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 anode is rectangular inside and has external side radiating flanges positioned at the centre of the working face where maximum heat is generated by electron bombardment. The control grid has radiating fins on the tops of the support rods.
The notch in the end of the anode shows the bright beam plate within.
The wide glass tube envelope is 28 mm in diameter, and excluding the B9D base pins, is 89 mm tall.
References: Data-sheet & 1040. Type PL504 was first introduced in 1961. See also1961 adverts.
