Power Tube Flashing Dissapears / 6L6GC

[plexi50]

From right to left:

I have 3 Sylvania 6L6GC power tubes. One of them lost it's getter flashing as i was watching it after trying it in amp after it tested good with no shorts on my tester

The second ones flashing was starting to fade out and i shut the amp off

The third is one i bought off ebay that has very little flashing left. It came this way. When in the amp it starts to pop intermitantly

What is the cause of the getter flashing turning clear with a white haze inside the tube?

Could my tester be bad? They all read good  B&K Dyna Quick 600. I need an excuse to buy a B&K 747

[sluckey]

The usual suspect is air inside the glass.

[plexi50]

Would a tester indicate there being air in the tube?

[FYL]

Alas, no.

[plexi50]

 

[eleventeen]

Any kind of white, powdery look is a broken glass envelope. End of story. I'm trying to think if I've ever seen a tube lose its silver getter-flash (apart from when I dropped it on the floor and the glass shattered) and I don't think so!

Such a tube might test gassy, but as well, the heater will probably overheat, burn, and open up. Let's put it this way: Few prospects remain for satisfactory operation of such a tube, even if brought to 20,000 feet.   

[plexi50]

I thought i had a nice old pair of Sylvanias.    Im going after a set of RCA 6L6GC Blackplates and do it right
Within a reasonable price anyway.