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Discussion in 'Amps and Cabs [BG]' started by avvie, Feb 3, 2013.

  1. avvie


    Oct 12, 2010
    Maui, HI
    I'm sure that this is probably available in a forum search, but how many results would I get from "preamp tubes"?

    I have heard somewhere that tube model number reflect a change in sound... i.e. a 12AX7 is cleaner than a 12AY7...as though a 12AY7 tube might break up when the gain is pushed.

    Has anyone tried changing their preamp tubes to a "grittier" one and how did you like the result?
  2. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion

    Aug 25, 2010
    The Great Midwest
    The numbers correspond to the amount of gain of the tubes:

    12AX7 (gain of 100)
    12AT7 (gain of 60)
    12AY7 (gain of 45)
    12AU7 (gain of 19)
    So what does this mean? – If your device calls for a 12ay7 and you replace it with a 12at7 you will get more distortion or your device will be louder, the reverse is true if you replace a 12ax7 (gain of 100) with a 12ay7 (gain of 45) your device will be about 55% quieter
  3. avvie


    Oct 12, 2010
    Maui, HI
    Ah! thanks for the quick reply! So if my amp is factory loaded with 12AX7 then it's not going any louder or grittier then, right?

    Not that it matters... I was just curious.
  4. 1958Bassman


    Oct 20, 2007
    Some of these draw more current than others, too. The 12AT7 draws/handles more, so it's not always a direct-replacement and the reason for changing needs to coincide with the best choice. If you want to increase headroom and stay cleaner, the 5751 is one of the best replacements for 12AX7. If your amp was designed with the 12AY7, like the Tweed Bassman, using a 5751 won't change much but using a 12AX7 makes it roar.
  5. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If you want more distortion, you want to overload the input of the 12AX7 tube. You can do that by adding another amplification stage in front. Some so called high gain amps do this with another 12AX7.

    Depending on your amp, the 12AX7 stage might be able to be modified to provide more gain. A simple option for you is to add an effects box. Instrument -> effect box -> amp input. I use a Bass VT pedal to do this but there are tons of distortion pedals out there. Check out the effects newsgroups on TB, in particular this thread has a lot of info.
  6. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion

    Aug 25, 2010
    The Great Midwest
    I think you are better off buying a distortion pedal than trying to achieve it with a single preamp tube that tube distortion sound everyone covets has a lot to do with the amps power tubes. I have a Meatsmoke Preamp and even though it has three tubes and sounds incredible it still isn't like having a SVT.
  7. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    I have done this in a number of bass amps and guitar amps. It may depend on the amp, but these types of changes have made the desired difference every time. I've put low gain tubes in some amps (JAN 5751 specifically) to lower gain/keep things cleaner, or higher gain 12AX7's (specifically JJ EC803 "long plate") to allow earlier breakup in amps that were too clean or had clean sections that I found too sterile.

    An extreme example is my Buster Bass which came with all low gain tubes in the preamp (5751's, even a 12AT7). I replaced them with regular JJ's and softened things up quite a bit, and later with JJ long plates to get even more breakup at lower volume.

    YMMV based on amp. I like JAN 5751s for low gain, JJ 803s for higher gain. Unless you are desparate I wouldnt change preamp tube type (like a 12AX7 with a 12AT7) as some circuits are made for the values of whatever tube is supposed to be in there.

    A few other things you can do to grit an amp up more- put a clean boost in FX loop to slam a tube power section or hit the front end hard with a boost (guitarists use ODs like TS9 or Maxxon 808 all of the time for this end).
  8. avvie


    Oct 12, 2010
    Maui, HI
    Yeah I'm not asking to get distortion for distortion's sake...I have pedals for that. It did cross my mind that mixing a slightly overdriven tube preamp with a clean SS preamp might be cool. The amp is a Hartke HA7000. Great information you guys are dispensing though!
    Another thing was that thos amp was giving me a bit of trouble (all in another thread) so I was thinking of different ways to approach it and wondered if I should onsider a tube change.
  9. IIRC the "tube" is in the middle of the SS signal chain so you may not notice a lot of difference other than gain loss.