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Need info on tubes..

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

  1. i've got a tube-driven overdrive pedal ( Hughes & kettner tubefactor ) which has one 12AX7 in it..

    Some guy at another forum mentioned that putting a 12AT7 in it would make it sound better with a bass..

    But.. then another guy said that a 12AW7 would sound even better..

    this stuff is so confusing..

    what's the difference between the 12AX7, 12AT7, 12AW7, 12AU7, etc ??

    and.. what tubes are reccomended ? i've asked my local guitarshop and they can get Fenders, Groove Tubes, Marshall's, USA sovtek's ( $$ !! :eek: ) and russian Sovtek's..

    c'mon guys.. give me a quick-tutor on tubes here !
  2. monkeyfinger

    monkeyfinger Moderator Staff Member Supporting Member

    There is a lot of difference between these tubes. It mostly has to do with the gain structure, called Mu. The 12AX7 has the highest Mu. In other words it has high output and breaks up easily. The 12AT7 has lower mu. This tube will give you less output, but also has a warmer, milder overdrive sound. The 12AU7 is lower than that. The 12DW7, (I think that is what you meant when you mentioned the 12AW7), is a mixed Mu tube. It is half a 12AX and half a 12AU, so it has characteristics of both.

    The DW was the original Ampeg SVT pre-amp tube. Nice fat, bottomy sound. If you want less break-up use a 12AT7 over an AX. I probably wouldn't bother with an 12AU7. They tend to be used for linear gain situations like phase invertors.
  3. boobinga


    Feb 9, 2001
    Pacific NW
    Good luck figuring out tubes. Figure, seriously, several months research and listening to what people say re what's the best tube for you! Gets back to what sound you like, and how do you figure that without hearing the various tubes? And wait till you hear about NOS, etc! Also, you might want to check out the sources on ebay. Best of fortune to you!
  4. monkeyfinger

    monkeyfinger Moderator Staff Member Supporting Member

    Tubes can be a hassle if you start buying into the lore. I recently had to replace a pre-amp tube that went on me. A 12AU7. I went to my tube guy. This guy has been repairing tube amps for 25 years. Really good guy.

    So I asked him about which tube I should get.

    He said, "Look, it's not like I have the time or inclination to put my cardigan sweater on, sit back in my easy chair and smoke a pipe while I try different tubes and write comments about whether they are earthier, or smokier, or not. I just offer a decent grade tube with good reliability for the average guy and a tube with better noise specs for the more discerning types. I don't get into it further than that."

    (Actually, I bought an pair of EI 12DW7 from him once for $12/ea. Nice tubes.)

    The reality is that most good tubes will do you just fine. I like Sovteks, and some of the Groove Tubes are good even though they are Chinese.

    If you want to get crazier than that, plan to spent hours smoking a pipe.
  5. hmm.. It sounds so nice with an 12AX7.. [​IMG] i wonder how it will sound with a more warm tube in it...
  6. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    Well, I gave up pipe smoking years ago and don't wear sweaters, but...........

    I've spent a great deal of time, energy and money checking out various 12AX7's and substitutes in my tube preamps. I've formed some strong opinions about tubes and tone.

    The only Sovtek tube I've tried that sounds pretty good is the 12AX7LPS. They sound pretty good, actually, but have a reputation of being prone to be microphonic.

    Most of the Chinese tubes sound just OK when compared to NOS Sylvania, RCA, GE, Mullard or Telefunken tubes. The difference in tone is dramatic.

    Take a nice SWR amp (or preamp) and install a NOS RCA 7025 in place of the Groove Tubes 12AX7 and the gritty lower mids will be gone, the harsh highs will be sweet and the lows will be big and clear. IMO SWR equipment is not usable with the stock tubes and sounds great with great sounding older USA or European tubes.

    My ears are not your ears so YMMV. I do get lots of compliments on my tone from other bassists, however, and my bandmates love my bass rig so I believe in the tone I get.

    Another lower gain tube to consider is the 5751 which has 70% of the gain of the 12AX7. This is a very rugged tube designed to be used in tanks and aircraft. It usually sounds very nice for bass. Sovtek currently makes a 5751 but I have not tried it. I have tried both GE and RCA 5751's and they sound great for bass.


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