Brush Development Model BA-109 microphone. SOLD OUT.

There was little information available for this model.  This particular unit is in the original box  and is in very good condition.   Aside from some tarnish on the silver plated coax connector, and a property tag attached to the side of the body, this mic is in remarkable condition.

The body is deep red plastic, with an aluminum trim ring and mesh screen.  It has a standard 5/8" stand mount next to the coax jack.  Overall diameter is ~3.5", with a depth of 3", from screen to tip of the jack.

It sounds like an early crystal (piezo) microphone, thin, reedy with little low end.  

This from an old Brush advertisement:

• Flat frequency response 40~10,000 cps
• Nondirectional in the horizontal plane
• Output of 54db below 1 volt/dyne/cm2

Some information on the History of the Brush company from Wikipedia:

The business was founded in 1919 by Alfred L. Williams as Brush Labs to develop products that utilized piezoelectric crystals. Associates spun off the Brush Development Company in 1930 with piezoelectric phonograph pickups as its main product.^[1] 

Later it began manufacturing wire recorders, microphones, and speakers. Research for improvements to wire recorders resulted in a contract from the US National Defense Research Council during World War II. 

Post-World War II, Brush Development Company manufactured a dictation recorder in 1946,^[1] then in 1950 built the Model BL-206 and BL-216 Multichannel Oscillographs, and associated Model BL-932 DC Amplifiers. 

In 1952 Brush Development Company merged with the original Brush Labs and the Cleveland Graphite Bronze company to create Clevite. 

Audio products continued to be sold under the Brush trademark until 1960. 

The Clevite company was absorbed by Gould-National Batteries in 1969.^[1][2]