Tube replacement

[larcenasb]

Thanks, Paul! Cheers!

[BJK]

Super helpful, all. Thank you!

To the quote below. I would say mine doesn't "not look like that." I would describe it as a black-ish (almost chared) effect, with a withering of the chrome. I can post a pic comparing the different tubes. (Same thing is happening to one of the pre-tubes on my stereomor.)

I guess my question now, is what _does_ cause that to happen. Even if it's just normal, curious to understand what's going on in general.

BJK here is a photo of a tube that sucked air. Cloudy grey color, nothing shiny. It sounded fine for a few minutes but as it heated up there was scratching from the channel as the tube began to really glow, the whole thing bright orange as I reached for the off switch.
Karl

[BJK]

Here's a pic with the two different tubes. You can see the "coloring" of the on eon the right is darker/blacker, and starting to diminish.

[Paul Birkeland]

I have pulled brand new tubes out of sealed factory packaging that looked identical to the tube on the right.  If this is visually bothersome, you can purchase a new pair of tubes, but there's nothing about that photo that is cause for alarm.

[mcandmar]

Nothing wrong with those tubes. Go look at an RCA cleartop, they have a teeny tiny bit of getter material, yet they are one of the nicest 12AU7s.