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Tubes with a Blue Glow

Discussion in 'Amps and Cabs [BG]' started by chaosMK, Sep 23, 2005.


  1. chaosMK

    chaosMK

    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    I noticed that I was getting some fuzz distortion with my Mesa Bass 400 during rehearsal. I turned it around and could see two of the power tubes with a blueish glow on the inside. When I hit a note, the blue light would flare up a little more.

    I am wondering if this happened because a while back these discolored power tubes had gotten a little loose and I pushed them back in with my fingers.

    I guess it is time to call JJ's and do that 6550 upgrade. :rolleyes:
     
  2. Matt H

    Matt H

    Jul 30, 2005
    Ithaca, NY
    what kind of tubes are you running?

    6L6's tend to have a blue glow, and that's fairly standard for them...

    however, in other tubes, blue glow is usually a sign that they're starting to fail...
     
  3. Keeaumoku

    Keeaumoku

    Dec 29, 2004
    I think brother Matt is on to something here... While it's been many "blue" moons... pun intended :oops: ... since I had an all-tuber with 6L6s inside, I seem to remember they did, indeed, have a cool looking blue glow to them... HOWEVER, I don't recall ever seeing them "flare up" when striking notes??? I do recall being told that "flaring blues" (could be a song title/theme, or a name for a Blues Band... hmmmm) meant trouble with the old tuber amps. I used to love (still do...) looking at 'da tubes whenever I practiced.

    I have a VBA400... 'dat be made by Sir Jim Marshall for the uninformed (...and if he hasn't been knighted by Her Majesty, then I just did!)... and this brute is stocked with eight (8) 6550s... earth moving power here... and those towers of power tend to glow a lovely red-orange... and no "flare-ups!"

    So, I would have to say that brother Matt's question remains on the table: what 'kine tubes you get, li'dat, brah??? :cool:

    And... how old is your Mesa beast, anyway? Is it time for the proverbial oil change?
     
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The blue glow is normal, it's caused by the passage of electons. When you play harder more electrons flow.
    The orange color is in the filament heater in the tube. Different phenomena, also present in all tubes.
     
  5. protoz

    protoz

    Nov 30, 2000
    Iowa
    A buddy of mines 5150's tubes glow blue in some spots but they don't really flare at all.
     
  6. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Sounds like normal happy tubes. If they start glowing angry orange, then start worrying.

    If you're not happy with the tone your tubes are providing, then get a new set and try them out...keep the old ones on hand.

    My 400+ had tubes that were fine, and I switched them out for JJ's and the amp sounds much better.
     
  7. chaosMK

    chaosMK

    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    This is a 1982 Bass 400 with original 1982 6L6 tubes, and supposedly very little use with the previous owner. I've probably put about 60+ hours on it since purchase. The tubes say "Mesa Boogie" on them, so that must mean they are cheap chinese tubes.

    I have the channel 1 volume at around 7, the Master volume around 7-8, with nothing too extreme on the EQs, and get dirtyness in my sound when I hit low notes. I unplugged from my board and plugged in directly and the problem persisted.

    If I turn up the volume more, I get more of this fuzz/overdrive. Maybe this is regular tube overdrive? I thought overdriven tubes were supposed to sound really cool (and this doesnt), but I've never been a fan of distortion on bass.

    I have the head in a rack case (a normal one, not the super high roller bling case) on top of a folded towel to reduce vibrations. Run into a Powerhouse 4x10 cab.

    Only two of the tubes have a blue atmosphere on the inside, the rest are clear looking. This blueness and overdrive are new development. The problem is unwanted overdrive :scowl:
     
  8. protoz

    protoz

    Nov 30, 2000
    Iowa
    What kind of cab are you running? This is starting to sound more like you are hitting the breakup point or your cab is starting to fart out.
     
  9. chaosMK

    chaosMK

    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    Mesa Powerhouse 4x10
     
  10. AGCurry

    AGCurry

    Jun 29, 2005
    Kansas City
    The power tubes' blue glow is normal, and fluctuation of the blueness with output is normal too. If some of the power tubes are NOT glowing blue, I'd suspect that it's those tubes that may be failed or failing.

    I've never seen preamp tubes glow blue.
     
  11. chaosMK

    chaosMK

    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    I did some more reasearch and read somewhere that it isnt too uncommon to get the blue glow on certain tubes. It has something to do with gasses trapped inside the tube. Some opinions are that it isnt bad if it is static/not moving, if it dances around then you are SOL.

    Maybe the fuzz is just OD.
     
  12. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Yeah, generally speaking, the glow is either that that vacuum in the tube was not all the way there when it was made, or it has outgassed a bit. There is normally a blotch of a silvery material inside the bubble somewhere - known as a "getter" the purpose of which is to absorb these emissions before they become a problem. If these tubes never glowed before, they may be getting near end of life, but as others have said, they still work and sound good, don't worry. At the other extreme, if they get extremely gassy, they can arc over internally . . . . which, while fun to watch, does not sound like much . . .

    - Tim
     
  13. If they're from 1982, they're most likely NOT Chinese, but probably Sylvania/Philips 6L6GC's. The blue glow could be a lot things from bias issues to grid alignment of the tubes to the tubes gassing and dying. If you're getting a new unwanted distortion, it's time to get the amp serviced.
     
  14. chaosMK

    chaosMK

    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    Are those high quality tubes?
     
  15. Matt H

    Matt H

    Jul 30, 2005
    Ithaca, NY
    are those quality tubes? yes!!!

    However- if the amp has the original tubes from 1982, and barely has "any use on it"... that scares the pants out of me.

    Why?

    It probably needs a cap job. Electrolytics should get replaced every 15 years or so (this is NOT an exact figure, don't take it as such). As of right now, you've got a 23 year old amp that is "running on the original tubes". Why does this matter? Generally, if someone's running the original tubes, it means the amp hasn't been serviced. not always, but as a seriously cynical buyer, that's how i'd take it.

    i really don't know the exact setup of the amp, but a cap job at a respectable tech generally runs as high as 300 bucks.

    i'm not saying the unwanted distortion you're hearing is DEFINTELY from this, but it's far more likely than being related to the bluish glow IF the tube has the original caps in it.

    electrolytic caps are used for most values over 1uF in your average amp. The two places you'll find them in fixed-bias instrument amplifiers tend to be as 1) cathode bypass capacitors on preamp stages and 2) big big big high voltage ones in the power supply.

    The preamp cathode bypass caps are cheap (generally under a buck a piece). However, the ones in the power supply get pricy... bass amps tend to use high capacitance ones and run high voltages (for headroom and power out). Each cap could cost up to 15 bucks, and you might need like 8 of them.

    Then there's labor.
     
  16. Techmonkey

    Techmonkey

    Sep 4, 2004
    Wales, UK
    Sorry to be a tad off topic, but I was once helping out at a friend's gig where they were supporting Acey Slade's (Mr. Bone from the Murderdolls) new band. Man that gig kicked ass, but anyways, when we were setting up, before the venue opened, and they had the lighting rigs off, you could see a greenish glow coming from the vacuum tubes in their guitar amps!
     
  17. protoz

    protoz

    Nov 30, 2000
    Iowa
    I have a '68 Sunn with original tubes and I have no problems. It has been serviced within the past 5 years because the one whom did the servicing wrote on the metal casing and it was either 2000 or 2002 so I know it's at least been looked at before I got it.

    Unless the tubes actually go bad there is NO reason to change them at all.