Vacuum Tube, Sora

FM-2A05A manufactured by Japan Radio Co., Ltd. was established as the all-purpose pentode for naval aviation in 1943.

Its performance as an all-purpose vacuum tube was excellent, and it was mechanically very solid.
However, it had mass production problems.
The Imperial Japanese Navy also demanded our company manufacture the pentodes; however, Eizaburo Nishibori, the then chief engineer (who should go on to lead the first Antarctic wintering party.), refused the demand because it was very difficult to produce them.
Instead, after labored research, he successfully developed and delivered the vacuum tube, "Sora" which possessed equal abilities to FM-2A05A and was able to be mass-produced more easily with our original procedure.