Tubes with shiny areas on the side?

[Khron]

I recently got my hands on a huge(-ish) job lot of mostly German tubes from some attic-find or whatever. As i was sorting through them, in order to take inventory of what's what, i noticed a minority of them (of various types) seem to have developed shiny spots or an entire shiny coating around the mid-height area of the tube. I doubt it's a sign of loss-of-vacuum, since the getters at the top of said tubes are still shiny themselves, but they still don't inspire all that much confidence.

Can any of you greybeards (and i mean that with the utmost respect experience-wise, anyway) shed light on this? I haven't dealt all that much with used / old tubes, so i'm not quite sure what to make of it myself.

 

[JohnRoberts]

search "getter material".

I am not the tube guy here but I do have gray hair, and a search engine. Getter - Wikipedia

JR

 

[Khron]

So, apart from the silver "hat", would there also be a coating inside the rest of the glass envelope? And/or would the amount of additional visible silver coverage on the inside point towards how long the tube has been in use?

 

[JohnRoberts]

I am just paraphrasing what I read at that wiki page... the getter material reacts with oxygen to remove it. The getter product vapor condenses on the cooler glass envelope.

Logically it suggests time in service, with a variable for original oxygen content, and probably more stuff I do not grok.

I am not the tube guy here.... I do recall seeing shiny tube glass on old tubes back when I messed with repairing old radios and TV sets as a kid.

JR

 

[rock soderstrom]

AI translated from a german source:

"The bulb is made of relatively thin-walled glass and is pumped empty of air, since the inner parts of the tube only work properly in an airless space. It is almost impossible to achieve the necessary degree of vacuum by pumping alone, so the last remnants of the still harmful gas are rendered harmless by a special measure: After pumping out, a small amount of e.g. barium, aluminium or magnesium alloy is evaporated inside the tube by inductive heating. The substance is deposited as a mirror on the glass wall and binds the last harmful gas residues still present in the tube. In addition, the mirror-like coating absorbs the tiny gas residues that can later be released from the inner parts of the tube during operation, thus achieving a permanent high vacuum. This internal mirror is also called a "getter". If the bulb is damaged, the tube draws air, which is externally noticeable by a discolouration of the getter mirror, the tube has become unusable."

As far as I know, this is the so-called getter mirror, or getter precipitation(?), which does not always have to be at the upper end of the tube.

A dark (almost black) deposit on the getter mirror indicates consumption, this is carbon that is deposited. When a lot of carbon was deposited, the tube was used more. If the getter turns white, the tube has drawn air and is KIA.

To answer your question, the tubes can be in good condition if they look like this. I have some that look like this and measure flawless.

Please correct me if I am wrong. It was explained to me like this a long time ago.

Edit: those EF80 are pretty good for a transformerless spring reverb driver.

 

[rock soderstrom]

Most of you will know this. A defective tube without vacuum. The tip of the tube is very sensitive, here the tube was de-pumped and then sealed during production. This area must not be subjected to strong mechanical stress, otherwise the glass will break easily.

 

[Khron]

To answer your question, the tubes can be in good condition if they look like this. I have some that look like this and measure flawless.

Thanks for the confirmation!

I've seen vacuum-less tubes - the EL34's in this Randall RG50TC i grabbed as faulty a bunch of years ago, had lost vacuum and the getter went white and apparently "crumbly".

 

[Tubetec]

You do find a build up of deposits on the glass on some tubes types ,
its mainly miniature high powered RF tubes you see it , from TV sets and radios ,

Its not an indicator of a good or bad tube but appearance tends to worsen with age .

 

[auddoc]

The silver chrome-like "coating" on the interior of the tube glass is normal, in my experience. Do I know what the origin of this is? No. As it shows up on brand-new tubes, one must assume that it is a byproduct of manufacture. However, when you see a large white area, that appears almost powdery, inside, I believe that means that vacuum is lost and the tube is gassy or "pooched". I just serviced a Marshall combo amp that ALL four EL-84/ 7881 output tubes had White hats inside the top section interior glass of each power tube. I have never seen all four tubes fail like this, in 50 or so years of doing this stuff. Tube replacement worked fine too, after the bias was set properly. Any ideas while all four would fail in the same manner?

 

[murrayatuptown]

Some old tubes/valves had black glass & other features that were 'special'. Extra mirror, if it's extra getter, I would think means extra getter 'reserve' and potentially a better tube.

Agree with comment on RF power tubes, like thoriated tungsten filament types 3-500,3-1000,4-1000, etc), and some halogen lamps, glass can darken in spots from many hours of use...I think it's material vapor redeposited from the cathode/filament. Greybeards or silverbacks didn't like that at 'hamfests'-they'd remark things like the tube was probably down to <80% emission & keep walking.

Murray

 

[Tubetec]

If all four power tubes suffered a loss of vaccum Id suspect physical shock was the cause ,
a drop from a height maybe ,check for cracks around thebase , if the bias voltage faded you might expect to see melted anodes or maybe a burnt output transformer primary . check the output transformer for integrity in any case before putting in new tubes .

 

[Disco Volante]

Could be a coating to shield the glass from stray electrons, to prevent gasrelease from the glass, like the EF91: The EF91. I've seen and used these kinds of "coated" tubes and see no reason to think they are less "good".
Congrats on your find;-)

 

[S.Samuelsson]

Hi.

Can any of you greybeards

It is SILVER, damnit .
Just like a working getter flash .

seem to have developed shiny spots or an entire shiny coating around the mid-height area of the tube.

AFAIK, that's not exactly getter flash even though it's origins are usually the same materials, but rather deposits from the mesh screen coating and stray getter material atoms on tubes like EF80 & EF41.
The stray electrons remove and carry them onto the glass.

That kind of a "getter hue" (not a native speaker here so there may be an official word for it) in places there's no getter rings or -cups can be an indication of how much the tube has been used, and especially when buying used tubes and obviously wanting to pay as little as possible, is used as such as can be expected.

However:
A hue like that -EDIT: or the lack of it- doesn't necessarily tell anything about the tube performancewise, unless one has deep knowledge about that particular tube from the same manufacturer and from the same production period.
The amount of certain materials did vary a lot over the years, and so does the deposits.
Economics and profit played obviously a huge part in tube manufacturing, and also new material compounds were developed and tested.

Testing or getting them tested is really the only way to tell how they perform.

Regards,
Sam

 

[Khron]

@S.Samuelsson

Thanks a lot for that detailed explanation! And due apologies for my improper addressing...

 

[KIDVOX]

AI translated from a german source:

"The bulb is made of relatively thin-walled glass and is pumped empty of air, since the inner parts of the tube only work properly in an airless space. It is almost impossible to achieve the necessary degree of vacuum by pumping alone, so the last remnants of the still harmful gas are rendered harmless by a special measure: After pumping out, a small amount of e.g. barium, aluminium or magnesium alloy is evaporated inside the tube by inductive heating. The substance is deposited as a mirror on the glass wall and binds the last harmful gas residues still present in the tube. In addition, the mirror-like coating absorbs the tiny gas residues that can later be released from the inner parts of the tube during operation, thus achieving a permanent high vacuum. This internal mirror is also called a "getter". If the bulb is damaged, the tube draws air, which is externally noticeable by a discolouration of the getter mirror, the tube has become unusable."

As far as I know, this is the so-called getter mirror, or getter precipitation(?), which does not always have to be at the upper end of the tube.

A dark (almost black) deposit on the getter mirror indicates consumption, this is carbon that is deposited. When a lot of carbon was deposited, the tube was used more. If the getter turns white, the tube has drawn air and is KIA.

To answer your question, the tubes can be in good condition if they look like this. I have some that look like this and measure flawless.

Please correct me if I am wrong. It was explained to me like this a long time ago.

Edit: those EF80 are pretty good for a transformerless spring reverb driver.

I did see a video of tubes being made once. The tubes are warmed up a little and a masive static charge is applied to the outside of the tube and any metalic vapour is deposited in one place where it will do no harm. Then in use as more of the tube is evaporated it also settles on the glass.

 

[amplexus]

I'm not an old guy but I AM a tube guy and those are normal, and in fact necessary. It's the 'getter' which is a flashing of a barium azide compound done after the tube envelope is evacuated with an RF induction heater (not 'static charge' as has been suggested). A small amount of the barium compound is put in the 'getter' ring or dish and when heated by induction it 'flashes off' and creates a barium coating on the tube. It's purpose is to absorb any stray gas molecules that may be left behind after the vacuum is pulled, or that may off-gas from the internal components once the tube is sealed and heat cycled in normal use..

Normal getter flashes will be anything from bright and shiny silver- almost mirror like- to black or brownish, there's a pretty wide variation on that spectrum. But they should be relatively even in appearance (tho some discolouration spots are fine), and they should have reasonably defined edges with a little bit of feathering. Older tubes may have a more feathered edge to them. They should always be completely opaque unless 'used up'.

While the getter appearance isn't always an indicator of tube condition, in general you should be suspect of a tube where the getter edges have faded significantly, and are very feathered, or getters that look even slightly translucent. This usually indicates a fair amount of use.

Any whiteness to the getter should be immediately suspect as that indicates partial or full loss of vacuum. A getter that has gone white and chalky always says vacuum loss and that tube is done. On exposure to air you get white barium oxide. (Don't lick it)

Behind the getter flash you should see either a circular, D shaped, or occasionally rectangular ring, or a small 'dish', supported off the tube structure in some way. Technically this is called the 'getter' and the deposit is called the 'flash' but the terms are more or less interchangeable in general use.

There are also, in used tubes- mostly power tubes- sometimes darkened 'smokey' marks on the glass, usually only found directly in line with holes in the tube plate structure. These are bits of the tube parts (cathode/screen/plate coatings) that have been carried there over time by electrons accelerated towards the plates that 'miss' and pass through the hole. These marks look more translucent, they are never shiny, and they often have the same general shape as the hole in the plate. This is always an indication of tube use and wear- so anyone who tries to pass off a tube with those marks as NOS should be told in which direction to ****. If in doubt, these marks will never have a getter ring or dish behind them- and if your getter flash has faded THAT much to be mistaken for these, then the tube is suspect anyway.

Getter flashes can be in any location on the tube. It became widespread practice to place them at the top of the tube, but it is not uncommon to see them at the bottom (sometimes almost invisible below the tube base on bigger bottles), or at the sides, or askew at an angle on the top, or even multiple flashes- especially in big glass enveloped tubes. There's no standard requirement for position, so It will usually be wherever the manufacturer feels it was convenient. Having a 'double getter' can sometimes be considered a mark of manufacturing quality, you may see it more often in JAN and other military spec'd or ruggedized tubes.

Rarer to see is black or grey glass tubes- this is not getter flashing, it's a sheilding coating meant to reduce noise. I don't know of any modern tube that does this (maybe one of the TAD or Shugang models now that i think on it), but it was common in older tubes. These will still have getters, they just won't be externally visible usually.

 

[Scott Harmonic]

we aren't all looking at the guy's pics ;-) the usual getter flash is visible (at the top of the tubes) That's not what OP is asking about. He shows a separate metallic band encircling the middle of the tube envelope.- i'm pretty sure that's what he's asking about, and I'm pretty sure it's not usual ;-)

 

[Khron]

we aren't all looking at the guy's pics ;-) the usual getter flash is visible (at the top of the tubes) That's not what OP is asking about. He shows a separate metallic band encircling the middle of the tube envelope.- i'm pretty sure that's what he's asking about, and I'm pretty sure it's not usual ;-)

To some extent that might be true, but i was skeptical about possibly seeming ungrateful for the information shared x) But there's been some pertinent stuff "exposed" as well

 

[S.Samuelsson]

Hi.

Thanks a lot for that detailed explanation!

You're welcome.

And due apologies for my improper addressing...

, no problem, we silverbeards are used to it.

He shows a separate metallic band encircling the middle of the tube envelope.- i'm pretty sure that's what he's asking about,

That's correct.

and I'm pretty sure it's not usual ;-)

IMLE (I'm more of a MI-amp than a radio or TV tube hobbyist) it's somewhat common with the tubes that have a mesh screen around the internal structure.
Not all such tubes exhibit the same behaviour though, probably due to the fact that the materials changed during the years or decades of production.
And because there was more than one manufacturer that used the said internal construction and not everyone used the same methods or materials.

Without material analysis it's also impossible to tell what the metal -or metal compound- is, pretty much every metal that was used in tube manufacturing (and many others as well) looks silvery when flashed onto a glass suface in a vacuum.
Except for the precious metals, it's usually the colour of the oxide layer we use to visually tell various metals apart.
In theory, something about the material could be found out by examining the way the flash oxidises when the envelope is broken, but that would obviously mean that the tube is then a goner.

So, IMO it's always better to test the tubes in order to find out if they're usable or not, but I do agree that the academic discussion about the "flash in the unusual/wrong place" is interesting.
Even though that the majority of the replies concentrate explaining the normal flash .
It could well be that the explanation I was told decades ago and accepted to be the correct one is actually somewhat incorrect, even though it does make perfect sense material- and constructionwise.

Regards,
Sam

 

[Mr. Moscode]

I learned something tonight. Thank you. I knew what getters are but I didn't know how they were made. Genius, those Tube Gods!!