Early D-104 mikes used a 1' thick case, a large ID tag, and holes for 'ring & spring' mounts. Introduced in 1933, the Astatic model D-104 became known for its high frequency response that contributed to better communications audio quality. Many players modify them by putting in Shure Controlled Magnetic Transducers after the original elements fail. The Jt-30 was used by, Little Walter, James CottonBig Walter Horton, Junior Wells, Carey Bell, George 'Harmonica' Smith, William Clarke, Gary Primich, Dennis GruenlingKim Wilson and countless others. It was lightweight, cupped in the hands easily and distorted the sound when run through a Tube Amplifier. The Jt-30 is still popular among harmonica players. Both microphones were discontinued in 2013 marking an end of production for the Jt-30 after 74 years.

The Astatic Jt-30 Roadhouse was the same as the Blues blaster except with a different connector. Later versions of the Blues Blaster used a Japanese element. The Blues Blaster elements were Astatic MC-151 Crystal elements until 2001. In 1999 Hohner bought the molds to the Jt-30 shell and Astatic's very last batch of crystal elements and it was sold as the Hohner 1490 Blues Blaster. Production of the mic continued in different versions such as the JT-30VC and the CAD HM-50 that were marketed to harmonica players before being discontinued in 1999. It is one of the most popular microphones for blues harp players. There were many variations in different colors such as the Jt-30-C, W-30, 31, Jt-31, Jt-40, Jt-50, and Model A. The original Astatic model JT-30 was introduced in late 1939. Astatic also manufactured bullet style microphones, which are extremely popular among harmonica players.

Astatic serial numbers