Western Electric 300 B Vacuum tubes

I am going to ask what I would consider kind of a crazy question about the vacuum, because these are vacuum tubes, and my question is this: when I start up my 300 B SET-V amplifier, and I see what appears to be a vacuum, in only one of two tubes, (appearing like some sort of steam or condensation inside), is this normal? They play/sound fine …I don’t have any complaints, but I’m not used to actually being able to see a vapor inside the tube as it warms up. (Of course when you have tubes that are this expensive you tend to wonder if they are A-OK… I don’t get this experience on any of my other 300 B vacuum tubes). Maybe it’s because of their high-quality I don’t know.

has anyone had this experience as well? Thank you so much.