should i change the preamp tube in my SS amp? [swr 400s]

Discussion in 'Amps and Cabs [BG]' started by bovine mind, Jan 8, 2009.

  1. bovine mind

    bovine mind Guest

    Jun 17, 2008
    San Francisco
    hail, trying to wait patiently until i've got enough to afford an all tube amp but get the best of my solid state.

    my overdrive [ hematoma ] is thinner and harsher than i'd like, i'm looking for a more full bodied, punchy high gain nast grit when i turn it on. i'd like my clean tone to be a bit more throbbing and warm as well. i play through a stingray 4 and think it could really benefit from some high quality tube play. i'm looking for that bob weston/shellac / throaty gravel sound. style of play is varieties of metal.

    i think my amp was manufactured sometime in the early 90s, and i don't know if the tube inside has ever been changed, i bought it used.

    how exactly would i install it? if it requires navigating through a potentially hazardous mess after removing the case i'd rather not bother and hold out until i can afford an all tube amp.

    the local guitar shop suggested a 12ax7 mullard tube. any thoughts on that tube with this amp? i've been told there it's kind of a wildcard installing tubes with different amps. would changing the stock tube really make a difference? i found a thread that described some of the benefits of different tubes with the 400s but nothing on how to actually get inside and install one.
  2. SanDiegoHarry

    SanDiegoHarry Inactive Supporting Member

    Aug 11, 2008
    San Diego, CA
    you want growl out of an SM400? Good luck. That amp was designed from the ground up to be CLEAN. I wouldn't mess with the tube at all; I'd look at other pedals or maybe a different head altogether. And yes, I've owned multiple SWR amps. Great for clean funk/slap - but a bit sterile (hence my purchase of an Ashdown to replace my SM900)

    good luck
  3. bovine mind

    bovine mind Guest

    Jun 17, 2008
    San Francisco
    yeah, it seems i can't get away from that hospital tone. i bought the amp in desperation after something went wrong with my previous SS. the hematoma is pretty excellent in itself.
  4. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
    How is your EQ set?
  5. Bardley


    Nov 16, 2007
    Louisville, KY
    I changed the tube in my SWR SM-500 that I used to have to a Tung Sol and it did improve the sound. Gave me much more mids and it sounded fuller with more gain. It's not hard. Pop the top and plug it in. Takes like 5 min.

    You will not get any grind from that amp but it can sound fuller.

    It's also not very expensive. Check out Look for 12ax7 tubes.
  6. bassninja7

    bassninja7 Guest

    Mar 1, 2008
    Napoleon, OH
    did anyone else see the title?

    tube preamp for his SS....

    its not SS it would be a Hybrid
  7. I used a Ravens Lab MDB-1 to run effects "side chain" and get the full bass sound out of my SM-400s or Bass 750s while using effects. On the SM please turn your treble to say 10 or 11:00. In fact try the rest flat and the treble at 11:00 with little to no aural enhancer. I did like up to 11 on that but no more, it cuts out so much. I found that the Hematoma sucks a lot of lows. Trying to dial that back in is near impossible and can sound contrived.

    If you can get your sound from the SM-400 just minus the grit I can suggest some other things.
  8. What cab(s) are you using? What bass? What strings? Thanks.
  9. T-Bird

    T-Bird Guest


    IIRC, Steve designed the pre by using the Russian GT labeled 12AX7, that was perhaps the most commonly available tube ATM. Any other tube may or may not sound "better". Certain circuits are more responsive to the tube change than others, IME SWR is not. It sounds pretty much the same with any quality 12AX7 tube.

    I tried several tubes in my ST220 and IIRC it was a EH long plate that I left there.

    I do agree with everyone else though, there's not much that can be done with the "SWR sound". Good/bad, well that's for You to decide.

    Pre-tube swapping is easy and relatively inexpensive if You stay away from the rare NOS tubes. I tried one Mullard in mine and couldn't tell the difference.

    A word of a warning though. Tube swapping = highly addictive ;). And when You find the "tube of Your dreams", buy another one as a spare. Since pre tubes can electrically last a fairly long time (from 10 years to infinity really), chances are that You won't be able to buy a similar one when 10 years has passed.

  10. Mo' bass

    Mo' bass

    May 4, 2000
    I tried 3 different tubes in my Mo' Bass (EH, JJ and Tung Sol). I prefer the Tung Sol because its cleaner, fuller and has nicer highs. For 'growl' maybe you can try the JJ. Good advice on cutting the highs a litte bit on the preamp. I think a bit of mid boost around 250Hz can also help you.
  11. seansbrew

    seansbrew Supporting Member

    Oct 23, 2000
    Mesa AZ.
    I put the same one in mine, it improved the amps midrange.

    For people looking to change tubes in their SWR amps keep in mind the changes are very subtle.

    I tried about six tubes out and the tung sol was the best to me. Most of the tubes I tried gave no discernable difference in audio.