The PL504 is a purpose designed television pentode line output valve. It was introduced as a replacement for the PL500. The peak anode voltage is quoted as 7,000 Volts and shows why the line output stage of a television receiver was the last consumer electronics product to remain a valve. The CRT excepted of course.
TV line output valves found their way into amateur radio transmitters for service at HF (up to 30 MHz) because of their peak voltage characteristics and relatively high current capability.
In a television receiver the line output stage was run at, or close to, the valve's maximum ratings. The discolouration inside the glass testifies to the hard live this valve has had.
The rectangular cathode and heat radiating fins on the control grid supports. The beam plate can be seen inside the notched anode.
The base components. The base would be formed with the internal leads bent to the correct shape. The assembly operator would then spot weld the pre-formed electrode system to the ends of the base wires.
The wide glass tube envelope is 28 mm in diameter, and excluding the B9D base pins, is 90 mm tall.
References: Data-sheet & 1040. Type PL504 was first introduced in 1961.