Retubing Mesa/Boogie Bass 400

Discussion in 'Amps and Cabs [BG]' started by chaosMK, Nov 4, 2005.

  1. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    I think the time has finally come that I retube my 1982 Mesa/Boogie Bass 400. I got this thing in pristine condition, but with the original Sylvania 6L6 tubes. I am playing too many gigs these days to be constantly worried about having an outage irght in the middle of a set.

    What I am considering are JJ's KT-88's for the power section.

    I am not sure what preamp tubes to use. I am interested in as much clean headroom as possible and would like to have some difference between the channels- maybe to enhance/complement the subtle differences they naturally have.

    Channel 1 is suited more to active basses and is a little friendlier/smoother sounding. Before I picked up an ABY switch, I used this channel primarily.

    Channel 2 is suited for passive basses and has a slightly harder and less forgiving edge to it. I rarely use it by itself, but when I Y out to both channels, I have most of my volume coming from Channel 2 with a good dose of Channel 1 softening the edges a bit.

    Any thoughts? Or should I just go JJ all the way?
  2. Now I'm not a tube expert, but I thought the 400 came originally with 6550's...and also Sylvania stopped making tubes in the 70's methinks these aren't the original tubes...

    Time for Psycho Bass Guy to straighten us (me) out.
  3. Caca de Kick

    Caca de Kick Supporting Member

    Nov 18, 2002
    Seattle / Tacoma
    The Bass400 originally came with 6550's.
    I have one, and I retubed mine a month ago with JJ KT88's (6550's) that I got from Eurotubes...awesome sounding tubes btw.
    I have run this head with 6L6's alot, and often switched tube types depending on what I wanted (sounds nice n'dirty with 6L6's or even just 4 6L6's only). The 6550's have ALOT more volume, I have to turn my master volume down 30% from what the 6L6's do.

    I still use my CH1 for actives and CH2 for passives.

    Preamp tubes are suppose to last the life of the head, I changed mine once 14yrs ago to sovteks.

    As a side note, all mesa heads say "1982 mesa", doesn't mean they're from '82. Both my D180 (1986) and B400 (1988) have their dates written in pen on one of the caps, you remove the bottom cover to see it.
  4. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    JJ and Mesa seem to go together very well. I have JJs in my 400+. The Sovtek KT-88s seem to have a following as well though.
  5. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    Anyone know what will give me a smooth sound for Channel 1 and a harder sound for Channel 2 in the pres? Or should I just leave it up to the circuitry?
  6. Tubes don't just up and die. Especially if they're getting worn out from age, they'll give you plenty of warning. Unless your amp is acting funny, you have nothing to worry about. Is it doing anything weird?

    I'm no Mesa expert, but I seem to recall that as US made 6550's became harder to find and more exepensive, Mesa outfitted later 400's with 6L6GC's. The reduced power was why they eventually changed to the 400+ design.

    Sylvania didn't actually stop making tubes in the late 1970's. They were bought out by Philips, who moved production to Europe (what is now the EI plant) but also sold off old Sylvania stock well into the 80's. Mesa used mainly Philips tube in the early 80's, so seeing a set of stock 6L6GC's labelled as Sylvania is not a stretch. The Sylvania 6L6GC STR is the tube that Philips used for its JAN 7581- they're pretty much identical.
  7. prismacolor2


    Nov 6, 2003
    My 400+ had its original mesa branded 5881s when I first got it.
  8. Philips ECG tubes were nice :(

    ChaosMK, take your amp to your tech or someone, and have hit check the tubes, see how they are living :)
  9. zoloo

    zoloo Supporting Member

    Jun 7, 2005
    I heard the 400+ had the bias fixed and that you could only put Mesa tubes in it .
  10. Caca de Kick

    Caca de Kick Supporting Member

    Nov 18, 2002
    Seattle / Tacoma
    You know Psycho, years ago I heard this same statement once before. I wonder if Mesa made the 400 the same exact way for both versions, and simply plugged in 6L6's, or was something actually changed that someone shouldn't run 6550's in a late 400.
    I wonder this because I would love to buy another 400, and about 98% of them you see out there are sporting 6L6's because they were so cheap to buy. If something is different, I wonder if there is a way to tell, but my guess is there is no difference.
  11. Tim Cole

    Tim Cole

    Jun 12, 2002
    Findlay, Ohio
    Well, the 400 design has 6 power tubes, and the 400+ has 12 tubes. I'd say that's a big difference. :)
  12. He's talking about the 400 tho

    As far as i am aware, and am not very aware at all, but alot off ppl do it, there is no problem with putting 6550's in a 400 that previously had 6l6's

    One modification that could be made is to add bias pots to the amp for optimal performance
  13. Caca de Kick

    Caca de Kick Supporting Member

    Nov 18, 2002
    Seattle / Tacoma
    The Bass400 and Bass400+are different animals in the power tube sections...this topic is about the original Bass400 with only 6 tubes.

    I am one of those guys who does switch between 6550's and 6L6's in my Bass400 for a different sound, but I also know mine originally came with 6550's and I can safely switch.
    Psycho said this and I heard it once before, that late-built Bass400's came equipped 6L6's because 6550's were hard to find and expensive to buy, but 6L6's only make 150w where 6550's make 300w (the difficulty made Mesa come out with the Bass400+ with twelve 6L6's to make 300w again).

    So perhaps I should rephrase my question; I'd like to buy another Bass400, but if I find one is it okay to run 6550's in it because I don't know how to tell the difference between and early one and a late one, and is there a difference at all? My guess was probably no difference in the early or lates.
    I only wondered because my old MesaD180 with six 6L6's had a very similar looking power section to my Bass400, but I was told to not run 6550's in it.
  14. 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 am the second owner of my Bass 400, and the guy I bought it from said that he bought it new with 6L6's, and always ran them. It sounded very good with 6L6's, but I bought the 400 specifically for its ability to also drive 6550's (& KT-88's). But, with the fixed bias, I strongly suspect that it's not really ideal for at least one, if not both, tube types. So, my Bass 400 is currently having bias trim pots installed, and I will be retubing with JJ KT-88's. I have some nice 6L6's to try, too, and I like the fact that I should be able to dial in the appropriate bias for either tube type (and for individual brands/tubes).

  15. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    I placed an order with Eurotubes (based in US) for some blue-tinted KT-88's. Ill update when I get them installed.
  16. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    Wow, Eurotubes ships really fast. These tubes seem to be very high quality. A good amount of glass on them- they are pretty heavy.

    Anyone know where I can find information on how to check the bias on a Bass 400? I have the basic tools (a multi-sensor) and would rather look into it myself for two reasons: 1) Tube techs are few and far between in this state (New Mexico) 2) Said tube techs are very likely booked until god knows when.
  17. Im not sure, but i think the Bass 400 (and 400+ for that matter) are fixed bias

    So just stick them in, altho, for optimal performance (safest too) i'd get them modifed to have bias trim pots
  18. DavidRavenMoon

    DavidRavenMoon Banned

    Oct 20, 2004
    My 400+ had Mesa tubes in it. The preamp tubes are now Sovtec, which I feel are a bit on the soft side.
  19. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    I feel all Mesa tubes are a 'bit on the soft side'.

    MK, when you ordered those tubes from Bob, did you tell him they were for a 400? if so, you should be good to go. He knows his amps, and will send tubes to match.
  20. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    I told Bob they were for a Bass 400 and that I was after more clean headroom. They came in a sextet with "29" and a |||| symbol market on it.

    Thanks for the advice on the Sovteks in the pre. By soft, do you mean earlier breakup or just softer tone?