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Need help for DB750: Tube positions

Discussion in 'Amps and Cabs [BG]' started by mrbassman_de, Nov 1, 2005.

  1. mrbassman_de

    mrbassman_de Supporting Member

    Sep 14, 2003

    Does anybody know which brand of tubes are originally used for the DB750 preamp and in which position (V1, V2, V3, or V4) ?

    The background: Recently I shot a used DB750 on ebay. The enormous power impressed me from beginning, but the tone from the eq seemed to be too brittle, harsh, quite uncool - compared to others. As far as I don't use equalisation very often I left that as it is.

    But today I checked the tubes and found 2 CHINA 12AU7 in position V2 and V3 !! In position V1 I found a Sovtek 12AX7WA, in position 4 a Philips JAN 5814A (=12AU7). I think the Chinas must be replacements by a lazy "technician" ? I expected 3 12AX7s and only 1 12AU7.... so the Chinas should be 12AX7s, right ?

    Does anybody know whether a preamp could be damaged by such a wrong replacement ? And what are the differences of 12AU7s and 12AX7s ?

    Last question: Anybody out there who checked out NOS tubes like Telefunken, Mullard or Tesla (no JJ) for the V1-3 positions ? Any advise would be helpful ....

    By the way - the Sovtek V1 was microphonic at purchase date. I don't like Sovteks....

    Thanks and best regards from Germany
  2. mrbassman_de

    mrbassman_de Supporting Member

    Sep 14, 2003
    No one who knows the original brand of tubes ???? Aren't they labeled ??

    But the position: C'm'on, guys ! I remember some posts where some of you told us that you checked out tube replacements in the DB750. You should know at minimum where the one 12AU7 tube is located instead of the 3 12AX7 tubes...
  3. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL

    i dont think the Aggie guys use anything NOS if that's what you're hinting at.

    FWIW, i'm pretty sure they just use whatever EH tubes they can get their hands on. nothing too fancy.

    btw, check the website, and there should be a FAQ of some sort, there.
  4. kringle77

    kringle77 Supporting Member

    Jul 30, 2004
    Massena NY
    The phillips may be origional and I think they use sovtechs or similar. I personally think that Tesla tubes are very clear but sort of brittle. For me, it's Ei gold tubes all the way for 12ax7's and Jan/Phillips for AU7's. Warm, clear and tight.
  5. Aguilar/Dave B.

    Aguilar/Dave B. Aguilar Amplification Commercial User

    Nov 8, 2003
    New York City
    President: Aguilar Amplification
    Tube quality is always such an issue. Remember that most premium tubes you buy are the same as the cheaper tubes except that half the batch has been tossed!
    In the old days (that would be the 1990's) we could get really nice NOS preamp tubes for a reasonable price. We use to use a lot of JAN Spec 12AX7 and 12 AU7's. I think the JAN spec codes were 5751 and 5814.
    We got GE's and Phillips and Sylvania's.
    By 2000 or so the availability of good NOS tubes at a reasonable price was pretty much shot, at least as far as our sources. We like the 12AX7's from Sovtek, we get some Sovtek (New Sensor) 12 AU7's and some chinese 12 AU7's. It would be great if Mullards could be had! But no.....!The DB 750 never had NOS tubes in it, though. Some of the early DB 680 might have had them.

    The tube layout for the DB 750 is: Three 12AX7's across the front of unit.
    The tube on the "dog leg" of the preamp board closest to the back of the unit should be a 12AU7.

  6. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL
    if anything, i dig the fact that the amp's tone isnt hinged to a $200 preamp tube.

    sure, a nice mullard will sound nice in my aggie 680, but being able to use my backup EH's and yet not have any adverse reaction to the amp's tone is a very cool thing. :cool:
  7. mrbassman_de

    mrbassman_de Supporting Member

    Sep 14, 2003
    Thanks for your interesting posts so far !

    @dave: I heard about the JAN tubes with the spec 5751 have a little bit less power than the modern Sovtek tubes. Did Aguilar change also the electronics when changing the brand of tubes ?