ALTEC 639A Multi-Pattern Ribbon Model---1938-49

The 639A was introduced in 1938 and provided broadcasters
with a microphone that could be set to various direction patterns
while maintaining high quality performance. Using a velocity
ribbon microphone in combination with a dynamic pressure
microphone,making this mic the most complete one during this
time period. The selector switch is located on the back of the
639A housing. An internal transformer provided amplification
and impedance matching for the velocity ribbon sectionIn 1941,
ALTEC began producing the 639 series with the ALTEC name on
their models. The 639A/B was nick-named the "Birdcage"
microphone.This mic has been a regular feature in elaborate
broadcasting studios including the Voice of America.

Louis Armstrong in one of his moments.