Please provide a brief history of the model 520 Green Bullet.
1949 - Model 520 introduced. High impedance (>10,000 ohms). Employed R5 element.
1953 - Model 520B introduced. Low impedance (150 to 250 ohms).
1974 - Model 520B discontinued.
1980 - Model 520 discontinued.
1980 - Model 520D introduced. High/low impedance. Employed R44 element.
1997 - Model 520D discontinued.
1997 - Model 520DX introduced. High/low impedance. New dynamic element designed to sound like the original R5 element. 5/8"-27 internal threaded hole replaced by volume control.
The shape of the microphone case was influenced by automotive headlamp housings from the 1930s.