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The RCA Type 50-A
Inductor Microphone (1933)

RCA 50-A

Introduction
The Inductor Microphone is the result of re­search and development toward the production of a low-priced mic, the characteristics of which are high quality, sensi­tivity, freedom from shock excitation troubles, mini­mum response to wind effects, compactness, and ruggedness.

RCA 50-A

This microphone is a pressure-operated mic of the moving conductor type. A single 0.010-inch aluminum con­ductor is rigidly coupled to a diaphragm and located be­tween the poles of a permanent magnet with its length per­pendicular to the magnetic lines of force. The ends of the conductor are connected to a transformer that match­es the impedance of a 250 or 50 ohm line. Sound waves reaching the diaphragm vibrate the conductor with­in the magnetic field set up by the magnet. The vibration of the conductor is in accordance with the sound vibrations and, oc­curring as it does within the magnetic field, sets up a cor­responding alternating electric potential across the pri­mary of the microphone trans­former. These minute vol­tages are subsequently amplified to the power level required for broadcasting.

RCA 50-A

Quality of Response
The frequency response of the microphone is uniform over its useful operating range from 60 to 10,000 cycles. The variation of the frequency response characteristic with the direction of the incident sound is similar to that of any other pressure operated microphone of compar­able size, in that response to higher frequencies is atten­uated as the angle between the direction of the incident sound and the plane of the diaphragm is decreased.

RCA 50-A

The microphone and its transformer are enclosed within a sturdy and attractive metal case on the back of which is mounted a recessed male connector for the attach­ment of the microphone cable. The microphone case is fitted with a perforated metal front cover which serves to protect the transmitter from mechanical injury and ad­verse wind effects. This assembly is pivoted in a fork, to which is attached a threaded flange mounting by means of which the microphone may be fastened to the top of a microphone stand. A suspension mounting Type UP-4277 is also sup­plied with the microphone to permit the unit to be suspended overhead when desired.

From Radio Corporation of America Instructions for Inductor Microphone Type 50-A (MI-4030-A)
(MI-4030-B) (MI-4030-C), Publication IB-23801-3,
© Copyright 1934, RCA Victor Company, Inc.

RCA 50-A

RCA 50-A

RCA 50-A

RCA 50-A

RCA 50-A

RCA 50-A

marian_anderson

American contralto Marian Anderson

marian

By following this link, Marian Anderson can be heard per­forming Erbarme dich, mein Gott, Aria 39, from the oratorio “St. Matthew Passion” by J. S. Bach. The link will trans­port you to a photo array on YouTube with details of the April 9, 1939 Easter Sun­day concert de­scribed below. Your web browser’s BACK button can be used to return to the mic site. Duration of the aria is eight minutes.

Harold Ickes, Marian Anderson

Ms Anderson was an important figure in the struggle for African-American artists to overcome racial prejudice in the United States during the mid-twentieth century. In 1939 during the era of racial segregation, the Daughters of the American Revolution (DAR) refused to allow her to sing to an integrated audience in Constitution Hall in Washington, D.C. The incident placed Anderson in the spotlight of the international community on a level un­usual for a classical musician. With the aid of First Lady Eleanor Roosevelt and her husband President Franklin D. Roosevelt, Anderson performed a critically acclaimed open-air concert on Easter Sunday, April 9, 1939, on the Lincoln Memorial steps in the capital. The event was fea­tured in a documentary film. She sang before an inte­grated crowd of more than 75,000 people and a radio audi­ence in the millions. In the photo above, Interior Sec­retary Harold Ickes, who facilitated the concert, in­troduced Ms Anderson, saying “In this great auditorium under the sky, all of us are free. Genius, like justice, is blind. Genius draws no color lines.”

A five-minute, 40-second YouTube video of preparations for and entrance of Ms Anderson for her Easter Sunday concert during 1939. Use your web browser’s BACK button to return to this page.

Marian Anderson, Leonard Bernstein

Marian Anderson with Leonard Bernstein at Lewisohn Stadium,
New York, during June, 1947.

Marian Anderson, Leonard Bernstein

Instructions

From Decibels and Microphones, published by the Central Technical Institute,
Kansas City, Missouri. Publication date unknown; likely during the late thirties.

Eleanor Roosevelt

Mrs. Eleanor Roosevelt at radio station WOL, Washington, D.C.,
presenting a “My People” program devoted to African Americans.

Here are some gorgeous 50-A photos that were on eBay.

Here are four more eBay auction photos.
Winning bid was $1,276.51. Check out the yoke:

RCA Type 50-A

RCA Type 50-A

RCA Type 50-A

RCA Type 50-A

Billy Graham

Billy Graham

Upton Sinclair

Upton Beall Sinclair (1878-1968)

FDR

President Franklin Delano Roosevelt

Harry S Truman

President Harry S Truman

Operating Instructions cover

Download the instructions for this mic.

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