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.

128x128Ag insider logo xs@2xmoose89

I've owned a 300b amp, and never saw any sort of condensation. I do think it could be a problem in the future. I would call the dealer you bought them from. That's a lot of money!

A vacuum is the absence of any vapor.  it is invisible.  I don't know what you are seeing, and maybe people familiar with this tube can tell you what it is, but I know that normal is to see noting inside but clear nothingness.


From Dennis Had:

Dave, this is completely normal No problem whatsoever. I believe the western electric website I think there’s an article about it.
Have a great day and enjoy the music 

I've not had this with my WE 300B's, but it seems a quick call or email to WE might have been useful, too; these are under a long warranty, after all. 

@moose89 What color is the 'vapor' (BTW its not actually a vapor but it is caused by molecules in the tube)? If bluish, no concern.


I would have to say it’s clear, like a mucus looking bit…for a brief bit…then poof…gone

@moose89 I’ve been doing this stuff for over 45 years. That’s a new one on me.

FWIW, usually anything other than the filament being lit and a light blue glow just on the inside of the glass when running, any ’lights’ or other phenomena inside a tube suggest a Bad Thing is about to happen or will happen soon. If you have another tube that isn’t doing this while this on is, that says to me that a Bad Thing is looming.

Yep. All good. Bluish light on the lower plate to start up the tube. After the suggestion to call WE, I was assured my tubes were A-OK. (Coby was great to talk to)