The PL509 was one of the last TV line timebase output pentode valves to be designed. This exhibit is the 6.3 Volt version designed for parallel heater connection. This would be used for line timebase service in professional equipment where the extra cost of the mains transformer was not too much of a cost extra. These valves were designed for service in colour television receivers employing shadow mask tubes.
The normal anode voltage of 160 V is designed to be exceeded by pulses of up to 8,000 Volts and 1.4 Amps.
Radio amateurs also used such valves, known in America as 'sweep tubes' for short-wave transmitters, sometimes with the valves in parallel to increase the power available.
The control grid is wound on thick copper rods with L shaped cooling fins mounted on the top.
The anode has holes in the end wall and flanges in the centre of the working faces.
Looking into the end wall of the anode the two wire grids can be seen. The suppressor grid is in fact a set of beam forming plates.
The wide glass tube envelope is 38 mm in diameter and excluding the B9D base pins, is 116 mm tall.