Undoubtedly, in its category, the 5R4GY was and is among the best rectifier valves ever produced. In particular this FIVRE, genuine produced in Italy for military supply (code "21 ST") and therefore with a high standard of selection and quality; they are admirable! Absolutely flawless workmanship with large dark gray plates, mica locking on top and spring suspended filament. Highly recommended for power supply stages in Audio circuits.
EQUIVALENT: 5R4 = CV517 = 5R4G = 5R4GYA = 5R4GYB = 5R4WGY = CV684 = 5R4GYS - REPLACEABLE: 274A and B