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Tube question. Blue ring on tube

Discussion in 'Amps and Cabs [BG]' started by goran, Aug 31, 2003.


  1. goran

    goran

    Dec 17, 2002
    Croatia
    Endorsing Artist: Bartolini
    One of 6L6 tubes in my Fender Bassman 100 is glowing with a blue light (like a ring somewhere about middle of tube). When you look amp from behind, it is 1st tube. I noticed that tube No 4 is starting to glow blue too but less intense. It happens with standby on and off. Sound is more or less the same.

    Is this normal? Should I take amp to technician?
     
  2. FretNoMore

    FretNoMore * Cooking with GAS *

    Jan 25, 2002
    The frozen north
    Disclaimer: I'm in no way an expert! :)

    I searched the www for "tube blue glow" and found several sites that all say a faint blue glow is normal and nothing to worry about as long as the amp works normally.

    Here is one of the sites.

    Maybe a bonafide tube-head will step in and verify this.
     
  3. goran

    goran

    Dec 17, 2002
    Croatia
    Endorsing Artist: Bartolini
    I did that too...

    Tubes didn't glow blue until today.
     
  4. If it happens with the amp on standby, I'm puzzled. Grid windings will glow blue when subjected to enough voltage and it will cast a haze outward from the plate vents, but it shouldn't be happening on standby. It would be normal for this to happen with most 6L6GC's in a Bassman 100. It could also mean that the tube is leaking mildly and the air getting inside is becoming ionized from the cathode and glowing.

    Are the edges of the getter (the silvery coating inside the glass) turning milky white or light brown? That would be sure sign of a tube leaking air. Some leakage is normal and occurs under normal prolonged use because the glass begins to gap around the pins where the heat has caused it to expand and contract. You need only worry if the glass itself starts looking frosted; that's a dead or dying tube from leakage.
     
  5. goran

    goran

    Dec 17, 2002
    Croatia
    Endorsing Artist: Bartolini
     
  6. Ok, now that makes more sense. If they glowed BEFORE the amp was switched to "run," something could be screwy. You just didn't give the grid voltage enough time to bleed off. I think your amp and the tubes are probably fine. If you notice anything else weird, let us know.
     
  7. goran

    goran

    Dec 17, 2002
    Croatia
    Endorsing Artist: Bartolini
    Amp is OK. I checked tubes last night and noticed that they stop glowing blue when i put standby off.

    Phew!! I was worried about it having to be repaired. (this things usually happen when you're broke)

    Thanks, Psycho