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Aguilar DB750 problems

Discussion in 'Amps and Cabs [BG]' started by mbjensen, Mar 29, 2009.


  1. mbjensen

    mbjensen

    Aug 11, 2008
    I have just purchased a used Aguliar DB750 and was out playing a job last Friday without any problems. then yesterday, after playing with my band for a few hours the cabinet starts to make a loud noise as if the units was blown. I tryed to connect the amp to another amp and the same problem again. It's like the amp can't handle the vibration from the cabinet because when the amp stands beside the cabinet, instead of on the top, there is no problem.
    Do anybody know what the problem can be??
     
  2. jmac

    jmac

    May 23, 2007
    Horsham, Pa
    Just a guess, but it might be a tube issue. Either loose or bad.
     
  3. silky smoove

    silky smoove

    May 19, 2004
    Seattle, WA
    Open up the amp and see if any of the tubes are loose.
     
  4. mbjensen

    mbjensen

    Aug 11, 2008
    I have just open up the amp and none of the tubes seemed sitting loose. But will try the amp again tomorrow.
     
  5. ttyR2

    ttyR2

    Feb 23, 2003
    Athena, OR
    You can easily check for microphonic tubes by *gently* tapping them with a chopstick while the amp is on and hooked to a speaker. Any tube that generates sound when tapped is due for replacement.
     
  6. Yes to any wooden light stick, no metal and plastic does not work as well. I've always used an "orange stick" like for fingernails.
     
  7. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    rather than a tube, it actually sounds like a "cold' solder connection or a loose component (not fully soldered) to me. and you can use the chopstick method to find it as well.

    it could also be the send/receive jack's switches. if so, try a 1/4" to 1/4" cable from the send to receive and see if that solves it.

    2 cents.............
     
  8. mbjensen

    mbjensen

    Aug 11, 2008
    I tryed to check for microphonic tubes and there was no sound with any of the 12AX7 tubes but the 12AU7 tube made a little high sound and the cabinet began to make more noise also with out tapping the tube but just holding the pen close to it. Do that means it have to be replaced? Found out that you were right johnk_10 the sound i had heard yesterday came from a component when i was tapping it. The component and the 12AU7 tube was placed close together so are not sure the sound in the cabinet came from the 12AU7 tube but it still made a little high sound when beeing tapped.
    Would you adwise my to try to fix the componet my self or do i have to find a store where they can fix it?

    Thanks for the help so far!!
     
  9. silky smoove

    silky smoove

    May 19, 2004
    Seattle, WA
    Trying replacing the 12AU7. Its cheap and easy.
     
  10. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    i have found 12AU7's to be alitte noiser than 12AX7's. if the chopstick test makes a difference on a component, its probably a capacitor that is not soldered too well. i don't know what type of soldering experience that you have so its hard to say whether you should try and repair it yourself, but it really isn't very difficult to add a little solder to a bad connection. you just have to be VERY careful not to overheat the traces (or it will lift) and it should be fine.
     
  11. Ryan L.

    Ryan L. Moderator Staff Member Supporting Member

    Aug 7, 2000
    West Fargo, ND
    Did you ever figure out what the problem was??

    When using mine last weekend, I had a little bit of crackling going on once in awhile.
     
  12. geoffbassist

    geoffbassist UK Double Bassist Supporting Member Commercial User

    Jul 17, 2006
    UK
    Founder - Discover Double Bass
    i had the same problem and just repalced the tube that had gone microphonic...
     
  13. Ryan L.

    Ryan L. Moderator Staff Member Supporting Member

    Aug 7, 2000
    West Fargo, ND
    I'll have to open mine up and see what's going on with it. Hope that's all it ends up being.
     
  14. Ryan L.

    Ryan L. Moderator Staff Member Supporting Member

    Aug 7, 2000
    West Fargo, ND
    Well, I think I got it figured out. I opened it up, and when I tapped on the tubes, the ones in V3 and V4 positions rang out like a bell when I lightly tapped on them.

    BUT, someone has replaced the tubes in mine at some point, and put all 12AX7's in it (ElectroHarmonix Russian-made ones). I've read that there is supposed to be a 12AU7 in it in one of the locations---where is that one supposed to be, and what, if any, negative effect will having a 12AX7 in it's place have on it??

    Bear with me, I'm new to this tube-replacement business.;)
     
  15. 12AX7's are High Mu triodes, 12AU7's are medium Mu trides. The 12AX7 has a lot more gain but IMO, please note to all those "YOUR wrong on this" people on this board, IMO in IME a 12AX7 in place of a 12AU7 sounds harsh and limits the bandwidth. For bass you are {again IMO and IME} better off using the 12AU7 in its designed circuit.
    IMHO :)
     
  16. Ryan L.

    Ryan L. Moderator Staff Member Supporting Member

    Aug 7, 2000
    West Fargo, ND
    Thanks for the info.

    Which spot is the 12AU7 supposed to be in, so I get it right??
     
  17. I don't have the layout for your amp, but as a general rule it will be the furthest tube from your input jacks. The manual maybe avalible online if there is no labeled position inside or outside the amp?
     
  18. Buogon

    Buogon

    Feb 2, 2009
    New Jersey
    I wonder what happened to Oskar Cartaya's DB 750 at the bass bash at JT's in Aneheim
    was anybody else there. I know that it went out on him and i think he replaced it with a 500. I did'nt have time to ask him.
     
  19. I just checked their site and it was no help, but looking at the amp layout I would bet it is the center most (front to back) tube. The three in front being 12AX7's for preamp and EQ.
     
  20. Ryan L.

    Ryan L. Moderator Staff Member Supporting Member

    Aug 7, 2000
    West Fargo, ND
    Yeah, I checked the site too, and found nothing. I'm sure another owner will chime in here at some point.:) But I think, IIRC, you are right. I'll have to do a search here, but I seem to remember someone saying that the V4 spot was where the AU7 tube goes, and that's the one you mentioned.
     

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