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How do you know tubes are used?

post #1 of 7
8/29/11 at 9:11pm
Thread Starter 

Just curious... I've seen this darker splotch on some of the tubes that I've bought in the past few months. Here's a pic...

Used Tube?.jpg

 

Does this mean it's used?

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post #2 of 7
8/29/11 at 9:22pm

No its just a mark left from when a reactive metal is used to remove any traces of oxygen from the tube during the manufacturing. 

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post #3 of 7
8/29/11 at 9:25pm
Thread Starter 

Good to know. I'm seeing this on a few CBS 7730s I recently bought. Thought they were NOS.

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post #4 of 7
8/29/11 at 9:33pm

You really do need a tube tester to be totally sure they're still good.

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post #5 of 7
8/29/11 at 10:16pm
Thread Starter 

How much is that going to run me? I don't need the most badass tube tester. My local tube guy charges $2 a tube for testing. The guys gotta make money somehow.

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post #6 of 7
8/29/11 at 10:39pm

A nice B&K 606 might fit the bil.

Make sure it's been calibrated.

It's important to check the tester can test the tubes you intend to use in the future.

 

The marks are cathode boil off marks.

They can happen during manufacture or after heavy use.

 

To me it's important to check the tube for shorts and leaks and then for emissions etc.

 

Bob Putnak has a nice article, worth reading:

http://tubesound.com/2008/09/30/brown-or-black-getter-flashing-does-not-mean-used/

 

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post #7 of 7
8/29/11 at 11:50pm

Yes tube testers are good, you'll also know if the tube is bad if it goes white. It looks cool, but it means all the gas was lost in the tube.

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