The PL36 was designed as a line timebase output valve for television receivers. In 1962 it was replaced by the PL500.
The design dates to the 1950s, when sets were black and white and screen sizes of 14 - 17 inches diagonal were common. The PL36 was designed for driving the line deflection on 90° deflection angle tubes.
From a Mullard Press release in February 1956: The Mullard PL36 is an output pentode primarily designed for the line timebases of television receivers using picture tubes with a deflection angle of 90°, and 16 kV EHT. The new valve is octal based, and has a 25 V, 0.3 A heater, suitable for series operation.
The maximum positive peak voltage on the anode is 7 kV and the screen dissipation is up to 5 W.
One side of the working faces of the anode. The central flange holds the stitches and supports as well as adding extra cooling surface. The control grid has cooling fins on the tops of both copper support rods.
The anode looking along the grid axis. Although designated as a pentode the construction is as a beam tetrode with bright plates replacing the suppressor grid.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 93 mm tall.
References: Datasheet & 1040. Type PL36 was first introduced in 1955.