RCA 77-A

This forerunner to the classic and popular 77-DX is among the rarest of the RCA ribbon mics. 

It was designed by Dr. Harry Olson and set the benchmark for ribbons for decades to follow.

The 77-A was launched in 1932, although it is rumoured that proto­types were built in 1929 and 1930. The 77A featured a spiral acoustic labyrinth inside the body and two vertical in-line ribbons enabling a uni-directional polar response.

The 77-A is a huge microphone resembling a cannon shell with a large perforated windscreen on the top portion.  The example in our collection weighs a massive 4.3 kilograms and is over 33 cm high, making it the largest mic in the museum. 

Output impedance 250 ohms

Output level (10 bar input): 69 db

Directional Level: 10:1

A description of the RCA 77A at the Coutant website, including a full 8 page manual.

RCA 77A data sheet from 1936

The image of four gentlemen at the piano singing with an RCA 77-A is the from the collections of the State Library of NSW and was taken by Sam Hood in 1938.