The PD500 is listed as an output valve for television line scan, but Mullard describe the PD500 as: a shunt stabiliser triode for colour television.

It would be unusual for a line scan output valve to be a triode and have a low current rating. As a regulator of the EHT voltage it makes perfect sense. Stabilised HT voltages have been used on professional display equipment such as oscilloscopes for many years.

The dissipation is high because of the very high anode voltage.

The heater, cathode and grid structure are at the bottom of the valve and lie horizontally, ie in a plane parallel to the base disc. The bright electrode is the screen and the anode is the grey cylinder connected to the top cap. A warning on the envelope says that x-rays are produced during operation, and that the valve is to be used with a shield.

Simon Pearson has first hand knowledge of the PD500 and its use in British colour television receivers. The PD500 would have been connected between the cathode of the GY501 EHT rectifier and chassis. The grid of the PD500 was connected to a servo circuit and the valve operated to keep the EHT voltage reasonably constant.

The wide glass tube envelope is 36 mm in diameter and, excluding the B9D base pins, is 102 mm tall.

 
Pin Connections

B9D	1	2	3	4	5	6	7	8	9	tc
	k	s	-	h	h	-	-	g1	-	a

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	mAa	Pdiss
	7.3	0.3	25,000	1.6	30W

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 10 June 2007 {find valves by name}