Plate coating loss - Contamination? - Byrd69

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Plate coating loss - Contamination?

A recent post spoke about spotting on plates. Here's a tube I've saved just to show what loss can look like....likely from a contaminated surface, or oxide coating during manufacture. The other plate looks fine.
This is an RCA 12AX7. I have not tested, nor listened it to see what it does.
Any other thoughts?

Your interest may vary but the results will be same. (Byrd 2020)

I can't compete with the dead. (Buck W. 2010)

Cowards can't be heroes. (Byrd 2017)

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Edits: 02/07/15

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Topic - Plate coating loss - Contamination? - Byrd69 18:33:27 02/07/15 (6)

RE: Plate coating loss - Contamination? - unclestu 19:23:26 02/07/15 (5)

I considered that too.... - Byrd69 19:59:45 02/07/15 (4)

That's because - Frihed89 08:34:31 02/08/15 (3)

RE: That's because ....yeah yeah yeah.... - Byrd69 13:26:35 02/08/15 (2)

RE: That's because ....yeah yeah yeah.... - Frihed89 01:37:11 02/09/15 (1)

RE: That's because ....Too expensive for my data. - Byrd69 12:25:38 02/09/15 (0)

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