RCA Model 77-D Polydirectional Microphone
RCA 77-D Microphone-Front View RCA 77-D Microphone-Rear View
The RCA model 77-D (MI-4045-E) microphone was introduced in 1945, and remained in the catalog for about 10 years until it was replaced by the 77-DX.  It was one of the standards of the broadcast and recording industries, and is still widely regarded for its quality.  It is a heavy and substantial unit, measuring about 12 inches in height (including the WCAU flag).

A beautiful and classic design, its form is firmly rooted in the Art Deco Streamline style of the 1930's.  The RCA 77 series microphones have become powerful and universally recognized symbols of broadcasting, and still appear on CNN's "Larry King Live" and CBS's "Late Show with David Letterman". 

What you see on those shows, though, are hollow prop mikes, with the real work done by nearly invisible modern equipment.  Even as props, they invoke a vivid image of broadcasting's past glories, and offer, perhaps, the hope of substance where little actually exists.

As with any successful design, imitations were common, and mostly made in Japan, as can be seen here and here.

RCA 77-D Pattern Selection

The 77-D and DX microphones were advanced designs, which offered the sound engineer a variety of directional patterns (as selected by the screw slot at the rear of the unit).  Three frequency response options were also available, as selected by a switch at the bottom of the unit.

This advertisement for the RCA 44-BX and 77-D microphones appeared in the Mar.-Apr. 1954 Issue of "Broadcast News" magazine (published by RCA).  Click here or on the image for a larger version.