The Hivac PX230SW is a battery output triode from 1936. This exhibit has lost the identification through the ink being smudged. The identification cam from the box it arrived in.
The front to back dimension is small.
Face view showing that the filament passes through the grid six times. The tops of the three filament loops are held in hooks at the ends of helical springs.
A closer view with a little enhancement.
The classic envelope is 39 mm in diameter, and excluding the B4 base pins is 108 mm tall.
Reference: Data. Type PX230SW was first introduced in 1936. See also1936 adverts.
