i have a sylvania 6sn7 chrome top that has a grey like halo inside glass just at edge where chrome stops and clear glass begins.
i have seen this grey like appearence in tubes that crack or fail !
is this normal in a old failing tube ?
should i expect this tube to fail soon?
it is in a 300B integrated and so far it still works ok.
just wondering about this because i have been watching 6sn7's on auction site and saw a tube that had the same hazey ring near the top of the tube like mine !
thanks for response.
i have seen this grey like appearence in tubes that crack or fail !
is this normal in a old failing tube ?
should i expect this tube to fail soon?
it is in a 300B integrated and so far it still works ok.
just wondering about this because i have been watching 6sn7's on auction site and saw a tube that had the same hazey ring near the top of the tube like mine !
thanks for response.
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Sounds like the getter has starting to oxidize as oxygen is being introduced into the tube.
The "chrome" is actually magnesium. It'll turn white as it oxidizes to magnesium oxide when oxygen (air) gets into the tube.
As long as there's getter material left, I suspect the tube will probably work OK, but it's likely reaching the end of its service life.
~Tom
The "chrome" is actually magnesium. It'll turn white as it oxidizes to magnesium oxide when oxygen (air) gets into the tube.
As long as there's getter material left, I suspect the tube will probably work OK, but it's likely reaching the end of its service life.
~Tom
safe to assume....
thanks for the explanation... it then seems safe to assume that any tube with that white -grey haze creep is then bad news-oxidation occuring in the tube vacuum ?
.... thanks
paul
thanks for the explanation... it then seems safe to assume that any tube with that white -grey haze creep is then bad news-oxidation occuring in the tube vacuum ?
.... thanks
paul
Obviously, if the the tube has a good vacuum, there wouldn't be any oxygen in the glass envelope. The fact that the getter has started to oxidize indicates that oxygen has gotten in, i.e. a seal is leaking. If this has happened suddenly, I'd consider the tube dead. If it took 50 years to get to a thin white line of oxidized getter, you can probably get a bit more life out of the tube. But unless we're talking some rare version of the 6SN7, you should be able to find a new replacement for not that much money. AES has plenty. Starting as low as $6. At those prices, I'd just replace it. The Sovtek tubes are pretty good IMO, though, I haven't tried their 6SN7.
~Tom
I have a number of very old Sylvania 6SN7 with that very slight whitish fringing on the edge of the getter - none have failed due to this issue in the 20 or so years I have been buying and using these tubes. (None tested gassy either) I've had one or two fail for other reasons - usually mechanical.
Back in the day, they probably didn't have the vacuum pumps we have today. Getting a good vacuum is surprisingly hard. The getter has reacted with what little oxygen was left after the bottle was sealed. Unless the white band of oxidized getter gets bigger, the tube is probably OK.
~Tom
Maybe yes; maybe no. I've seen the same thing myself with a 5U4GB -- that hazy halo surrounding the getter. This could be due to a slow leak, or it's a sign that the getter was flashed too soon during pump-down. As for the 5U4GB, it still tests strong, and has not failed in the five years it's been in service.
I also had a defective 807 that lit up like a thyratron, and yet showed no haze around the getter. If the 6SN7 is still working, chances are that there's no problem here.
In this case, it's a "Realistic Lifetime" that Rat Shack used to sell. Realistic never made their own VTs. They were a rebrander that bought factory seconds that had cosmetic flaws, and attached bases, stamped their logo on them and sold 'em.
I also had a couple of 6BQ6GTBs that were of the same brand that looked weird due to overheating that caused the glass to soften and begin to implode. These proved to be slightly gassy, as the bias would not settle down. Though there was no visible glow, they did test out as being gassy. So they don't last a lifetime after all.
Perfect Quad 1954 Sylvania Chrome Top 6SN7GTA Amp Tubes Black Triangular Plate | eBay
here is a link to pic of what i am seeing in my tubes.
here is a link to pic of what i am seeing in my tubes.
Those 6SN7 look very similar to a number of the older ones in my stash, I suspect they have been that way since the day they were produced. I've not ever had a problem with them either other than as previously remarked, and the ones I checked with the getter in this state were not gassy either.
hazey-foggy tube
on my tube (not pictured) the tube had previously not shown any such hazzieness as seen in those ebay tubes.... but a few weeks ago while causually using my equipment i noticed the appearance of it.
anyway just a note of futher interest.
not a expert but if buying a new tube i would shy away from one that looked like these. but maybe in the 50's things where different. nevertheless there are used 6sn7's that dont have this apperance.
thanks for reply.
paul
on my tube (not pictured) the tube had previously not shown any such hazzieness as seen in those ebay tubes.... but a few weeks ago while causually using my equipment i noticed the appearance of it.
anyway just a note of futher interest.
not a expert but if buying a new tube i would shy away from one that looked like these. but maybe in the 50's things where different. nevertheless there are used 6sn7's that dont have this apperance.
thanks for reply.
paul
If that's the case then this particular tube may well have a problem, and I should mention that my comments apply only to the Sylvanias - I've not really seen any other brand (IIRC) that had getters that appeared this way.
I also have much later Sylvanias that generally do not have the fringe of white/grayish gettering.
I also have much later Sylvanias that generally do not have the fringe of white/grayish gettering.
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