Mesa Bass 400+ volume issue

Discussion in 'Amps and Cabs [BG]' started by nukes_da_bass, Apr 29, 2012.

  1. nukes_da_bass

    nukes_da_bass Inactive

    Feb 19, 2006
    west suburban boston
    ...So the last two gigs I had intermittent volume issues with the 400+.

    Wed night at an Ivy League formal dance I didn't lose volume til the first encore. Something about my band (The Hep-Tet) makes it impossible to get to my amp during performance ( and I refer to that barrier as the Horn Section lol!).

    Just for the record I have a backup head, Eden WTX 260 in gig bag- but it was a marathon 90 minute set no break with those blasted horn guys as a defensive line.
    I am NO tech- but after looking at the 400+ chassis for about 10 minutes I figured even I could remove the 10 bolts and lift...
    I vacuumed about a lb of dust out with the house vac narrow needle tool, and I reseated about 3 power tubes that were starting to ride out of their socket.
    Trouble is in a house full of children and tiger wife it's impossible to repeat conditions and push it that hard for 90 minutes- but all the power tubes and preamp tubes have glow from
    Next gig I make sure the Eden is plugged and ready probably with an A/B box.

    I think I'm gonna put in all new 12ax7s in the preamp, but I just can't budget $300.00 right now for power tubes.

    Anyone else ever have this volume drop on stage with a 400+?
  2. quite possible your experiencing ear fade.
  3. nukes_da_bass

    nukes_da_bass Inactive

    Feb 19, 2006
    west suburban boston
    Then the whole band is experiencing ear fade. Had to answer the other 7 members "what happened?"
  4. Gringo Starr

    Gringo Starr

    Apr 21, 2012
    I have a Mesa 400 and 400 + and anytime I've ever had any volume / weird noise issues, it's always been tubes. Those amps are pretty simple. They eat power tubes up fast. Mesa will tell you that you can get 3 years between changes but I never have.

    I know your wallet is dreading swapping out 12 6L6's. Over the past 2 month's I had to re-tube both of my Mesa's (that's 18 6L6's my friends :eek: ) but IMO if it were anything else, the amp just wouldn't work. Hope that helps.
  5. nukes_da_bass

    nukes_da_bass Inactive

    Feb 19, 2006
    west suburban boston
    Yup! 12x6l6 was the big dread you are right!
    Incidentally, what 12AX7 preamp tube gives the cleanest sound? I play classic R&B so I'm
    Looking for a B15 sound at modern volumes...
  6. LiquidMidnight


    Dec 25, 2000
    I really can't say enough about JJ for giving you a clean, glassy sound.
  7. nukes_da_bass

    nukes_da_bass Inactive

    Feb 19, 2006
    west suburban boston
    Mmm, clean and glassy! JJ it will be TY!
  8. B-string

    B-string Supporting Member

    That B15 sound IMHO, IME comes from the octal preamp tubes. No 9 pin sounds like those octals. You can get close though. :)
  9. timv


    Jun 7, 2000
    Chandler, AZ
    If it intermittently lost volume but then when you used it again seemed back to normal, try jumping a cable from the send and return jacks.

    When those get dirty they will cut volume.

    If the problem is overall loss of volume, try preamp tubes first.
    The power tubes generally fade slowly and I honestly doubt you would hear a difference all of a sudden.

    Usually, unless a power tube blows, you really don't even know they are worn out until you put a new set in and then notice a tone/volume change.
  10. JN8642


    Aug 19, 2015
    Hi sorry to revive a thread(I knowww I'm the worst) but I've got a Mesa 400(non plus) with a similar issue to the OP's. Mine has a volume drop after a long while of playing, like an hour or two/three, it varies. My past tube heads didn't do that and the amp isn't hot, tubes look fine, no weird noises or smells either. The tubes were put in in 2009 I believe the guy I bought it from said. Just looking for some advice. I have crappy patch cables for my board(which I'm replacing), I'm wondering if that could be causing an interference maybe when I stomp on the pedal and the cable moves slightly?
  11. beans-on-toast


    Aug 7, 2008
    Sounds like the amp needs a general servicing. All metal to metal contacts need to be cleaned with deoxit. This included all jacks, including the EQ footswitch jack, scrub the tube sockets, tube pins, and clean the pots.

    Fading volume is one sign of a failing tube. The tubes need to be checked.

    If you are hearing static when the amp heats up, it could be that the tube sockets are dirty (oxidized) or require re-tensioning. There are other possibilities, a signal cap could be leaking when it is hot.

    When it happens, try setting the EQ to out and see if it makes a difference.

    All this points to service time.
    Last edited: Mar 14, 2017
  12. chaosMK


    May 26, 2005
    Albuquerque, NM
    Too much hip thrust
    I have been using a 400 as my main since 2005. Never had issues with volume drops but I always noticed that if I ran it hard for an extended period the power section would "warm up" a bit and get hairier.

    Check the tubes, do what you can to service the amp. I love taking apart that chassis with it's 20 screws.
  13. BassmanPaul

    BassmanPaul Inactive

    I would very much advise not to take the amp apart. Unless you are a tube tech with lots of experience, which the OP is not otherwise he wouldn’t have asked his questions, there is nothing inside for you except lethal voltages!

    It’s Tech Time! Sorry.
  14. JN8642


    Aug 19, 2015
    I love this head, should have it to the tech by Monday!
  15. chaosMK


    May 26, 2005
    Albuquerque, NM
    Too much hip thrust
    Don't wring your hands too much Bassman, there is not much risk involved with taking the top lid off of it. Not sure if you know the amp. I hope the following image does not make anyone nervous:

  16. BassmanPaul

    BassmanPaul Inactive

    A very wise choice my friend! :D

    In order to address the OP’s Issues it’s the bottom that needs to come off exposing the B+ to unknowing hands.
    Caca de Kick and primusfan1989 like this.
  17. mikeswals

    mikeswals Supporting Member

    Nov 18, 2002
    Seattle / Tacoma
    I've owned several of these older gems. There is one pitfall that I experienced with all of them as they had some age... the heater power wire to the preamp tubes would break at the solder joint on the circuit board and usually not expose itself until the amp was running for a long time, then loose contact making the volume disappear, then after the amp cooled it seemed to be back to normal. You can usually spot this by watching the preamp tubes as you play, if they start going dim that's it.

    Best to have the tech fix it.

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