The PL509 was one of the last TV line timebase output pentode valves to be designed. The PL519 replaced the PL509 and was pin compatible. These valves were designed for service in colour television receivers employing shadow mask tubes. The EL509 differs only in heater requirements.
The normal anode voltage of 160 Volts 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 has large radiating fins on top of the support rods. The openings in the anode at the end of the grid axis allow the two inner grids to be seen. The wires pass flat across the flat cathode faces.
The top mica has a small screen above it and the copper control grid supports can be clearly seen.
The pins are held in the hard glass foot. The main envelope is of softer glass.
The wide glass tube envelope is 38 mm in diameter and excluding the B9D base pins, is 114 mm tall.
Reference: Datasheet. Type PL509 was first introduced in 1969.