No, Class 50s had an ETH rating of 61. Most other large diesels with ETH had a rating of 66. Even class 31/4s were 66, because they were used on ECS workings of aircon stock.
50s use (as do 37/4s now) a second , small DC generator driven by the main PU- This was probably not designed at a time when 66 was needed ( higher amps)
31/4s, aka Peds and ETHELs have a big part of their power output reserved for the ETH. Still shows how effective loco hauled power is versus modern "plastic" DMUs.