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changing pre amp tubes in SVT3 for more grit?

Discussion in 'Amps and Cabs [BG]' started by fenderthrupeave, Sep 7, 2008.

  1. I am looking for more of a grittier tone out of my SVT3, I like the overall sound I would just like more of a tube overdriven sound and I was wondering if anyone has some suggestions on pre amp tubes that wouldfit what I am looking for. thanks
  2. DanRJBrasil


    Jun 10, 2007
    Good question, I also have a svt pro myself and I always wonder that too.
  3. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    It would be easier to add a drive pedal in front of your amp. I always suggest an EBS Valve Drive, but there's tons of different ones on the market. Swapping your preamp tubes is a crap shoot, unless you seriously know your tubes.
  4. xshawnxearthx


    Aug 23, 2004
    new jersey
    sovtek matched burned in 12ax7's will definitely add some gritt. my 4 pro is dirty with our without my sansamp.
  5. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    You won't find much difference in preamp tubes. There is some, but it all depends:

    - Your definition of "grit";

    - How much grit you want;

    - How hard you slam your input with the bass;

    A lot depends on the instrument and playing style.
  6. xshawnxearthx


    Aug 23, 2004
    new jersey
    yeah if you want more of an overdriven tube sound, besides getting a sans amp or other drive pedals, try turning up the input gain a bit.
  7. DanRJBrasil


    Jun 10, 2007
    I m gas for it , that is a cool pedal is def in my list, but also would be nice to have that grit in the amp ;)
  8. I run a hot signal out of my effects and with my gain about 1 o'clock I get the "clip" light going pretty much constant while playing heavier parts. I am just looking for some of the sort of over drive grit with good low end that I havent been able to find with a pedal.
  9. Red Planet

    Red Planet

    May 29, 2005
    Get some JJ ECC803's and replace the 12ax7's with them. Careful not to replace the 12au7's with a 12ax7.

    The long plate higher gain ECC803 will push the amp more and get you some more grit.
  10. birminghambass

    birminghambass Supporting Member

    Sep 18, 2002
    Birmingham, AL
    Adjust the mosfet bias. Mine was TOO gritty, a tech showed me how to adjust it, turn left for a fuzzier tone right for a cleaner tone.
  11. Red Planet

    Red Planet

    May 29, 2005

    Be very careful you can fry the power section if not done correctly.
  12. fireincairo


    Jul 8, 2008
    It can be a tradeoff with new production tubes, in my opinion. You may need to sample some different makes to find the balance of grit and tone you want with your SVT. In general, 12ax7 tubes have the highest amount of gain available, but they can vary between tubes greatly. Then 12at7 are next in terms of typical gain. There are others, but if you want grit you likely won't find it with any other type of tube.

    The EH 12ax7EH does crunch quicker than some other 12ax7s, but it can be a bit harsh in some circuits. You could go the NOS route and find a nice telefunken or mullard 12ax7, but they can get pricey, though they usually sound quite nice. RFT 12ax7s aren't too expensive, and they are a nice sounding tube, but they can be a bit dark. It may actually be good for a bass amp, come to think of it.

    Also, there are some very decent sounding Mullard 12at7 tubes kicking around the internet for under $20 bucks a piece. For 12at7 tubes, they have a good amount of gain available.

    I just swapped out a stock Peavey 12ax7 for a NOS Sylvania 12at7 in my Peavey butcher and it gave me some more headroom and really smoothed out the tones. I'm pretty pleased, and it's the first tube from my NOS stash I tried. I may try again tomorrow and see what else I can dig up that sounds good, but I'm looking for more headroom from my 120 watt tuber.
  13. fireincairo


    Jul 8, 2008
    Mosfet bias? I thought the SVT was an all tube circuit with a tube power section? Is this a different model he's talking about?

    Anyhow, as far as biasing a tube amp goes, you could pretty much do it by ear if you wanted. Many techs do just that. But, if you want to really zone in to a specific mA so you don't run your power tubes down too quickly, you could get a Weber Biasrite and adjust it. I've done it a bunch of times over the years and it's as easy as can be with a Biasrite with a screen.

    Still, in the end, I usually will tweak the bias pot a little up or down to suit my ear, which is what you really should do because it will yield the best tones. Some amps come alive when you run them hot. Old Marshall amps, for example, really roar when they're run hot. You compromise tube life, but what glorious tones to be had. :bassist::oops:
  14. Too far right, and bye-bye output transistors. It's also worth noting that Ampeg's own service notes on the SVT3 Pro recommend biasing the amp for much less power than its advertised rating in order for the amp to remain stable.

    The SVT 3Pro has a solid state output section.

    Plate current disappation is just a blind guess. If you want to know the amp is actually doing, it requires an oscilliscope and tech know-how.
  15. KPAX

    KPAX Banned

    Mar 22, 2005
    I hate to say it but you might have to get a real svt (all tube 300W). The SVT tone is in the 300W 6x6550 all-tube power amp. I think SLM's decison to call anything but that by the "SVT" name has been a fraud and a mistake.

  16. deaf pea

    deaf pea

    Mar 24, 2005
    Cuernavaca 1 hr S Mexico City
    Seymour Duncan/Basslines SMB-5A Endorsing Artist
    I'm REALLY amazed that NOBODY has mentioned the "tube gain" (IIRC) knob (it's the one next to the "master" volume) . . . full on gives the cleanest sound and anything less WILL sound "grittier" . . .
  17. quickervicar

    quickervicar Supporting Member

    Jul 21, 2006
    Lancaster, PA
    I swapped in a Sovtek 12AX7 in V1 position in search of a grittier tone. I got hotter & fuzzier, but not necessarily grittier. I pulled it.
  18. jimmy rocket

    jimmy rocket

    Jan 24, 2008
    Ayden, NC
    I just sold my 3 pro a few hours ago, but I stumbled upon this thread and thought I'd add a little map of the tubes in a 3 pro that I made:

  19. spode master

    spode master

    Jan 21, 2007
    You have to be kidding me right!?

    That tech was high on Crack telling someone to do that, and probably doesn't know much about what a BIAS circuit in an amp output stage is for.

    I have adjusted my SVT Pro 3 Bias, because I know what I'm doing. I did it on an Isolation Transformer with a AMP Meter, a function generator and an oscilloscope, as well as my ears.

    The purpose is to adjust the bias voltage to get rid of Crossover distortion, not to adjust the amp tone to taste. And it can't limit the AMPS maximum output either. (That would be the Tube Bias or "TUBE DRIVE" Knob At least thats what I read in the AMPEG Manual)

    Just the slightest tweak to far and the output devices will start drawing 2+ Amps of current constantly. That does nothing but generate heat.

    If the Bias is too low you are effectively running a CLASS B amplifier, which is not the most desire able method of running an audio amplifier. The distortion Is not the same as Saturation, and actually becomes less noticeable the louder you are playing. You end up with your note decay having a strange rustly sounding distortion. Not a very pleasant sound to my ears.

    Why not just use a pedal, or overload the pre amp??? Its risky messing with the Bias Circuit if you don't have the proper tools and understanding.

    Seriously who was this tech?? It doesn't sound like he actually has any training as an Electronic Technician.

    My personal opinion is there are better safer ways to grit up your sound than messing with your output stage Bias.

  20. IME Most SVT 3's are actually already loaded with Sovteks.

    Also- that mosfet bias trimpot is SUPER touchy. I've tweaked one by ear once but I wouldn't recommend it to anyone.

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