[R-390] Gettering old tubes

[Bernie Doran]

I be gettering most of mi toobs offa that ebay thing.Bernie
----- Original Message ----- 
From: "Robert Moses" <rhmoses at earthlink.net>
To: <R-390 at mailman.qth.net>
Sent: Saturday, March 05, 2011 8:25 PM
Subject: Re: [R-390] Gettering old tubes


>I have this gut feeling that this is not something that you would likely
> do more than once! <wink> The high current surges that would be produced
> would tend to melt the screens / grids of the tubes unless the tube had
> a metal envelope. If the envelope was glass then the spot of getter on
> the inside of the tube would tend to get very hot and create thermal
> stresses in the glass envelope that could cause cracking.
>
> Lloyd Godsey wrote:
>
>>Ever tried putting one in a microwave? (GRINNNNNN)
>>Thanx
>>Lloyd Godsey  KK7IZ
>>kk7iz at cox.net
>>480-620-7145
>>www.kk7iz-parts.com
>>www.lloydsdipsydumpster.com/
>>
>>--------------------------------------------------
>>From: "2002tii" <bmw2002tii at nerdshack.com>
>>Sent: Wednesday, March 02, 2011 12:40 PM
>>To: <R-390 at mailman.qth.net>
>>Subject: Re: [R-390] Gettering old tubes
>>
>>
>>
>>>Tisha wrote:
>>>
>>>
>>>
>>>>But I recall seeing in some of those
>>>>1960's vintage tube videos (someone posted a link to them a year or so
>>>>ago)
>>>>that they would getter a tube after manufacturing by heating it via an
>>>>induction furnace.
>>>>
>>>>There really is not that much to an induction heating device. Maybe
>>>>someone
>>>>wants to try to make one and see if they can make the getter to 
>>>>reactivate
>>>>on old tubes. There is a limited amount of barium/ zirconium/ sodium 
>>>>(name
>>>>your own metallic gettering materials here). As long as the metal has 
>>>>not
>>>>entirely turned into an oxide it still has some gettering potential and
>>>>may
>>>>be able to scavenge some gas molecules out of the tube.
>>>>
>>>>
>>>Induction heating is how they fire the getter in the first place, not
>>>how one would rejuvinate a tube.  Once all of the volatile metals
>>>have boiled off the getter and deposited on the envelope -- and this
>>>is done to completion during manufacture -- there is no point to
>>>re-firing the getter.  (The getters in some large transmitting tubes
>>>are not fired to completion at the time of manufacture, but this does
>>>not affect the discussion of receiving tubes.)
>>>
>>>Gettering is most effective while the vaporized metal is in transit
>>>from the getter to the envelope -- when it is very hot and very
>>>reactive.  The residual "gettering" that happens during a tube's life
>>>is very, very slow because the flashing is in the much less reactive
>>>solid state and the tube envelope would melt before the flashing
>>>reached a temperature at which it would be really effective.
>>>
>>>To de-gas a tube post-manufacture, you need to heat the getter
>>>flashing (the deposit on the tube envelope) to the point that it
>>>reacts with any residual gas molecules in the tube.  This means that
>>>you need to get the envelope to operating temperature (or preferably,
>>>well beyond) and keep it there long enough for all of the gas
>>>molecules to react.  Since (i) the gas density is very low, and (ii)
>>>each molecule needs to hit the flashing many times before it reacts,
>>>the time required for the getter flash to clear the gas from
>>>decades-old tubes (assuming that there is enough flashing present to
>>>do so) is measured in months or years, not minutes.
>>>
>>>Thus, "residual gettering" can keep a tube relatively gas-free if it
>>>is in regular operation and the gas ingress is slow, but it is not a
>>>very promising way to react decades of gas ingress from a tube that
>>>has not been operating.  If you want to try, put the tubes into an
>>>oven (you want to heat the envelope evenly so as not to produce
>>>thermal stress), heat them just short of the point where the glass
>>>collapses, and leave them there for a few months.
>>>
>>>Best regards,
>>>
>>>Don
>>>
>>>
>>>Copyright 2011.  Not for redistribution.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>______________________________________________________________
>>>R-390 mailing list
>>>Home: http://mailman.qth.net/mailman/listinfo/r-390
>>>Help: http://mailman.qth.net/mmfaq.htm
>>>Post: mailto:R-390 at mailman.qth.net
>>>
>>>This list hosted by: http://www.qsl.net
>>>Please help support this email list: http://www.qsl.net/donate.html
>>>
>>>
>>
>>
>>
>>
>>
>>>No virus found in this incoming message.
>>>Checked by AVG - www.avg.com
>>>Version: 9.0.872 / Virus Database: 271.1.1/3477 - Release Date: 03/02/11
>>>00:34:00
>>>
>>>
>>>
>>______________________________________________________________
>>R-390 mailing list
>>Home: http://mailman.qth.net/mailman/listinfo/r-390
>>Help: http://mailman.qth.net/mmfaq.htm
>>Post: mailto:R-390 at mailman.qth.net
>>
>>This list hosted by: http://www.qsl.net
>>Please help support this email list: http://www.qsl.net/donate.html
>>
>>
>>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html