Altec "Coke Bottle" Microphone 21D Capsule & 150A Base - RARE VINTAGE

This is a Rare Vintage Altec M11 150A Tube Microphone system with the 21D capsule. This microphone is in the same league as the famous Neumann KM83, U63, KM53. It's amazing as a drum room mic / overheads and great on piano, acoustic guitars, guitar amps, certain vocalists! One of the greatest small diaphragm omnidirectional tube mics of all time!

This microphone is in excellent condition and was a collectors piece and was likely kept unused for decades. No cables or power supply box are included and as a result the mic as not been tested, hence, it is sold as is and I cannot guarantee it's working order. Given the condition I would except there would be no issue. If you are a collector, this is an extremely beautiful example one of the most famous microphones in the history.

Here’s the story of these legendary microphones:

Altec-Lansing billed its M-11 microphone system as "the mic that became a must!" when it came out around 1949. It’s capsule was an amazingly small mic for that era.

This microphone was a revolutionary development at the time because condenser mics had fallen out of favor in the 1930s. Ribbon and dynamics had taken over professional audio and many thought the condenser would never come back. This was Altec’s response at the time and it hit a home run.

More than 20 "man-years" were spent on the design of the M-11 system. The result wasn't just a "better mike" — smaller in size — but a microphone smaller in diameter than a dime that set a new standard in microphone performance.

Before this, the condenser mikes of the 1920s and 30s were big and had bulky amplifiers that had to be in close proximity to the pickup capsule. They were powered by large battery packs. The new smaller size capsule mated with the new "miniature" vacuum tubes developed during WWII made possible the return of the condenser mic.

Altec used an A/C power supply box instead of bulky battery packs. The capsule itself was 5/8ths of an inch in diameter and just a quarter inch thick. It had a sound entrance opening that was a tiny slot around the top edge of the capsule.

People referred to this mike as the "coke bottle" because of its unique and stylish shape. The small 21B capsule was mounted at the top of the slender coke bottle-shaped 150A base which contained a 6AU6 miniature vacuum tube which converted the very high impedance of the capsule to a low impedance by use of a cathode-follower circuit.  

The unit used a multi-conductor cable connected through a Cannon "P" 8-pin connector which was at the bottom of the coke bottle. The mic could be separated from the power supply by as much as 400 feet. This cable mated with the power supply box which supplied both filament and high voltage to the vacuum tube and condenser capsule.  

The power supply box also had an output cable that connected the system to the audio equipment it was to be used with. There was an optional matching transformer that plugged into the power supply box to provide a balanced output for professional audio systems.

The 21B capsule produced an extremely smooth and extended response over the entire audio range and was omnidirectional. The M-11 mike system became an instant sensation in the audio industry. It operates on the same level as the famous Neumann KM83, U63 or KM53. It is revered for drum rooms, piano, acoustic guitars, guitar amps and vocals. It was the start of the resurgence of the condenser microphones in the United States.