12AX7 preamp tube differences?

Discussion in 'Amps and Cabs [BG]' started by abarson, Jun 20, 2008.

  1. abarson


    Nov 6, 2003
    Santa Cruz
    I recall seeing on a different forum a comparison test of different 12AX7 tubes in a guitar preamp, and was wondering if anyone had done such a shootout for a hybrid bass amp? Tube selection is supposed to have a lot of influence on clarity, harmonics, etc.

    I'm also curious about whether the 12AX7 can be replaced with a 12AU7, and what the expected change would do?
  2. Simon Langley

    Simon Langley

    Jun 19, 2007
    Chico, CA
    This is something I am also curious about, subscribed.
  3. Steve


    Aug 10, 2001
    I think....the AU will have a lower gain. I'm sure a guru will show up soon.

    Yeah, you can hear a difference. IF your rig has enough resolution. Most don't. A lot of cabs are scooped around the frequencies where you would hear a difference.

    Put something SWR on top of an Acme cab and you can definatly hear it.

  4. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    In 30 years of playing, I've never noticed a sound difference in brands of 12AX7's in my amps. But I have noticed a difference in build quality. I tend to stick with NOS on preamp tubes because of that, but if I can't get them, I try to stick with Russian brands.
  5. bongomania

    bongomania Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    A key issue:
    Some tube preamps are designed in a way where different tubes will have a strong impact on the tone, while others are more subtle, and yet others are designed in a way where there will be no audible difference between tubes. So you can hear a difference between preamp tubes, but only in certain preamps- and a lot of the time the differences will be very subtle.

    There have been a number of bass-amp-specific tube shootouts and "name-your-favorite-tubes" threads here; searching for them may be tricky because the threads I'm thinking of are old, but if you search on certain popular vintage tube brands such as Mullard, Telefunken, Brimar, Tung-Sol, or Amperex you may find a trove of information and opinions.
  6. I've noticed a distinct difference in both the Sovtek 12AX7WA that came stock in my Hartke 3500 and the JJ ECC83s that I swapped it with.

    As I mentioned in another thread regarding the tube pre on the Hartke, to my ears

    Sovtek 12AX7WA: strong bass, louder, but harsher tone.
    JJ ECC83s: weaker bass, softer, but smoother tone.

    I eventually chosen the JJ ECC83s and compensated for the weaker bass using EQ and softer volume by turning up the volume knob.
  7. lavmonga


    Jul 27, 2007
    New York, NY
    I've also noticed different tones and volume levels when changing 12ax7's in my Mesa MPulse600. I had the original Russian Mesa tubes in and swapped them out for Sovteks. It's strange but I had the complete opposite reaction in my amp than Marill had above. The Sovteks put out a weaker output, the clarity was there, but instead of getting the volume I wanted at 3 or 4on the dial, I had to juice it up a bit more. I switched back to Mesa Russians (which are terribly overpriced) but I got my sound back loud and clear.
  8. then i guess if you ever tried the JJ you may find them even softer...