Tubes over or under biased

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by lpstudio, Mar 13, 2008.

  1. lpstudio

    lpstudio Member

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    I have a 100 watt 1975 traynor that seems to have lost some clean headroom and when I dig into the strings I notice the tubes change to a blue kind of spark inside the tube. All power tubes do this at the same time. I just had the amp in to Gar gillies of Garnet amplifiers before he died R.I.P. and he checked the bias. Is the change of color power tube saturation or a bias problem or the fact my tubes are about 6 years old?
     
  2. slider313

    slider313 Silver Supporting Member

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    I would go with your tubes are 6 years old. The blue gas is normal in some power tubes. When retubing be sure to rebias.
     
  3. Trout

    Trout Member

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    Hey, a blue neon type glow or halo is a fairly normal phenomenon, But an arc=spark is not. If you are actually seeing an arc inside the power tube, I would most certainly stop running it and get it checked out. Since all 4 tubes are doing it, I suspect it is just the normal blue/purple neon type glow. Generally the glow dances with varying frequencies and notes. Many of my GE 6V6GTA's put on a great show when drop tuning and using a wah.
     
  4. lpstudio

    lpstudio Member

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    That is a perfect way to describe that wow I guess I won't worry about it but the tubes are just sovteks so I think I will change them anyway
     
  5. pgissi

    pgissi Member

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    The Blue Glow is an inert gas added to the tube. It used to distibuish american from euro made tubes with the european environmental restrictions preventing the use of the gas.

    Depending on how much and how hard you have played in these last 6 years, you may not need tubes, maybe the bias and/or plate voltage has drifted, the amp is 33years old!
     
  6. Blue Strat

    Blue Strat Member

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  7. donnyjaguar

    donnyjaguar Member

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    Those Europeans are a gas. :)
     
  8. pgissi

    pgissi Member

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    1st of all, I was reffering to NOS tubes and did not mean to suggest gas was added soley for the purpose of identifying the tube, that was purley incidental, its purpose was to improve evacuation during manufacture.

    One indication of it being an NOS american manuf tube was this from that same linked article-



    Since tubes are no longer manufactured in any countries with strong environmental laws (Us and Europe), the gas is used and being that all tubes comes from former Eastern Bloc Countires, China/SE Asia etc., the gas is still used.

    The original post asked about the "blue kind of spark", I am assuming he meant the blue glow.




    Per Terry Killgore ala Vintage Guitar Mag, NOS British, German manufac'ed tubes etc. do not have the gas and is one way to establish you have say some older Brimar or Mullard etc
     
  9. Blue Strat

    Blue Strat Member

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    Where's the "confused" smilie when you need it?
     
  10. mike80

    mike80 Member

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    Power tubes are not any of those tubes mentioned.



    There are no laws against argon, or neon. Argon is used in welding to displace oxygen, and is released into free-air. Neon signs are produced everyday.
     
  11. pgissi

    pgissi Member

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    No problemo,

    It was an informative article and he also talked about NOS tubes and why they are superior. It was as if the heavens opened up and now I just need to hit powerball.

    After I read his article I became a believer in NOS simply based on opinions of actual players etc. (his observations confirmed what players have been saying) but I have yet to take the plunge but its on my "bucket list"

    There must be something to it and since I did not start playing until '79 I may have had some brushes with tubes of this type playing my bro's 67 super, maybe my 79 Silverface Twin or a few other older fender and marshalls that rambled in with people we jammed with.

    I do believe I have an old pair of 6L6's somewhere that a friend took out of his BF twin and left in my dads garage which is a home for wayward tools and holds many jam memories etc.

    I will find them soon and realized I needed to do this after reading Terry article.

    No power tubes are not mentioned but you have to remember that only for guitar or hifi audio amplification are they called power tubes. As far as industry, they served a different purpose and were not called "power tubes".

    Find Terrys artticle and read it, its an aha moment
     

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