Spotting used valves

[Lawrence001]

I have a question please. If a valve is sold as NOS but the glass near the top is dark and smoky on the inside is it likely it had been used? I'm assuming this is coming from the heaters and possibly the electrons being emitted over time. In particular is it more likely if you have a pair, one clear and the other smoky? I'm thinking here some production processes might smoke the glass but then surely they should all be smoky? Not black but clearly darker when you hold them to the light, or against white paper.

It happened the other week off ebay and I sent it back but this time it's a private sale. I don't want to raise the issue unless it's clearly (or at least in the balance of probability) not NOS.

Once this questions been answered this thread could be used for other tips about spotting NOS (or not) valves.

Thanks

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[Ali Tait]

Do you mean separate to the getter?

[Firebottle]

I think the dark and smokey you are referring to is the getter, a chemical deposition on the inside of the glass which absorbs any remaining impurities left when the glass envelope is evacuated.
The getter can vary in size and position a lot, hence some valves can have a clear top, but the colour is usually a dark grey/silvery colour.

Well used power output valves can show brown marks, usually near the anode plates, but that is after many many hours.

It's a difficult one.

[Lawrence001]

I don't mean the shiny bit at the top, if you look in the photo you can see right through one but the glass has a brown tinge on the other one towards the top. https://uploads.tapatalk-cdn.com/20190624/632d8012e3866f1f7530a15f5efcfa85.jpg

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[Ali Tait]

Could easily just be getter overspray.

[Firebottle]

That would be my conclusion from the colour also>

The brown marks from well used power valves is quite different, unlikely to get the same with the small signal valves though.
Unfortunately appearance is no real indication of use.

[Lawrence001]

Thanks guys let me look again tomorrow as the photo seems to have exaggerated the difference, it's a less extreme difference and a bit browner than it looks here.

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[User211]

That would be my conclusion from the colour also>

The brown marks from well used power valves is quite different, unlikely to get the same with the small signal valves though.
Unfortunately appearance is no real indication of use.Scarily brown marks can appear quite quickly. I have some 211s that were completely clean but gained some brown staining up top after only a few months use at maybe 15-20 hours a week.