The S4VB is a screen grid valve or tetrode. It is a development of the S4V from 1929 and has a lower ra and μ than the S4VA. Probably the two types were selected on test from a single production run.
Our specimen has lost its top cap connection but visual inspection shows this was the anode contact.
The cathode is oxide coated and the screen grid has a very fine pitch and is closed at the top.
The anode is formed from two small plates mounted either side of the screening cage. The screen is much larger than the anode to afford maximum isolation.
The identification is etched into the glass as is the basic operating conditions of a four Volt heater and a maximum anode potential of 200 Volts.
One of the anode plates. The glass bead, one on each side, is for fixing the lower screening plate, shown as a circular plate at the bottom of the picture.
The control grid is attached by glass beads to the stiff rods that pass vertically through the screen and are held firmly by the screen top plate.
The balloon envelope is 49 mm in diameter and, excluding the B5 base pins, is 113 mm tall.
References: 1931 data-sheet & 1043. Type S4VB was first introduced in 1930. See also1930 adverts.
