Shure Model 520D Microphone
From the 1949 Shure Brothers Catalog:
The “Green Bullet” is a new Shure Controlled Reluctance Microphone. It is a magnetic unit, especially designed to provide quality music and speech reproduction at moderate cost. The “Green Bullet” is practically immune to the effects of high temperatures and humidity. It is a rugged streamlined unit that lends itself to fine-quality low-cost installations where durability is an important factor.
The “Green Bullet” has a stability assured by unique control of the reluctance of the magnetic system. It features: high output, good response, high impedance without the need of a transformer. The “Green Bullet” has a beautiful modern metallic green flnish with a plated grille. Frequency response is 1 00 to 7000 c.p.s. Furnished with 15′ single-conductor, shielded cable.