Getter used up but tube is fine.

Discussion in 'Tube Audio' started by maxhifi, Dec 29, 2017.

  1. maxhifi

    maxhifi AK Subscriber Subscriber

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    Check this out:

    I often see people asking about judging the condition of a tube by the condition of its getter... Here's a Sylvania 5933 which has seen years of use in my RCA power amplifier. The getter is almost gone, but yet the tubes bias properly, test good, and sound great. I have some spare time during the holidays, so decided to do some work on the RCA amps. I was thinking to install some NOS USSR G-807s I keep as spares for these amplifiers, but those 5933s just aren't done yet. Anyway this is definitely the case of worst looking getters in good tubesI've come across.
    DSC_0333-768x1361.JPG
     

     

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  2. sKiZo

    sKiZo Hates received: 8642 Subscriber

    The getter is more for cleanup of mfg defects and one final pass at max vacuum than anything else, so it's not all that critical for daily use once the tube's been running for a while. You MAY end up having some residual flaking of components gathering in the base of the tube, and that MAY eventually short the tube.

    (Wouldn't be surprised if half that build up isn't old getter.) <G>

    PS - I've had folk tell me my KT120's are on their way out because of the gray halo on the getter flash, but hey, they've been like that since I got em ...

    [​IMG]
     
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  3. a_retent

    a_retent Daddy's little shadow Subscriber

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    That is soooo good to know, really! My kt120s look exactly like the ones in your pic and I was told the same thing. More importantly, I was dreading a re-tube right know because that would mean the purchase of (16) kt120s and (8) 6N1Ps.
     
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  4. sKiZo

    sKiZo Hates received: 8642 Subscriber

    Happy to be of service - Mine are maybe a couple thousand hours anyway and going strong ...
     
  5. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    I've got a quad of various branded 7591's with getters like that. They won't bias any higher than 15ma on a FISHER 800c or Sansui 1000A. Good enough to prove out the outputs before I put in the new tubes on a rebuilt unit, for now.
     
  6. maxhifi

    maxhifi AK Subscriber Subscriber

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    That's what surprised me about these, they bias perfectly fine, and make power too, but all that's left of the getter is a light brown haze which is completely transparent
     

     

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  7. arts

    arts Super Member

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    Somewhat correct,but not completely true.

    Accurate information is available in the manufacturing and chemistry texts (both are rare,but you may find them online) associated with vacuum tube manufacture.

    The getter remains fully active throughout the life of the tube,and is critical in maintaining both the tubes performance and longevity.The reason the getter begins fading is due to the liberation of gases from various elements during operation,which,in effect,deplete the getter. The effect is magnified and/or accelerated in tubes that have had poor processing during manufacture,internal sub components that were of inadequate purity or were incompletely out-gassed before assembly,or in the case of a top quality tube,being operated for extended periods at or beyond rated dissipitation limits,causing abnormal outgassing due to the elevated temperatures. Also,getters (in receiving-type tubes) require a certain level of heat to become and remain active during operation.Again,this is common scientific principle and knowledge.

    The gray halo on the getter flash seems to be quite common with the KT120.What is worrisome is the rapid depletion of the gettering in many of these tubes,despite their not having been abused.As I have already stated the possible reasons for getter depletion,you may draw or even research your own conclusions.

    Also,while I haven't heard of or seen directly any outright catastrophic failures involving the KT120,I have directly seen that the longevity of many of these tubes is less than what should be considered normal for such an ''overrated'' tube being used in place of a ''lesser'' (6550) tube.

    The only truly accurate indication of a power tubes performance is measuring the Imax or power output.And that doesn't fall into the realm of many tube-testers!
     
  8. Lavane

    Lavane AK Subscriber Subscriber

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    I have a Magnavox 9303 with the original mullard EL84's and one is brown at the top but it still sounds fine.
     
  9. maxhifi

    maxhifi AK Subscriber Subscriber

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    Old tubes really can last, the sylvania in the first post has outlasted at least five phono cartridges. I've heard 2000 hours quoted as normal power tube longevity, but I think that's extremely conservative.
     
  10. gadget73

    gadget73 junk junkie Subscriber

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    depends entirely on how its used or abused. What a tube lasts at design max operating conditions vs what it lasts at design center or less are very different things.
     
  11. arts

    arts Super Member

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    If anybody has any further interest in gettering,I would suggest investigating this link. The site itself is an absolute treasure-trove of technical reading material.

    http://www.tubebooks.org/technical_books_online.htm

    This is the book in question,and the relevant material begins on (book) page 519.This link will direct you to the books table of contents,you may then just return to the main site and download the entire text:

    http://www.tubebooks.org/Books/intro_RCA_1962_Electron_Tube_Design.pdf
     
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  12. CopperWizard

    CopperWizard Well-Known Member

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    "Old tubes never die, they just lose their "getter." I'm of no help here.
     
  13. Retrovert

    Retrovert AK Subscriber Subscriber

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    The getter color comes in two main varieties, with the difference arising from the two types of deposition during firing:
    Shiny: Slower vaporization oxidizes the initial barium so subsequent layer deposition occurs in a better vacuum with lower oxidation, but this tends to seal each layer against further incursion of residual gas.

    Dark or Dull
    : Rapid vaporization creates heterogenous layers which are porous, so residual gas may continue to diffuse into the layers.​

    The color is a manufacturing issue, not an operating issue. A white getter is fully oxidized and indicates the gas gods have smote thine tube for its sins.

    The getter cannot simply vanish from a sealed tube, so a vanishing getter must either (a) be re-deposited as a metallic composition elsewhere in the tube, including on the glass, or (b) chemically react with gas in the tube, flake off the glass, and fall into the bottom of the tube. The only source for gas is:
    (a) absorbed/adsorbed gas in the metallic structures (generally dealt with during pump-down) and slowly liberated over time (insignificant amounts)
    (b) water liberated by mica from overheating and then decomposed (can be significant)
    (c) atmospheric entering via a bad seal​

    So a missing getter indicates either (a) gross overheating or (b) a slow leak. In either case that tube is beginning its great and final journey to the landfill.
     
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  14. sanford12

    sanford12 Old Stuff New Stuff As long as it's Good Stuff Subscriber

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    Now I always thought the getter was the round, square, or D shaped ring and the silver looking coating was sacrificial flashing for tube impurities.
     
  15. Retrovert

    Retrovert AK Subscriber Subscriber

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    The shape you describe merely holds the getter, a metallic alloy or mixture, which is then heated to the boiling point in an induction furnace. As the metal boils it reacts with any residual gas to create metallic oxides which maintains the vacuum..

    The metallic color, bright or dull as I above described, on the interior of the envelope is the boiled off getter which has deposited on the glass. The metal wire which held the getter has no purpose once the getter has been flashed.
     
  16. mjw21a

    mjw21a Super Member

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    Yeah, my KT120's are the same too since day one

    ae_1508212832258.jpg
     

     

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  17. Retrovert

    Retrovert AK Subscriber Subscriber

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    Exactly. The getter's color, dull matte or gleaming sheen, again, is, a function of how rapidly the getter was flashed and the metal deposited. Unless the getter is being oxidized by gas in the tube—either created by excessive heat or entering through a bad seal—the color will not change over time from shiny to matte.

    People on the internet spout a whole lot of nonsense about vacuum tubes without understanding even the most basic physics, engineering, or science, and this nonsense is then endlessly repeated and recirculated until it becomes dogma about which people pontificate. I have seen discussions with heated arguements that one metallic color vs. another somehow indicates a different "sound", discussed in pompous and pretentious terms normally reserved for descriptions of wine, cheese, or halitosis.
     
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  18. maxhifi

    maxhifi AK Subscriber Subscriber

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    Haha halitosis. I hope that discussion stays far away :)

    I think anyone who has worked with tubes for a while can spot a tube which has seen extended service hours a mile away. Little silver dots appear above the heater, sometimes brown stains appear on the glass, and in power tubes, the getter starts to go away. What really surprised me with these Sylvania tubes, is that despite hours of use well past what's claimed as longevity, and despite the sorry state of the getter, they still function properly.
     
  19. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    Interesting observation on the KT120s.
    I bought a quad new for an amp . I used for 3-4 years.
    My best guess was about 1500 hours.
    When I sold amp with them , they looked brand new.
    I bought a used quad last year on BT. Which i since sold. Unknown time or conditions. The seemed to work fine but look more like what was described earlier.
    (My uneducated guess was, they were in the third quarter):idea: (maybe right after halftime)
    I wonder if there were quality issues early on?
     
  20. Retrovert

    Retrovert AK Subscriber Subscriber

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    As far as power tubes, the glass envelope softens and discolors with excessive temperature; that deformity may increase permeability which, in turn, leads to getter reaction. Excessive heat can also bake gas out of the mica and cathode by destroying the chemical structure.
     

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