RCA Junior Velocity (MI-4010-A)

The Junior Velocity ribbon microphone was Introduced in the late 1930s as a lower-cost alternative to the RCA 44 series, using simpler construction and a lighter housing. It was succeeded by the 74-A and then the very popular 74-B.

The RCA data sheet for this microphone is marked 4/36, which suggests a publication date of April 1936.

The photograph of Robert Taft, Senator of Ohio in 1939 is from the Harris & Ewing collection at the US Library of Congress.

From the RCA data sheet

THE RCA JUNIOR VELOCITY MICROPHONE is an entirely new and improved high quality microphone, which, due to its remarkable performance, has been marked as one of the major improvements in the art of sound reproduction.

The new type of construction and new principle of operation based on velocity actuation, employed in this microphone, result in highly favourable directional characteristics, high sensitivity and faithfulness of response. These favourable operating characteristics in turn impart a naturalness of tone and a distinctness of speach not heretofore possible with any previous type of microphone used for public address and sound reinforcing purposes.

The usual stiff diaphragm used in all previous types of microphones is replaced in the new velocity microphone by a thin, light-weight, aluminium ribbon. This ribbon is suspended between the poles of a permanent magnet, thus eliminating the necessity of any field supply. The unique, simplified, rugged construction together with high quality performance makes the Velocity Microphone ideally suited for public address and sound reenforcing applications of all sorts.

• Frequency Range: 50 Hz - 10,000 Hz
• Impedance: 250 or 16,000 Ohms
• Average operating level: -68 dB

A post about the RCA Junior and related microphones at the Coutant Website

RCA 4010-A data sheet.