blue glow in vacuum tube

Discussion in 'The Workbench' started by scat7s, Jan 20, 2011.

  1. scat7s

    scat7s New Member VIP Member

    Joined:
    Nov 19, 2010
    Messages:
    13,874
    Likes Received:
    7,292
    peeked in the back of my amp yesterday and noticed one of my rca 6v6's had a smallish spot of blue glow to it.

    is this something i should be concerned about? i know ive read about this b4, but cant remember what the verdict was...it still sounds fantastic, but i did notice a faint pop now and then, nothing obnoxious, pretty subtle really. but a faint pop nontheless.

    could these things be related?
     
  2. diesect20022000

    diesect20022000 Well-Known Member VIP Member

    Joined:
    Sep 5, 2010
    Messages:
    19,576
    Likes Received:
    7,167
    Location:
    44076
    no. large amounts will indicate ionization and slow tube death but, small amounts are normal.
     
  3. Alabama Thunderpussy

    Alabama Thunderpussy Well-Known Member

    Joined:
    Oct 23, 2010
    Messages:
    2,051
    Likes Received:
    1,045
    Location:
    Northern CA
    Not at all. Blue glow is a common effect. If anything it can indicate a hotter bias. As I've understood it, it's a phenomenon that occurs when electrons and ions strike each other at high velocity inside the vacuum tube.

    The glass envelope of the tube is actually very mildly conductive at high temperatures (inside the vacuum), hence the blue glow tends to gravitate towards certain areas of the bottle, as you'll notice. Sometime's it's just a spot, other times it's more of a fractal design.

    Obviously, if you decrease the negative bias voltage (bringing it closer to 0, hence LESS negative) and more current is passing, more electrons are moving within the bottle and at a faster rate, hence more blue glow.
     
    Last edited: Jan 21, 2011
  4. MartyStrat54

    MartyStrat54 Well-Known Member

    Joined:
    Feb 21, 2009
    Messages:
    25,999
    Likes Received:
    9,455
    Location:
    Licksville
    When tubes are made, they pull a vacuum on the tube. The better the vacuum, the better quality the tube. Once the vacuum is pulled a device inside the tube called a getter is activated. The getter splatters a barium laced stain on the tube (generally on the top). This leaves a shiny, mirror-like stain on the tube. The purpose of the getter is to further eliminate any extraneous air left in the tube. The effects of the getter last throughout the life of the tube. Even though all of these precautions are used, all the air cannot be completely removed. The small amount of gas in the tube will cause the light blue glow you see. It is harmless.

    In current production tubes, there is a chance for more air (gas) to be inside the tube. Therefore the blue glow is even greater.
     
  5. scat7s

    scat7s New Member VIP Member

    Joined:
    Nov 19, 2010
    Messages:
    13,874
    Likes Received:
    7,292
    great, thanks guys.
     
  6. RiverRatt

    RiverRatt Well-Known Member VIP Member

    Joined:
    May 2, 2008
    Messages:
    8,452
    Likes Received:
    2,593
    Location:
    Between Memphis and Nashville
    Be very worried if the gas in the tube is glowing violet. That's a tube that's getting air in somewhere. Beam power tubes seem to be more prone to the blue glow. I think I have some pics of each.

    Here's a dying 5Y3:

    [​IMG]

    This is a pair of 5881s with the blue glow:

    [​IMG]
     
  7. big dooley

    big dooley Well-Known Member VIP Member

    Joined:
    Sep 2, 2008
    Messages:
    7,338
    Likes Received:
    2,847
    Location:
    zeeland
    INcrease the negative voltage on pin 5 and you DEcrease the amount of electrons flowing to the anode... that's how it works
    yes i like screwing ants :D
     
  8. Rahlstin

    Rahlstin Well-Known Member

    Joined:
    Jan 10, 2011
    Messages:
    1,067
    Likes Received:
    503
    Location:
    Lethbridge, Alberta
    I think the blue glow is cool. A budy of mine had a Mesa amp back in the late 80's that looked like a purple and blue plasma storm in the back of the amp. He used that thing for years and years that way with no troubles.
     
  9. Alabama Thunderpussy

    Alabama Thunderpussy Well-Known Member

    Joined:
    Oct 23, 2010
    Messages:
    2,051
    Likes Received:
    1,045
    Location:
    Northern CA

    YES!! Thank you for catching that. I meant voltage increase as in closer to positive. I should have said DEcrease. :fingersx:

    Fixed.

    Now, tell the fine folks here WHY increasing the negative voltage on pin 5 results in a decrease of electrons flowing to the anode. ;-)
     
  10. MM54

    MM54 New Member

    Joined:
    Feb 14, 2010
    Messages:
    4,113
    Likes Received:
    590
    Location:
    Erie, PA
    It's more negative so it repels more electrons back towards the cathode (as like charges repel), preventing them from hitting the plate, or passing the plate and whacking their tiny little negative heads off the glass :p
     
  11. scat7s

    scat7s New Member VIP Member

    Joined:
    Nov 19, 2010
    Messages:
    13,874
    Likes Received:
    7,292

    funny...
     
  12. MM54

    MM54 New Member

    Joined:
    Feb 14, 2010
    Messages:
    4,113
    Likes Received:
    590
    Location:
    Erie, PA
    Hey, you'd be blue too if you smacked your head off a piece of glass a few billion times thicker than you while traveling at the speed of light ;)
     
  13. MajorNut1967

    MajorNut1967 New Member

    Joined:
    Jul 30, 2009
    Messages:
    3,883
    Likes Received:
    334
    well great the baboons are loose!
     
  14. MartyStrat54

    MartyStrat54 Well-Known Member

    Joined:
    Feb 21, 2009
    Messages:
    25,999
    Likes Received:
    9,455
    Location:
    Licksville
    How about a misplaced circus chimp?
     
  15. FourT6and2

    FourT6and2 Active Member

    Joined:
    Dec 3, 2010
    Messages:
    169
    Likes Received:
    54
    As others have said, blue glow is just an indication that there isn't a 100% vacuum inside the tube. That's normal. If the tubes glow blue while the amp is in standby, then you have a problem.
     
  16. Wilder Amplification

    Wilder Amplification New Member

    Joined:
    Oct 12, 2009
    Messages:
    6,163
    Likes Received:
    700
    Location:
    Fresno, CA
    IMO the blue glow in a valve is one of the most badass things about them. Looks kinda eerie on some of them.
     
  17. demonufo

    demonufo New Member

    Joined:
    Oct 23, 2010
    Messages:
    2,211
    Likes Received:
    254
    Location:
    defunctprofilesville
    Mercury Arc Rectifiers;
    [ame=http://www.youtube.com/watch?v=lNAKL9qtnIA]YouTube - Hewittic Mercury-arc Rectifier of Manx Electric Railway[/ame]
    Now THAT'S badass blue glow.
     
  18. scat7s

    scat7s New Member VIP Member

    Joined:
    Nov 19, 2010
    Messages:
    13,874
    Likes Received:
    7,292
    it is very cool looking, beautiful color.
     
  19. topcat 70

    topcat 70 New Member

    Joined:
    Nov 3, 2010
    Messages:
    311
    Likes Received:
    32
    Location:
    Norfolk. U.K
  20. demonufo

    demonufo New Member

    Joined:
    Oct 23, 2010
    Messages:
    2,211
    Likes Received:
    254
    Location:
    defunctprofilesville
    :lol:
    Duck and cover...
     

Share This Page