RCA Model 74 "Junior Velocity" Microphones
RCA Model 74 Microphone
RCA introduced the first of its ribbon velocity microphones in the early 1930's (the 44, the PB-31, the PB-90, and several others).  They were expensive, high quality units intended primarily for broadcast, film, and recording work.  They saw a market for a smaller, less expensive model for less demanding applications, and so the "Junior Velocity" microphone was developed.  It was introduced in 1935 and remained in production through the 1950's.

The earliest version, is shown above.  The paper label inside identifies it only by the "Junior Velocity" name, and by a stock number (9645), though RCA documentation lists it as the MI-4010.  This would have been the model 74, though it is not clear whether RCA officially designated it as such.

The base was made from several pieces of heavy gauge steel sheet, formed and welded together.  The RCA logos are separate pieces.  The perforated brass shell was a single unit secured by two screws at the top.   The entire microphone was finished in dark brown crackle paint.


The next version was the 74A, which used a yoke style mounting, like the larger model 44.   It was produced only in 1936 and is quite rare.  The one piece shell was replaced by a two piece affair, secured by a screw on each side.  The protective fabric lining covered the inside of the shell, affording better protection from dirt and debris.  This version was identified by the RCA Master Item number MI-4035.
RCA 74B Microphone RCA 74B Microphone
Most often seen is the model 74B.   The 74B was identified by the Master Item number MI-4036.  The bases were die cast zinc, with integral logos, and the shells were two piece affairs, secured by a screw on each side.  Two examples of the 74B are shown here.  One has a black painted base and a bright chrome shell.  The other has an umber painted base and a satin chrome shell.  The 74B was an improved design, with a shielded matching transformer, and soft rubber noise isolation bushings in the magnet support structure.

Above is a catalog entry from a circa 1937 RCA sound equipment catalog.

RCA 74-Interior Front View RCA 74-Interior Rear View

Interior of the RCA 74 microphone.


Interior of the RCA 74A microphone.

RCA 74B-Interior Front View RCA 74B-Interior Rear View

Interior of the RCA 74B microphone.