The PL508 was designed for operation as a frame timebase output valve in 1960s colour television receivers. The PL508 had to be capable of driving the convergence coils required by the early shadow mask tubes as well as the frame coils on the wide neck tubes.
The PL508 was used in the design of the Decca Bradford television chassis.
It can withstand a positive surge of 2,500 Volts, and the heater is designed for use in a 300 mA chain. The low anode voltage is also aimed at the universal set without a mains transformer.
The PL508 is also rated for audio use and can deliver 12 Watts in single ended service. The ra value given is from the original Mullard data. Type EL508 is electrically the same but with a 6.3 Volt heater.
The stitched anode has the central flange in the middle of the active face. At the ends, as seen here, the anode has holes present through which the beam plates and inner grids can be glimpsed.
Only the outside of the anode plate is blackened. The inside is left bright as unwanted heat needs to be removed from the inner areas and not radiated back into them.
The wide glass envelope is 28 mm in diameter and, excluding the B9D base pins, is 71 mm tall.
References: Datasheet & 3002. Type PL508 was first introduced in 1967.