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Could my pre amp tube be out?

Discussion in 'Amps and Cabs [BG]' started by triggervision, Apr 7, 2009.

  1. triggervision


    May 24, 2006
    My rig is an Ashdown abm evo 3 with the abm 8x10 cab. I've started to notice a slight distortion sound from my rig...it's a 500 watt head and the cab is 1000 watts. Don't believe it's a blown speaker. Could this be the pre amp tube is in need of replacing? Any help would be appreciated.
  2. bongomania

    bongomania Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Most likely culprit is actually dirt or corrosion on any one or more of the in/output jacks, including the fx loop. Clean all of the jacks with a good cleaner like Caig's, and work some into the pots while you're at it. 99% of the time that solves "mystery distortion".
  3. More than likely not... Have you tried turning the gain down at all?

    Can you provide more information?
    How often? when? what are you doing when it happens?...
  4. pbass62

    pbass62 Supporting Member

    Sep 24, 2007
    Iron Station NC
    if you have any type of effects pedal that will drive a set of headphones,

    come out of amp send to effects input, plug in headphones and make sure your effects is in a dry/bypass mode

    set your ashdown preamp to normal setting and listen for any distortion. If it is still there you have isolated to preamp stage, than check dirty jack, loose tube in socket etc

    If all is well you have either a problem in the pwr amp section or cab
  5. triggervision


    May 24, 2006
    It does it all of the time. I just noticed it about 5 days ago though. Yes, it still does it with the gain turned off.
  6. triggervision


    May 24, 2006
    I'll check that out tomorrow pbass.
  7. triggervision


    May 24, 2006
    bongo I can't seem to find this cleaner you speak of. Maybe I'm searching horribly...lol
  8. bongomania

    bongomania Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
  9. bassman314

    bassman314 I seem to be a verb, an evolutionary process...

    Mar 13, 2005
    Bay Area, CA
    go to Radio Shack or any other electronics hobby store.
  10. marob


    Apr 18, 2005
    Wisconsin, USA
  11. hrgiger


    Jan 11, 2009
    Otherwise go to Home Depot and get a can of CRC QD Electronic Cleaner, best price for a big can, works great for me. Should look something like this:

  12. triggervision


    May 24, 2006
    Could i spray this in the input of my bass? I've put my Thumb and my Stingray through my practice amp here at home and the Thumb still does it...the Stingray doesn't seem to. Will know more about my main rig tonight at rehearsal.
  13. are you playing the same bass through it all the time? Is it active? could be the battery going flat.

    Gives me distortion every time the batteries on its way out...
  14. triggervision


    May 24, 2006
    That will be next...lol..gotta love troubleshooting.
  15. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    Yep. The battery would be the first thing I would check. IMO the preamp tube would be about 10th on the list of things to run down. Best of luck finding it! If you figure it out, let us know. Maybe you can save someone else some heartache down the line.
  16. RedLeg

    RedLeg Supporting Member

    Jan 24, 2009
    Kaiserslautern, Germany
    Nov Shmoz Ka Pop?
    12AX7's last for freakin ever. theyre not like power or rectifier tubes
  17. triggervision


    May 24, 2006
    Changed battery and it quit doing it through my practice amp. Rehearsal is at 7 tonight so I'll post an update then. I think that solved it though *fingers crossed*.
  18. bassman314

    bassman314 I seem to be a verb, an evolutionary process...

    Mar 13, 2005
    Bay Area, CA
    I am going to revive this thread, as I am running into a similar issue with my Ampeg SVT 3-Pro.

    I've attempted the following:
    1) Used contact cleaner in all ports and pots.
    2) Changed speaker cables
    3) had by Aggie Cab checked

    I know it's not the pre-amp section, as I send the pre-amp signal to FOH via a DI and the signal the FOH has is clean.

    I am thinking it *might* be either the 12AX7 used to add dirt to the power amp signal, or the 12AU7 used as a phase splitter for the power section.

    Before I replace the tubes, are there any other thoughts?
  19. MAF sensor? yay!
  20. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Take it into a tech and let him bias the MOSFETs. 3 Pro MOSFETs will sometimes drift. It's a very easy fix, but it must be done by a tech using an oscilloscope, otherwise you can burn the amp up.

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