The EY500A is a colour television efficiency diode. It is the PY500A with a 6.3 Volt heater for AC sets using a mains transformer. It would probably be found in colour monitors that would connect to other equipment. In professional applications a non-isolated chassis would be a hazard.
Thanks to Jonathan Marsh for the image.
The wide glass tube envelope is 30 mm in diameter, and excluding the B9D base pins is 105 mm tall.
Reference: Datasheet. Type EY500A was first introduced in 1968.
Absolute Maximum Operating Conditions¶
Updated February 20, 2013. shape:wide.glass.tube construction:all.glass type:rectifier.hw age:1960.1975 base:b9d heater:6.3v pins:9 pin:1. pin:2. pin:3. pin:4. pin:5. pin:6. pin:7. pin:8. pin:9. pin:tc.