Something I'm curious about is whether or not a true New Old Stock (That is a tube that was never put into service) Heater Cathode can have emission staining .
I dont' believe filament (DHT) tubes will exhibit this phenomenon as much.
I occasionally see tubes advertised as NOS with what looks like a matching box, but there is the telltale gray ring aove the heater cathode on the inside of the top glass. Everything about the tube looks to be new, clear glass, no dust/dirt/grime, pristine lettering, etc.
Could otherwise identical tubes show one with staining, and one without if both were burned in at the factory?
In particular I'm talking about early two digit series tubes like 27, 37, 55, 56, 76, adn early number letter series like the 6G5, 6F5, etc.
I dont' believe filament (DHT) tubes will exhibit this phenomenon as much.
I occasionally see tubes advertised as NOS with what looks like a matching box, but there is the telltale gray ring aove the heater cathode on the inside of the top glass. Everything about the tube looks to be new, clear glass, no dust/dirt/grime, pristine lettering, etc.
Could otherwise identical tubes show one with staining, and one without if both were burned in at the factory?
In particular I'm talking about early two digit series tubes like 27, 37, 55, 56, 76, adn early number letter series like the 6G5, 6F5, etc.
In my world any internal shadows or discoloration on receiving tubes is an indication of use. This, of course, excludes the intentional smoke gray dag coating in some tube types.
I have dozens of NOS 27, 56, 76, 6P5, etc. and the glass is always clear just above the heater/cathode. It takes many hours of use to generate the silver/gray marks above the heater/cathode.
This is another case of "it depends". Sometimes, you find uneven deposition of getter material even in unused tubes, always the small signal types that didn't use a lot of getter material in the first place. It doesn't necessarily mean they're really used and someone is trying to deliberately put one over.
With large signal types, you sometimes see the migration of getter material, with a silvery spot over the cathode if they were installed vertically. It takes a lot of time and heat for that to build up, and if you see that, it's not NOS.
You also see cosmetic defects, including a gray "halo" around the silvery getter deposit. This happens when the getter is fired too soon during pump down. These types otherwise test as good, but were rejected at the factory. Repackagers, such as Realistic, would buy these seconds, stamp their own logos on them for resale. I have a "Realistic Lifetime" 5U4GB which is exactly like that. Other than the cosmetic defect, it still works. You'll sometimes see other types of cosmetic defects as well. These could still be legitimate NOS.
I have a sample of a 6LQ6 that shows multiple rings around the getter that's indicative of migration. This one was obviously in some hard service, probably as a TV HD final. TV manufacturers frequently ran the VTs on the edge of max ratings, and HD duty is pretty demanding service.
With large signal types, you sometimes see the migration of getter material, with a silvery spot over the cathode if they were installed vertically. It takes a lot of time and heat for that to build up, and if you see that, it's not NOS.
You also see cosmetic defects, including a gray "halo" around the silvery getter deposit. This happens when the getter is fired too soon during pump down. These types otherwise test as good, but were rejected at the factory. Repackagers, such as Realistic, would buy these seconds, stamp their own logos on them for resale. I have a "Realistic Lifetime" 5U4GB which is exactly like that. Other than the cosmetic defect, it still works. You'll sometimes see other types of cosmetic defects as well. These could still be legitimate NOS.
I have a sample of a 6LQ6 that shows multiple rings around the getter that's indicative of migration. This one was obviously in some hard service, probably as a TV HD final. TV manufacturers frequently ran the VTs on the edge of max ratings, and HD duty is pretty demanding service.
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