Flashing blue tubes

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by RMstrat, Mar 24, 2008.

  1. RMstrat

    RMstrat Member

    Messages:
    85
    Joined:
    Feb 28, 2008
    Any reason why my tubes would be flashing blue? I Play through a bassman reissue. I had a tube screamer and a digitron pedal hooked up. I turned bright channel, Normal channel, and master volume(amp has master volume mod) all the way up..Turned guitar all the way up and nailed it(very loud). amp starting going " woof,woof,woof,woof" starting and stopping just as you were saying that. I looked in the back and the tubes were flashing BLUE. They still had the orange color also. What Happened...it still plays fine...Ill try to get video.
     
  2. EarlTX

    EarlTX Member

    Messages:
    50
    Joined:
    Mar 12, 2008
    Typically, a output tube that's doing the BLUE deal is just a bunch of stray electrons hitting the glass envelope, and making it light up...no problem with that.

    The other deal sound (to me) like the power supply si 'bouncing'.
     
  3. burner

    burner Member

    Messages:
    2,614
    Joined:
    Dec 27, 2007
    Location:
    USA
    The blue flashing is normal.
    Unless of course it's some kind of non-typical "blue flashing"

    Hope this helped
    Love,
    burner.
     
  4. Greenbacker

    Greenbacker Member

    Messages:
    180
    Joined:
    Jan 16, 2007
    "Fluorescence: this type of glow is usually violet in color and most noticeable around the inside surface of the glass bulb. It is most pronounced on power tubes and is the product of electron bombardment of the glass taking place within the tube. It generally has no adverse effect upon receiver performance, and in fact, tubes displaying this phenomenon are particularly good with respect to gas content."
    REFERENCE: http://barney.webace.com.au/~electron/tubes/blueglo.htm, January 10th, 2005.

    Note: My Svetlana 6L6GCs glow blue too and they sound fantastic.
     
  5. stratman_el84

    stratman_el84 Member

    Messages:
    403
    Joined:
    Mar 16, 2008
    Location:
    Kalamazoo MI area.
    Yes, the blue glow on the bottles is a normal thing, more visible as more current flows through the tube(s).

    The strange sound could be, as stated, the power supply "bouncing", however I'd check for a microphonic power or preamp tube. Microphonic tubes are a bane of combo amps, and can cause some really strange effects.

    Cheers!

    Strat
     
  6. EarlTX

    EarlTX Member

    Messages:
    50
    Joined:
    Mar 12, 2008
    It's also possible that the output tube grids are suffering from blocking distortion when running at full tilt.
     
  7. stratman_el84

    stratman_el84 Member

    Messages:
    403
    Joined:
    Mar 16, 2008
    Location:
    Kalamazoo MI area.
    Yes, I suppose that's possible. I've worked on a number of the Bassman RI's with a fairly wide variety of tubes installed and have never encountered that phenomenon. Doesn't mean that's not what's happening. It could be that a borderline power tube might cause that to happen.

    I still think a microphonic or unstable/borderline preamp tube is much more likely, especially given the preamp was being hammered with a lot of extra signal from the pedals. That could cause an unstable/borderline or microphonic preamp tube to motorboat and go back and forth in to and out of cutoff.

    Cheers!

    Strat
     
  8. EarlTX

    EarlTX Member

    Messages:
    50
    Joined:
    Mar 12, 2008
    Stratman - It certainly is the easiest 1st step...change the tubes.. :)
     

Share This Page