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 sample of his RCA Type 77-A ribbon microphone, 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.


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 brochure

Download the eight-page marketing brochure for this mic.


Download the Instructions for this mic.

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