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Mesa/Boogie bass 400 non-plus problems.

Discussion in 'Amps and Cabs [BG]' started by ironbullen, Jul 13, 2014.

  1. ironbullen


    Jan 7, 2008
    I recently went to the studio to record some tracks and i used my mesa head. All of a sudden something started to smell real bad from the amp and when i checked the back three tubes where dead and a fourth shut down as i looked at it so i turned it off. I did a very big mistake when i powered it up, i forgot to plug in the speaker cable, and the master was turned up as well. I haven't tried to power it up again. What might have happened? Is it worth trying with new tubes of have i screwed it up completely? My biggest fear is that the power transformers are fu#ked up.

    The amp was working the whole time, i wouldn't have recognized it if it wasn't for the smell. Im very thankful for any help and answers!
  2. ironbullen


    Jan 7, 2008
  3. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    You may have to replace the power tubes- at least the ones that look bad but possibly all of them.

    It is possible that some of screen grid resistors got blown too. That was probably the smell. If you take the chassis apart and look under there, take a look at the screen grid resistors (they will be hanging out on the undercarriage thing where the tubes go and on mine they look like small cubes). Cheap fix- those parts cost nothing and you can do it yourself if you have a little savvy.
  4. ironbullen


    Jan 7, 2008
    Allright, thanks for the reply! So no risk that the powertransformers are broken then? I've heard that it's really really bad do run a tube amp without any load, but at the same time it sounds pretty weird that an expensive amp like that would be history just because of a mistake that's so easily done.

    I know a local guy who's very good at fixing amps and cheap as well so i thing i'll ask him :)
  5. Power transformer is not the worry. Output transformer is the worry. Take it to your "local guy" and don't take the chance of further damage by DIY. Doesn't matter how "expensive" an amp is when you have very high voltages with no where to go (no load attached to the amp). I don't remember off hand if the output jacks short with no plug inserted, many makers do this to protect the output transformer. With the output shorted only the tubes and a few resistors may suffer from user brain farts.
  6. ironbullen


    Jan 7, 2008
    Okey! Does the tubes shut down like this when an output transformer has been damaged? And why didn't the fuse blow? Either way, i'm pretty sure this happened cause of my mistake and is not just a coinsidence. And if the output shorted to protect the amp, it sure didn't work cause something went really bad. So maybe mesa amps don't have that kind of protection. Guess the only way to know for sure is to let someone take look at it, just wanted to check first if i need to prepare myself for throwing it in the garbage dump or not.
    God i hate myself, this is the best amp i've ever tried and i got it dirt cheap as well....
    Last edited: Jul 14, 2014
  7. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    I recently had a vintage SVT smoke a power transformer. How much smoke was there and how bad was the smell? Tubes could have popped because the transformer blew first. Or maybe they just popped because of no load.

    Take it to your buy and explain what happened. Ask him to test the output tranny first. That way you're not wasting money on new tubes for an amp with a blown transformer...
  8. One thing that is opposite between tube amps and solid state amps - if you put a dead short on a solid state amp it is likely to blow the amp ... and with a tube amp, a dead short is fine but having no load at all can cause the output transformer to arc high voltage and short itself out (which would probably then cause your tubes to burn out) .... but there are other things (caps most likely) that can cause your tubes to burn out like that.

    Some old tube amps had output jacks wired to give a dead short if a cable wasn't plugged in (remember a dead short is good - wide open is bad). I kind of doubt the Mesa has that since it has several output jacks for different impedance so not so easy to do.

    Anyway ... did you have the volume turned up high and you were banging away on your bass wondering why there wasn't any sound? If so, it's possible (likely) that you blew out output transformer. But a bad cap could also cause your tubes to burn out and a bad cap is very cheap to replace if that's what it was.

    If you only turned the amp on and didn't send any sound to the amp, I don't think that would burn your transformer.

    I hope you didn't blow your tranny ... but it kind of sounds to me like that is what you did.
    Last edited: Jul 14, 2014
  9. If you discover you toasted your amp - I have a 400+ that is too much amp (too heavy) for me. Sounds like pure gold but sure is heavy to get up and down the stairs .... oh, I just noticed you are in Sweden ... nevermind.
  10. ironbullen


    Jan 7, 2008
    I talked to the mesa support staff and they said that the transformer might have been blown as well though it migh just be the tubes that need replacement. I'll check with a technician as soon as i can afford it. It needs some tender love anyway since the previous owner said he had not got it checked for a long time.

    @Rickenbackerman: It smelled quite much but not extremely much either. No smoke, at least not what i can remember.

    @AndyPanda. You're probably right, since the mesa staff told me that there might be damage to the transformer then i guess they don't have that kind of protection. I had the volume turned up, i realized my mistake cause there was no sound when i played. Thanks for the offer about your 400+ but as you say sweden is pretty far away :)
  11. You need to hook me up with a nice Swedish lady and I'll come over for a visit and bring the 400+ :) I've always wanted to live there - need a muilti-instrumentalist in your band?

    Best of luck ... I hope you find it is something simple like a cracked tube or bad cap or resistor.
    Last edited: Jul 15, 2014
  12. Best of wishes your way. I have seen many cases of older worn tubes taking the hit before the OT failed. When the tubes go they can take some resistors with them which smell pretty bad. Usually the OT won't smell if they punch through, just pop the fuse from the short.
  13. By punch through you mean arc internally.

    So if the fuse is intact it's probably relatively minor cost for toasted small parts.
  14. Yes If the HV fuse which is usually internal on the amp has not blown the trans should be fine.They usually short when they pinch through (arc) not go open.
  15. Razman


    Feb 10, 2005
    Orange Park, FL
    Iron, did you ever get this figured out?

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