From what I was told back in the day, thoriated filaments these days are not the thoriated filaments of old. I think it was Jack Strayer who explained that the techniques of old put the thorium deep into the filament alloy, and on the current stuff the thorium is has a much thinner penetration. On the old tubes you wanted to cook them well after sitting for any length of time, to get a new batch of thorium to migrate up to the surface. Not sure how that translates to newer thorium tubes.
As for calling this tube with a thoriated filament a 300B, it reminds me of the joke about the guy out walking his bulldog. A guy comes walking the other way with this really ugly, stubby legged dog with a huge head. As it passes by the first guy the ugly dog bites the head off the bulldog. The first guy says, s**t! what kind of dog is that?!
The second guy answers -
"Before I cut off its tail and painted it yellow it was an alligator."
RCA made a thoriated tube to compete with the WE300B in terms of linearity and sound quality in theater installations. But they didn't call it a 300B. They called it an 845.
