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Broken Boogie ??

Discussion in 'Amps and Cabs [BG]' started by Chunk-O-Funk, Oct 5, 2005.

  1. I have a Mesa Bass 400 That I have had for some time now (1985?), actually posted here that is was a 400+ a couple of times but it is older than that. Took a peak at it today and there is no + sign.

    Anywho....I have not used this in quite some time so I am describing the problem from my faded memory. Basically what would happen is, when playing and maybe pushing the amp a bit, the power tubes would glow very bright, and the fuse would blow. It would only happen when playing out, at stage volume. Not overdriving the amp, not clipping the amp. Just a moderate stage volume, the tubes would glow and out goes the sound. This would happen with either input.

    Some more facts,

    This happen in my formidable years, didn't know much back then. We just kinda plugged in and played, It was the simple years. :D 1985-1986 no interweb thingy. No Bass Player Magazine. No older, more experienced bass mentors just yet.

    This amp was only over one year old when this problem started to happen. I remember this because it was like two month out of warranty. We didn't play out a lot back then, but we did rehears a lot, so there really was not a lot of hours played through this amp or any road abuse. Always handled it myself and it was always racked. Always used the 2X15 Boogie cab that I got with this amp.

    Any clue what would cause this? Could it have been something I have inadvertently done (settings)? Was there any common problems with the Bass 400 back then?

    I plan on bringing this thing to a pro and have it check out, but would like your input. I don't think I can re-produce the problem unless it will be played at stage volume for sometime.

    I have had this amp for about twenty years and only played it for a year or so. It is in brand new conditions, so I would like to have it fixed, after having it fixed it may be for sale. Maybe not, I'm torn with what to do with it.

    Thanks, Matt.
  2. Masher88

    Masher88 Believe in absurdities and you commit atrocities

    May 7, 2005
    Cleveland, OH
    Sounds like you are describing a cracked tube. It still works...kinda, but it's sucking in outside air and eventually trips the fuse. Something similar happend to me on tour (with my 400+) Just a quick set of replacement tubes did the trick. I happened from being banged around or from excessive vibration
  3. Mmmm, Maybe? It was more than one power tube though.

    This part I'm not sure of but If I plugged into one input three tubes would glow and when plugged into the other input, the other three would glow.
  4. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    It might be a loose power tube. I blew a fuse warming up for a gig once cause of that.
  5. tadawson


    Aug 24, 2005
    Lewisville, TX
    This could also be something in the bias circuitry that is changing when hot - like a cracked resistor or similar, that is causing excessive current in the tubes when it gets hot . . . . since he said that all tubes are doing it, then I would suspect the problem to be in the bias/driver stage, or possibly the output transformer area.

    - Tim
  6. the 400 and 400+ are both fixed bias, but yeah, sounds like something is trying to push them harder than they should be going

    If one power tube is dead i think stress gets put on the other tubes and they try to overcompensate ? i could be wrong

    just take it to a tech :p
  7. tadawson


    Aug 24, 2005
    Lewisville, TX
    Fixed bias or not, the bias circuit can still develop a fault . . . . Boogies are biased, IIRC, by a pair of resistors. If one should fail - foom! And you CAN tune bias in a Boogie - you just have to replace parts instead of using a pot . . . .

    - Tim
  8. winston


    May 2, 2000
    Berkeley, CA
    I had a Bass 400 that blew fuses when pushed hard. It was only a problem with inefficient cabs. When I ran it through SWR Goliath III Jr. 2x10 and SOB 1x15 cabs, it got stupendously loud at low master settings and never blew a fuse. It happened with different tubes so I suspected the problem was in the circuitry.