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In Reply to: RE: Silver flashing turned black... posted by JKT on September 22, 2015 at 21:39:38
That article is NOT correct about rainbow-colored flashing. Several years back, I bought a small lot of NOS 211 tubes. A number of them had flashing that was only about 1/10 to 1/4 the area of normal. The flashing in those tubes was very thin, somewhat see-through, and was rainbow colored starting at the edges and extending into the flashing to various degrees. Every tube with that degraded flashing produced a nasty internal arc when 1KV anode voltage was applied. They were useless in my amplifiers, and I lost a lot of money on the deal. I'm not sure the rainbow symptom affects smaller tubes the same way, but I'll never buy tubes again that look like that.
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Buy Chinese. Bury freedom.
Follow Ups:
In the last paragraph he writes:
"Let us make a blanket statement, to adequately cover the subject of tube viability: the only way to accurately determine the health of a tube is to test it electrically. Period. Anyone who discards a tube, because its getter flashing is slightly discolored, is wrong."
NOS Sylvania and Philips tubes are notorious for having "rainbow" edged getter flash. It's completely normal. And the vast majority of them test just fine.
So I think saying the article is incorrect - is not exactly correct. But proper testing is an additional way to screen out tubes with issues in many cases. Observation of the getter flash alone is not the final word on a tube's condition.
Are we still discussing power triodes like the 211? If so, I stand by what I've said. The article is wrong. To quote:
"(chalky white all over)... is the only case of a getter flash visually indicating a problem in the tube."
Absolutely untrue, and I have seen the physical, real-world evidence. You know, I only posted this experience thinking it might save someone else some grief. I lost hundreds of dollars on those tubes and felt damn stupid when it was all over. I don't want to argue about it fifteen years later.
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Buy Chinese. Bury freedom.
I was just saying that in some cases on some tubes (not necessarily a 211) some rainbowing is pretty much normal.
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