Power diode for use as a half-wave B+ rectifier. Originally intended for color-TV damper-diode service. 
The EY500A features very slow warmup (30 seconds typically), making it an excellent, rugged power-on delay device for audio amplifiers. Its warm-up time is longer than that of common rectifier tubes (such as 5AR4, GZ34), and it is lower in cost than electronic delay relays.
Its high pulse current capability gives sound quality which is superior to commonly-used rectifier tubes.

Uf = 6,3V
If = 2,1A

Ia = 440mA

Tube socket : Magnoval
Topcap : TOPXS