PENTODE ~ Made in Great Britain
The EF50 Vacuum Tube was originally developed by the
Phillips Corporation in 1939.
It is used in Radar receivers and other military
equipment. The Mullard Pentode valve of 1939 was also
used in many military Transceivers.
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 WW2. One
additional reason that so many existed was that they had
a short life and so were changed often.
They are 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.
During mobile or airborne service, vibration would cause
unseating of the valves. The RAF Developed a screw holder
design. This held the valve firmly in place without
making servicing difficult. Spring clips also became
available for the bases, but the screw skirt is an
excellent solution to the vibration problem.
The skirt is wider than the body of the valve and the
metal base has holes for the glass pips that surround
the short pins. The central locating spigot is hollow
and conceals the evacuation seal.
The wide glass tube envelope is 32 mm in diameter and,
excluding the B9G base pins, is 60 mm tall.
Substitutes . . . . . . . . . . . . . VR-91, 10E/92