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output valve not receiving power

Discussion in 'Amps and Cabs [BG]' started by turdferguson, Mar 23, 2017.

  1. turdferguson


    Nov 11, 2014

    i have a mesa/boogie bass 400+ which blew a couple of fuses the other night at a rather inopportune time. last night i had some time to fiddle around a bit and i have determined that one of the power/output tube valves is not working properly.

    all twelve output tubes were recently replaced by a professional, and i have verified that all twelve tubes are still AT LEAST good enough to light up, so i'm ASSUMING there is something wrong with the valve. it's the very first tube if you start counting from front to back, left to right (facing the rear of the amplifier) that will not light up, regardless of which tube i place in the valve. it powers up and passes a signal, sounds great, but it's going through fuses at a record pace. (yes they are the right fuses)

    does anyone know what might cause this? are there multiple possible reasons? i have tried searching online and i haven't managed to find anything that addresses this specific problem. at this point, i'm leaning towards selling the amp, though i absolutely love the tone. if i can pinpoint the problem and save the time and trouble of getting a pro diagnostic done before selling the head, that would be great.
  2. AstroSonic

    AstroSonic Supporting Member

    Dec 10, 2009
    rural New Mexico
    Just to clarify: are you saying that none of the output tubes will work in 'the very first tube (socket) if you start counting from front to back, left to right'? Or that all the tubes work, but the amp blows fuses pretty quickly? Or, one of the tubes (the glass things) does not work in any of the sockets? Not trying to give you a hard time... just trying to understand the problem.
  3. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Fuses blowing is a symptom of a deeper problem and it sounds like something that will require a qualified tech to fix.
    BassmanPaul, AstroSonic and wcriley like this.
  4. Nighttrain1127

    Nighttrain1127 Supporting Member

    Nov 27, 2004
    Near Worcester MA
    That was my first reaction if it is blowing Fuses stop putting in new fuses you will only cause more damage.
    Munjibunga likes this.
  5. turdferguson


    Nov 11, 2014
    thanks everyone. i'm pretty sure i knew it wasnt going to be anything simple. the thing that really grinds my gears is that it was blowing fuses a while back and i took it to a FRIEND's shop and he told me all i needed was new power tubes. so we replaced the output tubes, and it worked beautifully for months.
  6. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Could be another blown power tube. Tubes are like that...most will work great for years, and one could blow on you tomorrow, even if it's new. At any rate, I know nothing about Mesa tube amps other than that. And it's always best to get some pro help unless you can narrow down the broken tube yourself.
    TinIndian and Bim1959 like this.
  7. BassmanPaul

    BassmanPaul Inactive

    When you say the tubes “light up” do you mean that the heaters are working, orange glow in the centre of the tube, or do you mean the blue glow that signifies the tubes are conducting?
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Contact customer service, generally we would recommend a factory authorized service shop to handle repairs as they will have the necessary experience and documentation to service this properly.

    "Friends" generally aren't equipped to service these things properly with the needed attention to detail.
    TinIndian likes this.
  9. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    If your putting other good tubes in the socket and they don't light up. Then its not getting heater voltage. So its need to be fixed. But if other heaters are working and one socket doesn't then connections have broke lose and other sockets need to be looked at and touched up. So it don't happen again. Common stuff needs a little extra care and look over so gigging won't find basic stuff that preventive maintenance would have fixed
  10. turdferguson


    Nov 11, 2014
    my friend will remain nameless but he runs a legitimate shop and he is trusted in the local industry which is
    orange glow
  11. turdferguson


    Nov 11, 2014
  12. turdferguson


    Nov 11, 2014
    he's a friend but he is also a reputable, legitimate repair tech with enough experience that he opened his own shop a few years ago and has done quite well for himself. i emphasized the word friend b/c when i put the original post up i was very frustrated and i still feel like maybe he overlooked a serious issue and just assumed that fresh output tubes would solve my problem last year. i will definitely look into getting a factory authorized tech to go through it. thanks
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I mentioned this because the factory techs do see quite a few amps from techs in the field that just don't have the experience with the product and don't know the revision history or what specifically to look for. It's better (and a lot cheaper) if they don't have to undo incorrect previous repair attempts.

    The glow from the heater may mean nothing at all, or it may be part of the problem (unlikely).
  14. turdferguson


    Nov 11, 2014
    thanks again for taking the time to reply. i didn't mean to disparage my friend. his shop is actually listed as one of the authorized service centers in my area on the mesa site. -name and address withheld
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Cool, then follow up with him and suggest that he contact service center tech. support.
    BassmanPaul likes this.
  16. turdferguson


    Nov 11, 2014
    thanks again
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