Mesa 400+ Adding Bias?? Tubes Opinions

Discussion in 'Amps and Cabs [BG]' started by Big String, Apr 12, 2002.

  1. Looking for opinions on tubes and conversions.

    I have been reviewing several posts on the Mesa Boogie Bass 400+ amp. My main question is how difficult is it to have a bias control or controls (?) installed on the 400+? I noticed that Psyhco BG made mention of it a couple times referring to better performance etc. I might be ready to have my older one converted. I have a new one too, two, 2.

    Older Amp History (my first 400+)
    Approx: 1-1/2 years ago:
    Changed tubes to Sovtek 5881 sounded crappy and dirty. Installed Sovtek 12AX7LPS (early edition), keep shutting down (no signal, low hum). Went through 4 sets of LPS tubes and got all my money back. Took out 5881, replaced with Svet 6L6GC and Mesa 12AX7 (ECC83) have not had a problem since. Amps sounded much better. I love the Svets but heard/read the Electro Harmonic 12AX7EH were the bomb for 400+. Bought new 12AX7EH's for amp, but sort of skeptical about installing since I had so many preamp tube problems. Anyone try these in their 400+? Any problems like mine?

  2. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    If you want to improve the tone of your amp then you should install some NOS USA made preamp tubes. They are kind of hard to find but I have a source if you need help getting some.


    AMJBASS Supporting Member

    Jan 8, 2002
    Ontario, Canada
    NOS tubes can be quite expensive(though usually worth it). Before spending a lot of money on them, I would recommend trying the Sovtek 12AX7WB(not the WA!). They have a "flat" sound, and are very well suited for bass amps. I like them much better than the LPS. I feel (for bass amps), that the WB's are right up there with NOS in terms of sound quality.

    The electro-harmonix 12AX7's did not impress me too much. They have a lot of gain, but are pretty thin sounding. They seem to color the sound much more than the 12AX7WB's do. Try may like them.
  4. Mesa's choice of tubes sound excellent. I once replaced all my 4 y.o. 6L6's in my 400+ with 5881's and the difference in tone was massive and deep. "Don't mess with it if it ain't broke..."
  5. Thanks everyone, keep'em coming.
    FYI, the Svetlana 6L6GC is exactly my taste in the power section. The 5881 are a "grittier" sound and noticably less head room. Sorry, I didn't mean to say crappy about the 5881 sound, it's o.k. just not me. I have not really compared the Pre-Section yet and that's really what I'm looking for. The Mesa ECC83 (I think that's right) are a little brittle sounding, but like I said I had bad experiences changing them.
  6. Found out what part of my problem was with new 400+. The EQ swithch was stuck between on and off inside the amp. My tech found it pretty easy. I tried the new 12AX7EH in my amp and they sound great. Soooooo quiet. If anyone is interested I am willing to sell the slightly used Sovtek 5881 set of 12 cheap. Paid $10.00 each will sell set for $50.00 even. Only used for about 8 hours playing time.