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400+ woes- very distraught

Discussion in 'Amps and Cabs [BG]' started by Foxworthy925, Feb 21, 2008.


  1. Foxworthy925

    Foxworthy925 Guest

    Feb 24, 2007
    Bay Area, CA
    So lets see. I've had a 400+ for a while, and was pretty happy with it. I've searched many threads on tube replacements and such, and got a lot of good help from one of Psycho Bass Guy's threads. I was looking for a preamp change so I went with some Tungsol 12ax7s, and a NOS (american made) Tungsol 12au7. Put 'em all in- amp didn't work. Through process of elimination, I discovered a bad tungsol 12ax7 that was causing the problems. Good thing I ordered one extra, just in case.

    So lets see...12au7 as the driver tube of the preamp, the other three slots filled with the new production 12ax7s. When I first started up, there was an enormous volume difference- absolutely no volume at all (figuratively speaking). I let it warm up a bit more, and after a couple of minutes, everything was great. Normal volume, absolutely beautiful tone, very happy results. I assumed this would be the norm, that I'd just need plenty of time for the amp to warm up before it would be at normal operating conditions.

    I went to band practice the next day- not good. It was a very laid back practice since the drummer could only be there for less than an hour, so I ended up spending a lot of time just chilling and playing at pretty low volumes. The amp did the same lame no volume thing for hours and hours on end. If I tried to turn it up to a good volume, it would distort like crazy before being anywhere near the correct volume. This is at 4 ohms going into a 210 and 115 btw. There was a break for about an hour after about 3 hours of uselessness. I went out and fired up the amp again- in under 15 minutes, it was back to magical wellness (or atleast close enough if not perfect).

    Practiced again a few days later- same gay **** for a while, but became normal after probably half an hour. Now it becomes last friday (15th), and it's the afternoon before my first gig with this death metal band I joined. Gave the amp plenty of time before hand, but it still pulled similar crap- just being extremely finicky. So I ended up using a hartke 3500 that I hadn't sold yet, for the gig. Pretty lucky I haven't had a buyer for that amp, and just happened to still have it at this time. It actually sounded pretty decent for the show, though I would have LOVED to be able to use my mesa instead.

    So now I'm here whining about my finicky mesa, when you all are thinking that it's clearly just a problem because I put the 12au7 in the driver stage of the preamp. Well, yeah, I'm gonna swap that out and see if it fixes everything, but I'm still very unsure. Before any of this trouble, I loved the way this tube amp sat in our death metal mix, but I've never been completely absolutely blown away by the tone. In a softer rock setting, I was constantly battling with a lack of lows that I wanted, and that honky upper mid characteristic. Tone aside, this amp has always seemed a bit finicky for me. I'm wondering now if I'd be much happier with a nice reliable hybrid amp, or other solid state driven device. Maybe my inner gas is just urging me to try my possibilities with other all tube amps, because I'm really itching to try some type of svt. But maybe I would just be better with a racked ss amp, that I wouldn't ever have to worry about. What's everyone's opinion?
     
  2. sunbeast

    sunbeast Supporting Member

    Jul 19, 2006
    Los Angeles, CA
    Obviously it makes sense to back track and try replacing the preamp tubes one by one with the old ones to see if thats the problem- seems likely to me if thats all that you changed. If you were never very happy with the tone, you might want to consider a different set of power tubes- the stock Mesa-branded Sovteks were crap to my ears when I first got my 400+. I replaced them with some comparitively priced Shuguang 6L6GCs and now it is a monster of tone and louder as well- certainly no shortage of lows! Just make sure you order power tubes from someone who can send you a set properly matched to a 400+- ie Eurotubes or Lord Valve, etc...since you can't bias Mesa amps. Replacing the power tubes will cost at least $130, but that is one thing you'll have to accept if you choose to keep a tube amp. My 6L6s are still running strong after a year- may be good for another year or two if I'm lucky!
     
  3. Foxworthy925

    Foxworthy925 Guest

    Feb 24, 2007
    Bay Area, CA
    Huh, I knew the 400+ had a set bias, but I thought it was just a matter of a good tech opening her up and adjusting it. I am also considering finding a tech in my area who can instal an adjustable bias so I can save some trouble with the power tubes' short lives.

    So I'm thinking to myself that I have two options...
    - Getting my amp serviced by a good tech, possibly getting the power tubes changed (if it will better suit my tone desires), possibly getting an adjustable bias installed, and getting a nice shock mount rack (because I desperately need one).

    or

    - Ditching tube amps and going solid state, even though I do love how this amp sits in the mix (well, sat I guess, before all this trouble started).
     
  4. Frankie Fender

    Frankie Fender Supporting Member

    Well you said that the amp always seemed finicky to you before the tube swap. Maybe you should get it looked at by a pro? I once had a blown resistor on an SVT II and didn't even know it til I brought it in for a routine checkup. My Mesa has been strong for a long time and what you are describing is not a healthy amp.
     
  5. Yes a good check up would be in your best interest. Let me know how the adjustable bias installation goes. That would save a lot of re-tubing hassles.
    Has anyone else had this done. Is it costly or does it devalue the amp? Curious minds wanna know.
     
  6. Foxworthy925

    Foxworthy925 Guest

    Feb 24, 2007
    Bay Area, CA
    It would be great if he himself would post, but I know that tb's anderbass has done the adjustable bias mod. Here's the link to a thread that he talks about it in (scroll to almost the very bottom of the page), which is where I've gotten all the inspiration for these 400+ mods:

    http://www.talkbass.com/forum/showthread.php?t=387202&page=3

    It'd also be great if Psycho Bass Guy would see this thread, because I know he's very knowledgeable with tube amps in general, and is where I first heard about the 12au7 in the preamp mod.

    I really do love this amp and don't want to give up on it, so I think I will definitely have a tech to a huge run down of every last inch of everything to work out these quirks.
     
  7. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    As far as your low-volume issue goes, I think sunbeast nailed the problem to one (or more) of your new preamp/driver tubes just being defective. (maybe your box got slammed around and they all were somewhat damaged in shipping)

    Psycho did recommended using Chinese 12AX7's, so if ya still got yer origanal Boogies throw-em back in.

    I dont really have much to add about the adjustable bias mod, but I do think its well worth doing all three of the things Psycho suggested for this amp. Mines still working fine and giving my SVT-II some serious competition as my favorite amp of choice.

    Hang in there Foxworthy, Try out some of your old preamp tubes first and let us know whats up.
     
  8. Vanni

    Vanni

    Sep 15, 2003
    Milan, Italy
    Me too. The mod is cheap (at least, with my technician)...
     
  9. Foxworthy925

    Foxworthy925 Guest

    Feb 24, 2007
    Bay Area, CA
    Is an adjustable bias mod a common thing to do with tube amps that are normally set bias? I'm just wondering, if I bring up the idea with a tech who's going over my amp, whether he'll know exactly what I'm talking about and be completely fine with it, or if he'll be in the dark and I'll have to walk him through it. Anyone?

    PS, I think I'm having band practice tomorrow (amp's still with all our other gear), so that's when I'll be able to get it back and do some preamp tube swaps. I'll keep you guys posted.
     
  10. Foxworthy925

    Foxworthy925 Guest

    Feb 24, 2007
    Bay Area, CA
    ^anyone?
     
  11. Tim1

    Tim1

    Sep 9, 2005
    New Zealand
    The 400+ is a great amp.I have owned many tube amps and this is my keeper. Take it to a tech and I am sure they will sort it out. A good tech should be able to fit an adjustable bias. If you don't want to go that way get a full set of tubes from Eurotubes or (I think ) Lord Valve. These companies will custom fit the tubes to suit the fixed bias of the 400+.
     
  12. Vanni

    Vanni

    Sep 15, 2003
    Milan, Italy
    +1
     
  13. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    This Job should be easy for any tech that truly understands tube amps. I'd call around first and if they dont sound completely confident about performing the the adjustable bias mod, keep looking.

    You should find quite a few Mesa adjustable bias comments in this search:
    http://www.google.com/custom?domain...;S:http://www.talkbass.com;LP:1;FORID:1&hl=en

    If ya dont already have a good Tech, you may find someone in this search:
    http://www.google.com/custom?domain...;S:http://www.talkbass.com;LP:1;FORID:1&hl=en
     
  14. Foxworthy925

    Foxworthy925 Guest

    Feb 24, 2007
    Bay Area, CA
    Once again anderbass, you have been extremely helpful. Thankyou

    And thanks for every one else's help- I won't give up on this amp.

    One other question: would a tech be able to spruce up my power chord on the amp a bit. Mine's one of the ones with the permanently attached power chord, and I just feel a bit uneasy that it is able to be pulled out a bit (so the base that is sticking to the metal box lifts up a bit). Probably nothing at all, but I'd like a lot of these little things checked out...
     
  15. Stromrider

    Stromrider

    Feb 16, 2008
    CT, USA
    You may need to replace the grommet holding the power cable into the amp. Find an older tech thats willing to take his time and look everything over, and one that listens to you. Any worthy tech will beable to add an adjustable bias control. Their are alot of hack-job techs around, so if you can, take a look at his shop, if its a complete mess and unorganized think twice about leaving your amp with him.

    Good luck.
     

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