Toshiba Type A / SN-1631

From the Xaudia blog

The Toshiba 'Type A', aka model no SN-1631. It is a very close copy of the RCA 44A and its relatives. I was informed by Japanese expert Takayoshi Sumitomo that this was made under license by RCA, most likely in the post-WW2 era. Having looked carefully at the Type A and compared it to my own RCA PB144 (right), I have no reason to doubt his assertion.

Inside the microphones there are many similarities and few differences. Both use three large horseshoe magnets to provide the magnetic field, and the ribbon dimensions are very close. Perhaps the biggest difference is that the RCA uses cast pole pieces, whereas in the Japanese version they are milled. This probably reflects the tooling and machinery available at the time. Casting is an expensive process for low quantity products.

Badge on the box reads:

Type A Velocity Microphone

Model: OB-1028 Impedance: 600 Ω

No.: (blank or worn serial number field) 1952, (blank or worn month field)

Tokyo Shibaura Electric Co., Ltd.

Badge on the Microphone reads:

Velocity Microphone

Model: SN-1631 Impedance: 200 Ω

Serial No.: 1656 December, Shōwa 22 (1947)

Tokyo Shibaura Electric Co., Ltd.

A post about the Toshiba model A at the Xaudia microphone blog, which compares the microphone to an RCA PB90