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Old 8th March 2008, 01:06 AM   #1
nhuwar is offline nhuwar  United States
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Default Mercury vapor rectifier tube question

Ok I got 2 nos sylvania 872a's which as far as I can tell have never been fired up. Well I put a transformer on the filament to heat them up to make sure all is well and something weird happend.

When the plate got hot it had this scale that came off of it on the inside. It looks like burned paper honestly but it half way fell off the anode and it laying on the filament.

Has anyone ever incountered this phenomenon and will it effect the tubes functionality?

Thanks,


Nick
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Old 8th March 2008, 01:39 AM   #2
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Do NOT put high voltage on that tube! This is a very common occurrence with old mercury rectifier tubes like the 872 and 866A as well. I've seen this many times and it is a function of old age where the coating flakes off and gets between the elements. If you try and use it, it will arc and cause damage. Dispose of it safely and properly. I word to the wise should be sufficient.

edit: Actually, you were lucky that you heated it up and saw that. I could tell stories about what has happened when they arced over.

Victor
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Old 8th March 2008, 01:40 AM   #3
nhuwar is offline nhuwar  United States
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Well I have gotten the flake out of the diode structure and down in the bottom of the tube.

Is it still a bad tube?


And if it is I can't debarnacle the tube?


Nick
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Old 8th March 2008, 01:46 AM   #4
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I would not use it, nor would I sell it. There is no guarantee it will stay on the bottom. If you choose to use it, you do so at your own risk. You've been warned by the voice of experience.

Victor
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Old 8th March 2008, 02:05 AM   #5
nhuwar is offline nhuwar  United States
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Don't worry I wouldn't sell it Victor. If it arcs at all I will get rid of it. But only if I can get the scale out of the business area so to say.

But you know debarnacle was a very common pratices for curing problens in tubes. But I do relise this could introduce gas into the tube.


I figured a few short pulses at 10kv but extremely low current should do the trick. It's not like the tube could gernade from a half second pulse of high voltage at a few microamps.

Nick
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Old 9th March 2008, 04:34 PM   #6
nhuwar is offline nhuwar  United States
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Does anyone have any idea what type of metal the anode in these tubes are. I can't see the being tantalum because these wouldn't happen.


Any idea's??????????



Nick
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Old 9th March 2008, 06:07 PM   #7
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Just another semi wise word.
Don't apply high voltage to it without a dummy load.
Mercury rectifiers WILL flash over inside if o/c.
And, please shield your eyes from it, most generate a high degree of nasty ultra violet light that looks nice, but will damage your eyes.
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Old 9th March 2008, 06:48 PM   #8
Gluca is offline Gluca  Italy
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Quote:
Originally posted by itsmejto

And, please shield your eyes from it, most generate a high degree of nasty ultra violet light that looks nice, but will damage your eyes.
OH! I do love to stare at my 866A. Girls too. That's one very reason I use them. I will be blind for the UVs in my eyes and deaf for too many decibels in my ears, will I?

Gianluca
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Old 9th March 2008, 06:51 PM   #9
Trout is offline Trout  United States
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Is there actually any valid reason to even use such a tube anymore?

I am no rocket scientist, but I can not think of any especially with the risks invloved.
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Old 9th March 2008, 07:29 PM   #10
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Quote:
Originally posted by itsmejto

And, please shield your eyes from it, most generate a high degree of nasty ultra violet light that looks nice, but will damage your eyes.
Actually the short wave UV (the most dangerous kind) is stopped by the glass. Most of what you see is visible light with perhaps a little long wave UV

The only advantage to using mercury vapor rectifiers is a lower voltage drop with higher current capacity, plus a little noise from the gas.

Victor
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