Quote:
Originally Posted by zombie1210
Dark as in it looks like carbon. Like it is burned. The cracks at the base are pretty obvious, as well.
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That sounds like the getter in the normal state it should be in. When a new tube is made a vacuum pump pumps out most of the air/gas in the tube but not all. So they take a strip of a highly reactive metal (like magnesium) vaporize it with high power RF which distributes it as a blotch on the inside of the glass (the RF also bakes the other tube elements to drive out gas/contaminants from them) to maximize its reactive surface area. That blotch then eats up any air/gas molecules that contact it preventing harmful gas buildup inside of the tube.
In short that carbon look is SUPPOSED to be there and is a GOOD thing/sign.