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Old 19th July 2012, 01:42 AM   #1
pbkrag is offline pbkrag  United States
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Default Tube Going Bad?

Is the tube on the right bad? (the getter fading) I only recently finished my SSE. The tube only has couple of weeks on it. I didn't notice it at first, but I didn't really look that close either, so I'm not sure if getting worse. You can only see the difference when it's warmed up, and it doesn't sound bad. If so, how long til it fails? What happens when it does?
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Old 25th July 2012, 02:23 AM   #2
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It looks like the tube on the right came out of the factory and the vacuum wasn't hard. If the getter is finished eating the leftover air molecules, the tube may still have a very long life ahead. I'd keep a close eye (and ear) on it for anything funny.

Worst case scenario is an ever-so-slight vacuum leak, which is causing the premature getter wear. Likely result of this kind of failure is a catastrophic light show complete with sparks. Don't worry, you'll know when it happens.
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Old 25th July 2012, 04:27 PM   #3
rknize is offline rknize  United States
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That's a tired-looking getter. Not a good sign. If possible, I would try to get it replaced under warranty (if your source offers one).
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Old 25th July 2012, 04:48 PM   #4
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I had a Tung Sol reissue EL34 do that, I stopped using them...
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Old 25th July 2012, 05:43 PM   #5
pbkrag is offline pbkrag  United States
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The tube is an JJ EL34 I checked with the vendor and its still under warranty so they are willing to replace it. Although I'm considering hanging onto it with the chance of catching a good a fireworks show.

Thanks All,
Pete
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Old 26th July 2012, 06:52 PM   #6
rknize is offline rknize  United States
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Could be a good show. Just be aware that there exists the possibility that your cathode resistor and/or bypass cap could be taken out in the process.
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Old 27th July 2012, 12:36 AM   #7
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Just be aware that there exists the possibility that your cathode resistor and/or bypass cap could be taken out in the process.
Been there, blown that. I bought a sealed military bulk pack of 100 NOS Sylvania 6V6GTB's at an auction. Upon opening the carton it was obvious that about 25 of the tubes had gone to air, the getters were completely white. A few more looked like yours, OK but not as shiney as all the rest. I tossed the obvious bad tubes and put the box on the shelf here in an air conditioned room. Over a period of about 10 years several more have turned white and a few more don't look so good.

A few years back I decided to test all the remaining tubes in an SSE and label the distortion number on each tube. A vintage, well used brown base Sylvania was used for comparison. I think I saved less than 40 of the tubes and some of those have since failed just sitting on the shelf. A few more died during use, but a few have held up well. This shows that even Sylvania can make a bad batch. I got a bad batch of Sylvania 35LR6's too.

I decided to "test" some of the tubes that worked but had high distortion. The tube shown here had some silver getter left, but was thin and whitish at the edges. It didn't take long for me to use that up. Did I exceed the specs????? Do tubes glow???? YES, RED, WHITE AND BLUE all at the same time.

YES, the tube died, but it was already useless....but the cathode bypass cap decided to blow its guts all over everything. See the droplets of condensed steam/electrolyte goo all over. It is most evident on the scope probe, which hasn't been the same since. Careful examination of the cap just to the right of the dead 6V6 reveals a slight brownish gap in the vent. Yes all of that mess came out of that little crack.

In the real world, if the tube is leaking air, its distortion will go up first, but maybe not enough to notice right away. A perfect tube should not show a blue glow inside the plate amongst the grids. Blue flourescense on the glass is OK. Air or "gas" will cause the glow inside the plate. This glow will increase as the tube gets worse. The glow can cause the tube current to increase, eventually leading to a runaway red plate cap exploding condition.
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