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replacement tube for SWR pre-amp?

Discussion in 'Amps and Cabs [BG]' started by KB, Jul 7, 2002.

  1. KB


    Jan 13, 2000
    Chapel Hill, NC
    I am considering a new tube for my SWR SM500 amp. Yes I have searched the boards, and I see many different opinions on many different amps. I am looking for the SWR SM-500 (400S) pre-amp in particluar.

    The SWR has good sound with the stock GT tube, but I want something with a little more pronounced mids and maybe something to reduce the bright "SWR" highs just a little. I like to have a very pronounced sound in my band as I play a lot of lead melodies so I don't want to be too transparent or too muddy/mushy (I still want clean articulation with the slight growl of pronounced mids). Also my basses (two G&L L2000s) are very low end heavy so I need to be careful and not get something that would get too boomy. I also want to keep noise levels fairly low if possible

    I have heard that the Electro Harmonix 12AX7 has this ability, but I also wanted to know what the other options were. Maybe the JAN Phillips 12AX7WA? Please advise as I am a tube novice.

    Also I assume that changing the tube is just grabbing it and pulling it out (when cool) and popping the new one in its place. I know there is no biasing, etc. is there anyting else i need to be careful of?


  2. You can swap the tube very easily and will not damage the amp. You won't break the bank by trying different kinds. I'm shure other people will tell you which brand they like. The difference in sound may be subtle but the best way to check how good a tube is is by listening to it.
    Rock on
  3. I put a 1950s RCA 12ax7 in my sm400s and it sounded nice, until I discovered the tube to be microphonic.
  4. jasonbraatz


    Oct 18, 2000
    Oakland, CA
    i really like Ei's or JJ/Teslas in SWR stuff. i almost like the Ei's a little bit more (sweeter top end IMO) but they're not that reliable.
  5. JRBrown


    Jun 21, 2000
    North Carolina

    What was your conclusion in your search for a better tube?

  6. KB


    Jan 13, 2000
    Chapel Hill, NC
    JAN Phillips 12AX7WA was by far the best sounding tube. The Ei Elite 12AX7 (gold tipped) was 2nd best, but the JAN Phillips is really rich and full sounding. Unfortunately they are becoming rare.

  7. Ok - prepare for some rambling! I'm really on thin ice here.

    My problem is the upper midrange of my sound. I play a stingray5 through a SWR bass750/goliath, and I love the sound most of the time, but sometimes there's this midrange that is just too hard and forced. It's hard to explain, but it's the midrange that gives the tone it's vocal character and most expressive part of the sound; the part that really comes through when you play close to the neck and dig in. DR Hi-Beams are especially good in bringing these frequencies out, and Marcus Millers tone is full of it. So I'm not trying to get rid of it, just trying to "open" it up and make it sound more natural/musical/airy and not so hard and squashed. EQ is not the answer beacause I want the midrange, I just want it to sound sweeter, more relaxed.
    I've recently switched the tube in my SWR (a sovtek 12ax7WA) with a Groove Tube 12ax7A, and got a more fat bassy sound, but I still have the somewhat hard upper midrange that I was trying to mellow out. Is there another tube I might try (maybe the Electro harmonix 12ax7EH or the Ei?) that has a more open and natural midrange than the GT? (And could it be that my GT, which I thought was a American NOS, is a relabelled chinese 12ax7A as the tubestore website implies, and hence not a good example of what a good tube could do?)
    I'm not even sure if it's another tube I need, or if it's just my amp or bass (I'm totally sold on the stingray sound so I need that one) or...? I've considered getting a Demeter 201 (there's an unused older version at my local store - any difference over the new version?) or the Alembic F-1X instead of my SWR. Could any of you compare these? I know about the Basstasters.com (great site!) but it'll be nice to hear some real world comparisons.

    Thanks reading so far...
  8. xyllion

    xyllion Supporting Member Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Tough call. Tubes can change your sound. So, can adjusting the eq controls. However, after all the tweaking is done, you may still never achieve the sound you are looking for.

    If I were to make a recommendation, I would guess a 12AX7LPS. They have a fat bottom and tend to deemphasize the highs and mid-highs. Personally, I like the sound of the 12AX7EH (Electro-Harmonix). I have had good luck with them.

    Best I have ever heard was a Kern IP-777 preamp with US tubes in it. I owned it for a few months and just loved it. I later sold it though because I had too much money invested in it compared to the rest of my gear. I'm not sure I made the right choice though because that preamp really was good.
  9. A Mullard 12AX7(ECC83) will emphasize the midrange a Telefunken will smooth things out a bit more. Any USA NOS 12AX7(7025)will also work.
  10. When I bought the Groove Tube 12AX7-A I thought it was a relabelled USA NOS. If it is, I'm not sure tubes are going to help me here (it's clearly better than the sovtek 12ax7wa, but didn't fix the midrange problem). But due to the Tubestore.com info (see above) I'm thinking that my GT is a relabelled chinese tube, and hence doesn't do justice to the tube-changing game.

    Well, is there any tonal difference between the sovtek 12AX7LP and the LPS? (the LP is pretty cheap here)
  11. Jim Dombrowski

    Jim Dombrowski Gold Supporting Member

    Jan 16, 2002
    Colorado Springs, CO
    Yes, tubes can vary the sound a bit, but not much. I would suggest trying some other amps and comparing them to your SWR. I don't think you mentioned what speakers you're using. A lot of amps and cabs have a inherent sound or tone that can't be easily eliminated. Don't buy a new preamp without doing a number of A/B comparisons with your current gear. It would suck to buy a new preamp only to discover that the tone you don't like is in your cabinet.

  12. Finger Blister

    Finger Blister

    Jul 8, 2003

  13. Thanks guys. I'll do some experimenting. Today I'll try out an older version of the Demeter 201.
    Finger Blister, the tube that came with my amp was a Sovtek 12AX7WA, and the one I bought is a Groove Tube 12AX7A. It doesn't resemble the one you posted a picture of.
  14. Thats a GE 5-star 5751, 5751's have only 70% of the gain compared to the 12AX7. Good if you have a combo guitar amp that likes to squeel.
  15. Now that your mention demeter:

    I also wasn't quite satisfied with the Hughes and Kettner BB600, so I got the used demeter 201. I must say that now I'm happy. H&K seemed too clean and a bad sounding bass sounded bad through it. That's where demeter steps in. It really wakes up the sound and I love it.

    Let us know what you've found out.

  16. Finger Blister

    Finger Blister

    Jul 8, 2003
    In my SWR, no noticable loss of gain whatsoever.

    But I'm sure that you have plenty of experience with the use of the 5751 in SWR preamps, right?
  17. I would agree, I've used 5751's quite a bit and can hardly tell any difference compared to 12AX7's.
  18. So there's no difference in sound either?

    Well, I've managed to try out an older version of the Demeter 201. While it's a very nice sounding amp (the low-end is a bit more "tubey"), I must say that I don't think the sound is vastly different from my SWR, and it didn't cure the mid-range thing. Funny thing is that it had 12AX7A's in it as well. Don't know if they're the same tubes though. They weren't groove Tubes. I think I'll try a 12AX7LPS to see if it helps. Otherwise I may start testing cabs, but thats a slow process.

    Thanks for you help and info guys!
  19. Jon Burnet

    Jon Burnet

    Jan 21, 2001
    Memphis, TN
    i need to revive this one from the dead. i am looking for a tube that not only tames a little of the highs but also will get to a higher gain before poopin out. thanks for your help guys.
  20. Finger Blister

    Finger Blister

    Jul 8, 2003
    Your not going to get any more gain then a
    12AX7 or 7025.

    I also wanted to smooth out the high end "bite"
    of my SWR preamp. It was a little too 'sharp.'
    The best you can do to cure this via Tube replacement is with a NOS 5751.

    I've been using Sylvania NOS JAN 5751
    and GE 5 Star 5751 in my SM 400-S for the past 5 years with excellent results and the same gain as the stock GT "select" 12AX7-A.

    You can find them on E-Bay for around $10 ea.
    They are worth a try, especially in a SWR circuit.

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