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The RCA Type BK-1A
semi-directional pressure microphone (1952)


RCA Type BK-1A, MI-11007, on Desk Stand KS-11, MI-11008

The Type BK-1A pressure Microphone is a high-fidelity instrument of the pressure-actuated type, especially de­signed for announcing and remote pickup. Its smooth response and frequency range (60 to 10,000 cycles) make it suitable for reproducing both music and speech. It is effectively non-directional when mounted vertically and is semi-directional when mounted horizontally.

The moving element consists of a lightweight molded dia­phragm attached to an annular coil assembly which is placed within a magnetic field. Coupled to the dia­phragm is an acoustic circuit so proportioned that the diaphragm velocity remains essentially constant for a constant sound pressure from 60 to 10,000 cycles. The coil is connected to a transformer which provides output impedances of 30, 150, and 250 ohms.

When mounted vertically the BK-1A Microphone is non-directional with the higher frequencies uniformly atten­uated. When mounted horizontally, the microphone is essentially non-directional for frequencies below 2,000 cycles, and the higher frequencies are attenuated more as the angle with the perpendicular line to the dia­phragm increases. Figure 3 shows the relative direc­tional output or pickup with the microphone hori­zontally positioned.


The BK-1A Microphone is particularly recommended for broadcast announcing and remote pickup. It is a small, lightweight microphone which may be carried in the hand for interview and mobile use or used with a stand. The relatively high output level, which provides a good signal-to-noise ratio, is advantageous for remote work. When it is used in the open air, its construction makes the effect of air currents practically negligible. The micro­phone is also excellent for many studio applica­tions which require a non-directional or semi-direc­tional microphone.

Caution: Airtight joints above the foot of the BK-1A Microphone are essential to its proper operation. Use a good grade petroleum jelly to seal the joints when re-assembling after servicing.

Frequency Response

Figure 2 — Frequency Response

Polar Patterns

Figure 3 — Directional Patterns.

BK-1A Internal BK-1A Internal The RCA BK-1A The RCA BK-1A RCA Type BK-1A

Three photos above courtesy of Darrin Warner, Big D Broadcast Exchange

RCA Type BK-1A

Photo courtesy of Ron Harter

The RCA BK-1A Wiring diagram 1967 RCA catalog page President Lyndon B. Johnson

President Lyndon Baines Johnson

Brinkley, Huntley

David Brinkley and Chet Huntley

President John F. Kennedy

President John Fitzgerald Kennedy

BK-1A Instructions

Download the instructions for this mic.

This mic’s unofficial nickname is “the ice cream cone.”
For historical reference only, original price was $79.50.
Microphones on this site are not for sale.

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