The EF73 from 1950 is a screened amplifier pentode for voltage amplification of low level signals. With its high mutual conductance it could be used as a wideband amplifier.
Miniature valve were constructed with end micas as larger valves but the assembly work was more precise and Mullard had a special assembly section dedicated to the hand assembly of these tiny devices.
The three grids can be seen through the envelope where the anode is of reduced section.
A close-up of the grids. They are all formed by sealing the wire to the support by notching the support and then using a peening roller to press the displaced metal over the wire.
The cathode is a rectangular box.
The intricate assembly can be seen.
The thin glass tube envelope is 10 mm in diameter, and excluding the B8D base leads is 36 mm tall.
References: Data-sheet & 1040 Type EF73 was first introduced in 1950. See also1950 adverts.
