The PV30 is a full-wave rectifier with a series-type heater apparently for AC/DC use seems which at first sight appears to be unlikely. However, this is one of a small number of types which were intended for use in voltage doubler rectifier circuits (AC only!) in which around 200 VDC could be obtained from 110 VAC mains without using a mains transformer. Alternatively the pair of rectifiers can be run in parallel for greater current output - 60 mA per section.
The PV30S differs in having the Ct8 side contact base as does the CY2 - also with the same ratings.
The twin sections.
The B7 base pins.
Thanks to Mark Mallison for sending the images.
The classic envelope is 35 mm in diameter, and excluding the B7 base pins is 85 mm tall.
References: Datasheet, 1040 & 1043. Type PV30 was first introduced in 1937.