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#1
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Tube flashing inspection = new/old
You test a tube on your tester and it's 100%+ and you drop the filament
voltage one step wait half a minute and with little needle deflection if any - a good sign of lots of life left BUT I've just been told that inspection of the flashing can really give you a better idea of the tubes usage - So I have several same make / year 12AX7 that are supposed to be nos and of the group there is one that has about 65% the amount of flashing inside the top as the others do - Is this a sign of many hours usage or production variations? |
#2
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Ozzy 2005 said:
You test a tube on your tester and it's 100%+ and you drop the filament voltage one step wait half a minute and with little needle deflection if any - a good sign of lots of life left BUT I've just been told that inspection of the flashing can really give you a better idea of the tubes usage - So I have several same make / year 12AX7 that are supposed to be nos and of the group there is one that has about 65% the amount of flashing inside the top as the others do - Is this a sign of many hours usage or production variations? None of the above. It's just that the heaters in certain tubes are covered with some kind of coating. Some brands have the coating extended all the way to the ends of the heater, others do not. What you see is the heater lighting up due to the lower resistance when cold, and where the coating isn't applied. Any tube with this heater construction will show this "flashing", whether old and worn out or brand new out of the box. Nothing to worry about, actually. Philips and associated brands (Mullard, Valvo, Mazda etc.) in particular are well known for their "flashing" . Telefunkens as a rule do not show this effect. -- Sander de Waal " SOA of a KT88? Sufficient. " |
#3
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You test a tube on your tester and it's 100%+ and you drop the filament
voltage one step wait half a minute and with little needle deflection if any - a good sign of lots of life left BUT I've just been told that inspection of the flashing can really give you a better idea of the tubes usage - So I have several same make / year 12AX7 that are supposed to be nos and of the group there is one that has about 65% the amount of flashing inside the top as the others do - Is this a sign of many hours usage or production variations? None of the above. It's just that the heaters in certain tubes are covered with some kind of coating. Some brands have the coating extended all the way to the ends of the heater, others do not. What you see is the heater lighting up due to the lower resistance when cold, and where the coating isn't applied. Any tube with this heater construction will show this "flashing", whether old and worn out or brand new out of the box. Nothing to worry about, actually. Philips and associated brands (Mullard, Valvo, Mazda etc.) in particular are well known for their "flashing" . Telefunkens as a rule do not show this effect. -- Sander de Waal Sander has confused the "flash" of light when powering up a tube (common on Mullard tubes) with the size of the silver getter "flashing" (the silver colored area created when the tube is new), which is what the original poster was asking about. The size of the silver colored getter FLASHING is an indicator of how much internal gas has been absorbed since the tube was made. This can be an indicator of use and wear of the tube, or it can be an indicator of slight vacuum leakage in the glass envelope. In either case, I could not consider a tube to be NOS, if it has lost a significant amount of it's original flashing. In the case of most 12AX7, this silver area normally extended down to first mica when the tube was manufactured. cheers! cowboy |
#4
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"cowboy" cacheoverflow@yahooDOTcom said:
Sander has confused the "flash" of light when powering up a tube (common on Mullard tubes) with the size of the silver getter "flashing" (the silver colored area created when the tube is new), which is what the original poster was asking about. OOOPS!!!! Thanks Cowboy, you're right of course. -- Sander de Waal " SOA of a KT88? Sufficient. " |
#5
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Sander deWaal wrote:
"cowboy" cacheoverflow@yahooDOTcom said: Sander has confused the "flash" of light when powering up a tube (common on Mullard tubes) with the size of the silver getter "flashing" (the silver colored area created when the tube is new), which is what the original poster was asking about. OOOPS!!!! Thanks Cowboy, you're right of course. Thanks guys ! I can't stand these people say NOS unused and now I know they are full of it by the photos of these tubes with almost no getter flashing left. Saved me lots of trouble. |
#6
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On Mon, 14 Mar 2005 12:39:02 +0000, Ozzy 2005 wrote:
BUT I've just been told that inspection of the flashing can really give you a better idea of the tubes usage - Like, who? Is there some problem with telling us who said that? Frankly, I'd like to help, but I'd like to know who the mysterious fount of this BS is, so I can go attack it at its source. I'm not into shadow-boxing. -- Ned Carlson Triode Electronics Chicago,IL USA www.triodeelectronics.com |
#7
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On Mon, 14 Mar 2005 12:39:02 +0000, Ozzy 2005 wrote: BUT I've just been told that inspection of the flashing can really give you a better idea of the tubes usage - Like, who? Is there some problem with telling us who said that? Frankly, I'd like to help, but I'd like to know who the mysterious fount of this BS is, so I can go attack it at its source. I'm not into shadow-boxing. -- Ned Carlson Triode Electronics Chicago,IL USA www.triodeelectronics.com I think saying the tube's "current condition" would be more accurate than saying "usage". The flashing on a tube can degrade for a lot of reasons, and not all of them involve any usage. I have unpacked 50 year old NOS tubes that were in sealed boxes (the kind you have to rip open to get the tube out) and the flashing was degraded. Some tubes are notoriously "leaky". A good example is the GE made VT-4C broadcast triode. These should have a huge flashing that is 4 inches in diameter at least, and I have seen NOS ones rot on the shelf, such that the flashing was about as big as a quarter. Needless to say, these gassy tubes burn up in the first 5 minutes that 1250V is applied to the plate. So what I am saying is, a reduced flashing does not necessarily indicate any malice on the part of the seller, but it DOES indicate a tube that is no longer going to function as new. I would further say that the flashing is the most reliable visual indicator of a tube's current condition, but it should still be tested for shorts & transconductance, as well as being tested in a real world application, such as an amplifier. for folks who want to learn more about extending tube life and assessing the condition of a tube, I can highly recommend Bob Tomer's classic 1960 bible on the subject, now out of print, information can be found he http://www.amazon.com/exec/obidos/tg...l/-/188258029X cheers! cowboy cacheoverflow AT yahoo DOT com (and I am a big fan of Uncle Ned's expertise, something I cannot say about most "experts" in the tube audio world) |
#8
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Thanks guys ! I can't stand these people say NOS unused and now I know they are full of it by the photos of these tubes with almost no getter flashing left. Saved me lots of trouble. There was likely wide variation of the amount of getter material applied to the getter ring or D holder, and how much get flashed onto the inside of the glass envelope. But if you see some white then there's been some gas in there. All white means that the vacuum all leaked out.... Other than that I don't think you can really tell how used a tube is by looking at the getter. |
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