The 12SR7 when purchased by the American Government was called the VT-133. The valve is a double diode triode with a common cathode. It was designed for superhet receiver use where the diodes would act as signal detector and AGC detector and the triode would be the first stage audio amplifier.
The RCA logo.
The Radiotron brand name.
The thin metal tube envelope is 25 mm in diameter and, excluding the IO base pins, is 51 mm tall.
References: Datasheet, 1040 & 1043. Type VT-133 was first introduced in 1939.