The EF50 was the ubiquitous red valve for a decade. Designed in 1938 by Philips of Eindhoven for Band I television receiver use and first released in 1939, this amplifier pentode was a general workhorse. It was extensively used in radio and radar during WWII. One additional reason that so many existed was that they had a short life and so were changed often.
he EF50 is an early all glass design as can be seen from the short pins and the metal base with centre spigot. The pins are equi-spaced around the circumference of the pin circle. Unlike the American metal valves, these have a glass envelope with a thin aluminium outer screening can.
The interesting fact for this exhibit is that this was made in America as Britain could not meet wartime demand.
The wide glass tube envelope is 33 mm in diameter and, excluding the B9G base pins, is 60 mm tall.
References: Data-sheet & 1040. Type EF50 was first introduced in 1939.