tube question...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by parntz145, Sep 25, 2005.


  1. parntz145

    parntz145 Member

    Messages:
    100
    Joined:
    Sep 24, 2004
    Location:
    NJ
    I purchased a quad of SED EL34. They maybe at the most have 10 hours of playtime on them. Today I noticed that the 2 center tubes are glowing a dark blueish color. 1 tube at the top and the other down near the base. It looks almost like someone is holding a lighter to the tube and you see the reflection of the blue flame. I dont notice any tone loss at all. They sound fine. I also noticed that when I turn the standby switch on the blue glow goes away, but as soon as I turn the switch off the blue come back. Is this normal or do I have a problem with these tubes?
     
  2. Roccaforte Amps

    Roccaforte Amps Member

    Messages:
    6,120
    Joined:
    May 23, 2002






    Its gass inside the tube, its conductive and will light up like neon.
    Some try to say its the lead or crystal in the glass that causes this, but its not. Its gas, I won't use tubes that glow blue,
    because its conductive it can cause the tube to "open up" and draw current when its not supposed to.
     
  3. Reeek

    Reeek Member

    Messages:
    1,208
    Joined:
    Feb 1, 2005
    Location:
    Reno, NV
    I glad to hear your perspective on the blue glow, Doug because you'll often hear that it "doesn't hurt" as well. At least there is another perspective to consider ;)
     
  4. Blue Strat

    Blue Strat Member

    Messages:
    29,978
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    Not necessarliy true. More often than not, there's absolutely no problem.

    From "Sylvania Engineering Data Service", vol. 1, pg 23 (1960?):

    BLUE GLOWS

    Blue Glows are not tube detriments per se. They are, however, suspects in the eyes of many receiving tube users for lack of a full understanding of their origins. There are several types of Blue Glow which can be described as follows:

    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 affect upon receiver performance, and in fact, tubes displaying this phenomenon are particularily good with respect to gas content.

    MERCURY VAPOR HAZE-is a blue-violet glow associated with those tube types which rely upon mercury vapor for proper operation. In such cases, the blue glow should be evident indicating proper operation.

    GAS-produces a blue haze, generally confined to the vicinity of the mount structure. The proper function of gas types such as thyratrons, voltage regulator and voltage reference tubes, requires the presence of this glow as an indication of proper tube operation. Some voltage regulators use neon instead of argon and as a result exhibit a pink-orange glow. It is, however, a distinct detriment in vacuum receiving types, where the presence of gas in large amounts can cause malfunction of the equipment.
     
  5. Roccaforte Amps

    Roccaforte Amps Member

    Messages:
    6,120
    Joined:
    May 23, 2002






    Well, I've seen blue glowing tubes run away many times,
    use what you will.
     

Share This Page