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Repairs and Tubes

Discussion in 'Amps and Cabs [BG]' started by JJd2sc, Dec 18, 2005.


  1. JJd2sc

    JJd2sc

    Jul 31, 2003
    Marietta, Georgia
    Recently, my Mesa 400 decided to blow its fuse, then start smoking. I quickly turned it off and replaced the fuse, then turned it back on. Same thing. In retrospect, it was a bad idea to turn it back on, but I guess you live and you learn. I took my amp to a local guitar shop, and the staff looked at it and sent me to a more experianced repair store.

    After talking to the guys at the second store, he said it seemed like a strong electrical current went through the bass and literally incinerated some connectors inside the amp, and also fried a tube. He said the repair will cost ~$150 dollars, including maintenance. That price will work for me, but then the confusing stuff comes in. Tubes are apparently like christmas tree lights, and if you blow out one of them, the bias of the rest will be off, etc. The guy on staff told me I would need to replace my whole set of 6. This caught me as a sales ploy until he said I could always order the tubes directly from Mesa and then bring them in rather than the store ordering it and marking it up.

    Here is where the questions come in. He told me some Mesa 400s are wired for 6L6 tubes, and some for 6550s. What I remember from when i bought this amp, the owner said he replaced the original tubes with 6L6 tubes, making me think there used to be 6550s in it. What the staff told me was its impossible to just change tube types like that without a lot of work done, and the amp would sound terrible and weak with the wrong tubes in. He gave me some numbers and the serial number from my amp and said that if I called Mesa they might be able to tell me. Should I order tubes only from Mesa? Or could I get the right type from a most likely cheaper source? The biggest question I have is if all this information is correct. Does anything they told me sound like its a money scheme or just incorrect information? Thanks in advance, sorry for the long read.
     
  2. jeff62

    jeff62 Supporting Member

    Oct 24, 2005
    Orlando, FL
    Calling Mesa to confirm is the easiest thing to do. I know for a fact that, at least in their guitar amps, Mesa makes the amp to accept a number of different power tubes to allow the owner to get slightly different sounds. Of course, they recommend that you use their tubes.

    I would be surprised if they made their bass amps to accept only one type of tube. Doesn't even make sense if you think about for too long. ;)
     
  3. I know there are some 400 owners on Talkbass who could give you an answer on the nature of the amp itself. Maybe a search would turn up some names, I can't think of anyone but I know the 400 and power tube types has been discussed. Most people would agree that if you are going to retube Mesa brand is not the best choice, and if you have Mesa tubes in there now even if they're not "bad" the amp could sound better with another brand. People seem to like JJ tubes, but there are other brands too, and most cheaper than Mesa.
     
  4. Call Mesa, and then go to a shop that knows what their talking about......

    I changed out the 6L6s for 6550s on mine, and bought it used, not knowing it's history....use medium-range tubes....
     
  5. JJd2sc

    JJd2sc

    Jul 31, 2003
    Marietta, Georgia
    How long has your amp been running with the 6550s? Does it sound better than the 6L6?
     
  6. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Calling the good folks at Mesa Boogie would be a great idea. They were more than happy to answer my questions about a Mark IV guitar amp that I recently bought.

    I've seen burned up connectors in Mesa Boogies before...

    It's probaby best to use a matched set of power tubes...you won't need to replace power tubes that often so you might as well do it right, have the amp be as good as it can get after the needed repair and then you'll have one less worry when you're playing bass.

    While one could probably substitue power tubes within reason, it seems like a real good idea to me to stay with the ones (be they 6L6s or 6550s) that the amp was originally designed for. Preamp tubes are a different story but power tubes have very specific plate voltage ratings (6550s being higher), current draw and heater current draw... The power and output transformers in high power tube amps are very expensive so it's not worth the risk of damaging them...
     
  7. Eric Cioe

    Eric Cioe

    Jun 4, 2001
    Missoula, MT
    I'm fairly sure that Bass 400s run 6550s and have 6 of them (300 watts), and the Bass 400+s run 6L6s and have a dozen (also 300 watts). I could be wrong, but this was always my understanding.
     
  8. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    You can use either tubes in a 400 without any difficulty, and I suggest that you talk to your tube vendor about ordering a matched set that's designed to work with the bias of your amp. I'm not a fan of Mesa tubes, but almost any good tube guy can match to their specs. I believe Tom Bowlus had a bias adjustment installed on his to be able to adust the amp more precisely for the different types of tubes.

    It probably is a good idea to change out the full set at once while you're mucking about with the amp anyway. Keep the old ones that are still good as backups.

    The way the tube amp works isn't like christmas lights at all, but the tubes are usually set up in pairs, so if one goes, you might harm a second tube, if the fuse doesn't blow quick enough.
     
  9. Check out this thread.
     
  10. JJd2sc

    JJd2sc

    Jul 31, 2003
    Marietta, Georgia
    thanks a ton guys, this really helps. Guessing right here... the 400 has 2 power tubes and 4 tone tubes? I think im going with JJ tubes, and suggestions as to where to go from there?
     
  11. All six 6550 or 6L6GC's are power tubes. There's no such thing as a 'tone tube.' Get your tubes from Eurotubes.
     
  12. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    I did, and I recently got mine back from the shop. But, I don't know if they "fine tuned" it for me yet or not. If they did, then something else is not right, because the tubes (now KT-88's) are overdriving way too soon (with very little volume). :confused:

    Tom.
     
  13. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Sounds like they have it set up like a guitar amp...
     
  14. Tim Cole

    Tim Cole

    Jun 12, 2002
    Findlay, Ohio
    No, there is some serious bad mojo going on with this one.
     
  15. cheezewiz

    cheezewiz

    Mar 27, 2002
    Ohio
    Yep
     
  16. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    I'm hopeful that it is an easy fix. But if not, it'll be on their dime, this time.

    Tom.