The Pen4VA was, eventually, the Mullard answer to the landmark Mazda AC/Pen of 1930 for audio output within AC mains sets. Following a series of rather less successful attempts to make indirectly-heated output pentodes (Pen20) the successful but obsolescent Pen4BA was introduced with a B7 base cap. But B5 versions were supplied as replacements for its less successful predecessor the Type Pen4V. These were designated Pen4VA (5).
This exhibit is 56 mm in diameter whereas the post war version is only 42 mm in diameter.
The screw side cap is missing and the stud can be seen on the left of the base cap. The control grid is wound on copper supports and at the top is a generous heat sink.
The cathode tube is a flattened oval. The inner grids pass flat across the cathode. The suppressor grid is a little more curved.
Another view of the control grid heat sink. Note also the metal sleeves over the lower part of the copper support rods. The connecting wire is spot welded to these sleeves.
The top mica. The fingers holding the mica to the top shoulder of the envelope can clearly be seen as can the square section of the control grid heat sink.
The classic envelope is 56 mm in diameter, and excluding the B5 base pins, is 122 mm tall.
References: Private communication & 1040. Type Pen4VA was first introduced in 1933. See also1933 adverts.
