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Swapping 12AU7's with 12AX7's

Discussion in 'Amps and Cabs [BG]' started by Rockit, May 2, 2006.

  1. I suppose this might be best answered by the Ampeg guy but here's my question. I have an SVT-CL that I love but it's just too clean sometimes and I want to overdrive it. I've read about gain factor for different preamp tubes on a few sites and basically, 12AX7's are the hottest out there. I've also read that you can swap out 12AU7's with 12AX7's but I'd obviously rather know up front that I'd be risking some serious damage to my head that to find out after I've already done it. I'm really into a raunchy, bottom heavy bass sound and have been using a pedal to achieve this sound. Anyone with any experience doing this???
  2. Seeing the 12AU7s in your amp are only in the driver section you will more than likely make a mess and get nothing but total ott distorted crapped out sound

    Talk to bob over at eurotubes and get some of the higher gain 12AX7's in the preamp section, that should help a bit

    - Will

    (or get an overdrive pedal)
  3. Turn the gain knob UP, boost the mids, keep the ultra low OFF. The mid knob and ultra low do make a huge difference. It'll distort a lot more like that.

    12AX-7's are the hottest pre-tube type you can put in there. 12AU-7, 12AT-7, ect. would only lower the gain. Though like the above poster said, they're in the PI circuit, not the actual pre-amp.

  4. Daytona955i


    Feb 17, 2005
    Albany, NY
    SVT-CL can get nasty dirty and sound awesome, what bass are you playing?

    +1 on cranking the gain up.
  5. Basss -
    Epi LP Bass
    Epi TBird
    Fender Jazz
    The Jazz has alot of growl, the 2 Epis are fat with lot's of bottom

    Gain - is on 6/6.5, I can't go beyond 2-1/2 on the Master without my band complaining. I use an MXR M80 for the overdrive. I've read the older SVT's can really overdrive but my experience with my CL is loud and clean.
  6. Your problem is you arent going loud enough :p

    Newer SVT's can growl, just not as well as the older ones! (and to put something in place, the older SVTs didnt have a pregain, so if you wanted to get the best growl, you gotta crank and get those power tubes going!)

    Try turning the gain up a little bit more and the master down a tad, if you arent able to go loud you wont get the power tubes going (which is where the best sound is!)

    And like has already been said, crank the mids!
  7. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    12au7's are clear, clean and way low gain. I tried one in my F2B and for bass ... it sucked. I just got a gucci Chinese grey plate 12ax7 from Lord Valve. I'll be loading it up Friday and doing a comparo against a Mullard, a Reflektor Tung SOl clone and a JJ ECC83s (I think it's an 83S , might be an 82s ... Friday I'll check)
  8. I experimented with putting 12At7 and 12au7's in my boogie. Sometimes I could get a good growl by folowing a 12ax7 with a 12au7. But I also lost a lot of bass response. I second what teh other guy said. Get higher gain 12ax7s. Heck they are cheap and easy to come by. Get several. It can be difficult to tell the difference that one tube in a multi tube setup makes.
  9. 12AX7 = ECC83S
    12AU7 = ECC82

    They are the same tubes, thats just the different branding (12ax7 etc is the US branding, ECC83S etc is the UK/Europe branding IIRC)

    [This isnt like with 6550's and KT-88's which altho are interchangeable they are different tubes]

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