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Thread: Is a halo the sign of a bad tube?

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    Is a halo the sign of a bad tube?

    I am going through my big box of tubes and trying to determine which tubes to keep and which to toss. Most of the tubes are probably TV tubes or old radio tubes. Please give me some tips to quickly and visually identify bad tubes. Of course I know the obvious signs. If a tube is cracked or has white fog / spot, I toss the tube. Does this white "halo" around the getter flash signify a gassy tube or tube that has lost its some vacuum? Thanks!

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    Old Timer Tom Phillips's Avatar
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    To me it just looks like the getter material doing it's normal job. There is always some residual gas that reacts with the getter material over time. Since the flash is thinnest at the edges it forms that halo effect.

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    I've had them where the halo gets bigger. Got a quad of KT88s where one tube has the creeping death.

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