The GY501 is a half wave rectifier, designed for EHT use in British colour television receivers.
On the envelope is a warning about X-ray emission in use. Simon Pearson has confirmed the use of both this valve and the associated PD500 shunt stabiliser. Both would have been operated within a screened environment and the metal screen was probably fitted with an interlock to prevent operation of the EHT unscreened.
From the early 1950s within television development, the EHT requirements were met from an overwinding on the line output transformer and a high voltage pulse was produced during the line flyback period. In time the valve EHT rectifiers were replaced in television designs by solid state encapsulated tripler rectifiers. The tripler would have been based on the famous Cockcroft-Walton circuit design.
The wide glass envelope is 28 mm in diameter and, excluding the B9D base pins, is 77 mm tall.
References: Datasheet & private communication.
Absolute Maximum Operating Conditions¶
Updated December23, 2012.