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Old 19th May 2011, 02:33 PM   #1
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Default Physical Tube Diagnosis?

I am selling all these old vacuum tubes. Most are obviously unused, and have never been taken from their box.

Until I sell a few more items, I am without a way to test these tubes.

My wondering is to whether there is any way at all to look at a vacuum tube and know that it is shot.

I admit, I am new to this field and don't have much in the way of technical experience. Some of the tubes sound as if a filament or something is loose inside of the glass, I don't know if this means it is ruined or not. Others may has a milky appearance that can be wiped clean. Others seem to have a bit of moisture on the outside of the glass.

If there are any physically apparent characteristics that can be used to indicate life or death in the tube, I would be fascinated and very pleased to know!

Thanks,
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Old 19th May 2011, 02:56 PM   #2
SY is offline SY  United States
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If the getter has gone white, the tube is bad. otherwise, the only way to know good or bad is to test them electrically. There's lots of folklore out there about visual inspection, but don't believe any of it.
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Old 19th May 2011, 02:59 PM   #3
TheGimp is offline TheGimp  United States
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Indicators of used tubes include staining of the internal glass with grey/brown clear deposites in line with openings in the plate of the tube (not to be confused with getter flash). Some tubes are burned in at the factory and will exhibit this even when NOS.

In addition any transition of the getter flash (black or silver coating on part of the inside of the tube) to white indicates a tube is gassy and will be bad.

Beyond those two obvious issues, and the ability to measure the filament/heater to show it is not open, there is little one can do without a tube tester or testing the tube in an operating circuit.
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Old 19th May 2011, 03:02 PM   #4
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Quote:
Originally Posted by SY View Post
If the getter has gone white, the tube is bad. otherwise, the only way to know good or bad is to test them electrically. There's lots of folklore out there about visual inspection, but don't believe any of it.
So where the getter would be a chrome color, it will be white. Do you mean a solid bright white, or a dull white? Thanks for the tip, that's a big help. I don't think I have come across any that have turned to white yet.
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Old 19th May 2011, 03:05 PM   #5
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Quote:
Originally Posted by TheGimp View Post
Indicators of used tubes include staining of the internal glass with grey/brown clear deposites in line with openings in the plate of the tube (not to be confused with getter flash). Some tubes are burned in at the factory and will exhibit this even when NOS.

In addition any transition of the getter flash (black or silver coating on part of the inside of the tube) to white indicates a tube is gassy and will be bad.

Beyond those two obvious issues, and the ability to measure the filament/heater to show it is not open, there is little one can do without a tube tester or testing the tube in an operating circuit.
The grey you are talking about, will it be kind of matte?
I have an RCA 7C5 that is matte gray all over, with the top being the chrome color, I am guessing this is normal appearance for this kind of tube?
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Old 19th May 2011, 03:17 PM   #6
TheGimp is offline TheGimp  United States
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Flakey powdery white.

Look at this site. It has a good set of pictures and explaination.

http://www.jacmusic.com/articles/Getterology/index.htm

Last edited by TheGimp; 19th May 2011 at 03:19 PM.
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Old 19th May 2011, 03:43 PM   #7
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Flakey powdery white.

Look at this site. It has a good set of pictures and explaination.

Unbenanntes Dokument

I had just read that page before I got your message. There was some good information on there. Hopefully I won't have to lean on this lacking method for long, I am looking at some Testers on eBay right now. It's just such a pain to find one that fits the bill. I'm willing to spend up to 150 dollars on the right one.



Anyone here have a good tube tester for sale???
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