Sound of new production tubes

[Gene Pink]

A theory:

The cathode coatings mentioned both above and in links, all contain elements that have at least one radioactive isotope. Some emit alpha during decay, some emit beta, and their beta decay daughters tend to emit alpha, and so on down the decay chain. Lots of alpha coming off the coating, relatively speaking, as these are trace amounts.

An alpha particle is simply a helium nucleus without any electrons, and it will find electrons as soon as it hits anything that is willing to share electrons, and it then becomes helium, a gas.

Gas in a tube. A gassy tube.

I have no idea if the minuscule amount of helium being constantly produced would have an impact on tube performance, but maybe after 50 years...?

I dunno, this is just a theory.

Gene

 

[PRR]

All tubes have getters, the shiny stuff inside. This is really how the vacuum happens (the pump just gets the bulb empty-enough that the getter won't fill-up instantly).

I don't know, but assume, that He getters-up about as well as all the other stray gasses.

And a gassy tube shows symptoms. Tiny gas is excess grid current and abnormal bias.

 

[Gene Pink]

All tubes have getters, the shiny stuff inside. This is really how the vacuum happens (the pump just gets the bulb empty-enough that the getter won't fill-up instantly).

I don't know, but assume, that He getters-up about as well as all the other stray gasses.

I don't know either, but always assumed that the getter gets, by chemical reaction. Something reactive like oxygen being first on the list. Nitrogen, not far behind. Any metals with a vapor pressure above zero that can possibly react with the getter may be next.

But helium, being a noble gas with it's aristocratic nose-up-in-the-air properties, wants nothing to do with chemistry, as it is above all that nonsense of mingling with the other peasant elements in any covalent bonding, and feels that it is above marrying one.

And a gassy tube shows symptoms. Tiny gas is excess grid current and abnormal bias.

Hmmm, that might make for a good test. Ground the plate and wrap a few turns of wire around the outside of the tube. Energize the wire with really high voltage and high frequency, from a tesla coil in a dark room. Look for spectral lines, see what glows, indicating any gas that may be in there.

Gene

 

[PRR]

> helium, being a noble gas

One of the great classical getter papers is Getter Materials for Electron Tubes, Electronics magazine, October 1950, page 80. Extensive bibliography.
http://www.americanradiohistory.com/Archive-Electronics/50s/Electronics-1950-10.pdf  (34MB PDF!)
(page 84 of PDF)

I do not see Helium mentioned. Noble gases mentioned under Tantalum, which is expensive and needs to run hot to getter, so is not a major player in small tubes.

"Tantalum
"Certain metals are capable of incorporating gases, even noble gases, by solution in their bulk volume. The classical example is tantalum...."

 

[Gene Pink]

> helium, being a noble gas

One of the great classical getter papers is Getter Materials for Electron Tubes, Electronics magazine, October 1950, page 80. Extensive bibliography.
http://www.americanradiohistory.com/Archive-Electronics/50s/Electronics-1950-10.pdf  (34MB PDF!)
(page 84 of PDF)

That was a good read, thanks.

But it still leaves the question: Does helium buildup from alpha decay of cathode coatings, amount to enough to degrade tube function over several decades?

"Is there a nuclear physicist in the house?"

Gene

 

[Triode-Joe]

That was a good read, thanks.

But it still leaves the question: Does helium buildup from alpha decay of cathode coatings, amount to enough to degrade tube function over several decades?

"Is there a nuclear physicist in the house?"

Gene

I'm not a nuclear physicist, but I am a chemist and a mass spectroscopist for 30 some odd years. A quick look through some isotope reference books shows:

Barium has 1 natural radioactive isotope - 130Ba,  0.11% amount, double electron capture decay converts to Xenon, half-life > 1020 years

Strontium has 1 natural radioactive isotope - 90Sr,  trace amount, beta decay converts to 90Yttrium, half-life 28.9 years

Calcium has 2 natural isotopes -  48Ca,  0.187% amount, double electron capture converts to 48Titanium, half-life > 1019 years
                                                                      - 41Ca,  trace amount, electron capture converts to 41Potassium, half-life 1 x 105 years

No alpha decay and I don't see any He here from the radioactive isotopes of these getter materials. Noble gasses make up such a small amount of the air that was removed when the tube was pumped down, sealed and flashed that it's hard to believe He is any issue in NOS tube (or current manufacture for that case).

Joe

 

[gyraf]

Thanks, Joe..!

Jakob E.

 

[Gene Pink]

I'm not a nuclear physicist, but I am a chemist and a mass spectroscopist for 30 some odd years. A quick look through some isotope reference books shows:

Barium has 1 natural radioactive isotope - 130Ba,  0.11% amount, double electron capture decay converts to Xenon, half-life > 1020 years

Strontium has 1 natural radioactive isotope - 90Sr,  trace amount, beta decay converts to 90Yttrium, half-life 28.9 years

Calcium has 2 natural isotopes -  48Ca,  0.187% amount, double electron capture converts to 48Titanium, half-life > 1019 years
                                                                      - 41Ca,  trace amount, electron capture converts to 41Potassium, half-life 1 x 105 years

No alpha decay and I don't see any He here from the radioactive isotopes of these getter materials. Noble gasses make up such a small amount of the air that was removed when the tube was pumped down, sealed and flashed that it's hard to believe He is any issue in NOS tube (or current manufacture for that case).

Joe

Nice reply, and I thank you for it.

You didn't mention the thorium 228 decay chain, a trace amount, but then again, how much is a trace?

Several alpha decays, with short half lifes, the longest being 1.9 years, ending in lead 208, although this would be a 2 year problem, not a 50 year problem, if it actually were a problem.

A cool decay chain chart is attached.

Gene

 

[Triode-Joe]

Nice reply, and I thank you for it.

You didn't mention the thorium 228 decay chain, a trace amount, but then again, how much is a trace?

Several alpha decays, with short half lifes, the longest being 1.9 years, ending in lead 208, although this would be a 2 year problem, not a 50 year problem, if it actually were a problem.

A cool decay chain chart is attached.

Gene

If we limit the scope of this subject to (small) receiving tubes, then the barium, strontium and calcium would be in the form of oxides on a nickel / nickel alloy tube used as an indirectly heated cathode. The wire inside the tube would be tungsten or some alloy and heated to a dull red. There would be no need for thoriated-tungsten here as there is no emission from the heating wire. The tube getter, again in a receiving tube, is going to be some form of barium (eg. barium azide) and flashed while the tube is under vacuum but before it's sealed. There will be a small amount of outgassing from the various metals and mica in the tube, but this doesn't happen until the tube gets hot during use and will happen to some extent with ALL tubes.

In my experience "trace" means less than 10ppm of one compound in another, but there is no official definition I know of so it can mean something quite different to engineers.

Your multi-step (complex) thorium decay chart is correct, you have to love the actinides,  but I question if there is enough thorium to decay to make enough helium to cause an effect here.

Traditionally higher quality tubes meant: better quality chemical oxides, better quality metals and mica, cleaning and passivating and drying the internal parts, premium quality glass and as hard of a vacuum as possible. All these things did and do cost more money and time for a higher quality tube. With the exception of the Western Electrics, Bell Labs, Telefunken Uhm facilities, Bendix, etc. that made tubes to a performance specification  with little (or no) regard for cost of manufacture, all tubes have had and will have to have certain compromises of cost / quality to keep them affordable. This may be more of the reason for your new tube / NOS tube quality questions than helium.  Just my opinion. 

Joe

 

[PRR]

> In my experience "trace" means less than 10ppm of one compound in another, but there is no official definition I know of so it can mean something quite different to engineers.

Different contexts:

Early "vacuum tubes" had SotA vacuum, but gas effects dominated until vacuum technology improved several orders of magnitude.

Early semiconductors were wonky until material purity was improved. IIRC the dopants which make Silicon one type or the other are at around level of 10^-14, which is beyond parts per billion (instead of ppm).

 

[CJ]

Mullard Factory

https://www.youtube.com/watch?v=GDvF89Bh27Y

 

[ruffrecords]

Ian,

Where would you buy new-production Russian tubes today, if you wanted to be relatively sure of their heritage?

I may as well try some of them out, the NOS JAN-types are getting horribly expensive lately...

Jakob E.

Just remembered that the 6933EH and 12AX7WA that I use can both be obtained from tube town in Germany

https://www.tube-town.net

Cheers

Ian

 

[My3gger]

Local reseller has TAD "premium matched" tubes with 6 months waranty at the same price as TAD directly.
They are honest about their origin, although one tube of 6L6 pair from China failed in combo amp after maybe 20 hours of not loud playing, it had warranty... Preamp tubes i bought were Svetlana and Ei Nis, those work well. I find it pretty time consuming asking about origin when there are a few different manufacturers of the same type, website doesn't tell that for those with warranty.

Since then i found another local reseller who has EH, JJ, Sovtek, Tungsol and other new production, some NOS are left too. If asked he tests and makes pairs of new production preamp tubes, this seems to be rare and prices are still good. He feels that NOS stocks became too expensive and hard to find in quantity for good testing at normal prices, so when his Ei Nis stock is depleted they are switching to new production.
For sure there are local shops in other countries wher they build gear and test new production tubes (circuits at hand, more experiences, etc.). I will report how it goes with both untested and tested.