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70's SVT Preamp Circuit Update *Need Help Quick*

Discussion in 'Amps and Cabs [BG]' started by GC4, Apr 21, 2009.


  1. GC4

    GC4

    Apr 6, 2008
    Toronto, Ontario
    Hey guys,
    I have my 70's SVT in to my tech right now getting the caps replaced and he was asking if I wanted him to update the preamp circuit so it would run on 12AX7's vs. hard to find 12DW7's I think it is. I'm wondering if I should have him do this or if it will change the sound?

    I just need a reasonable answer quick because he is leaving for a week so needs to get it done ASAP.

    Thanks for the help.
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    IIRC 12AX7's are higher-gain than 12AW7's; if that's correct, and if you don't want more gain in the preamp stage, then you might instead have him adapt it for lower-gain tubes like 12AU7 or 12AT7, which are common enough.
     
  3. GC4

    GC4

    Apr 6, 2008
    Toronto, Ontario
    Sorry, I ment 12DW7's. There was an ampeg circuit update for this I believe at some point. I just don't know if it will change the sound.
     
  4. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    It shouldn't change the sound since 12DW7's are merely half 12AX7, half 12AU7, but your tech is wrong about availability of 12DW7's. Not only are 12DW7's widely available as NOS, they're still being made. I don't know all the companies that make them, but at least JJ makes them. I would never change the tubes in a 70's SVT to the updated circuit. Never never never.
     
  5. GC4

    GC4

    Apr 6, 2008
    Toronto, Ontario
    Thanks Jimmy, I wasn't feeling the idea but I wanted some input from you guys. I also just came upon a thread talking about it, http://www.talkbass.com/forum/showthread.php?t=121104, so I'm going to not go with that update.

    Thanks for the quick replies guys.

    George
     
  6. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Just for your information: The 12DW7/ECC832 is in current production by JJ. Antique Electronics have them for $10.95 or $22 with gold pins.

    Paul
     
  7. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I just went looking for other current manufacturers of 12DW7's besides JJ, and it looks like Electro Harmonix makes one, and Ei's listed as making one, but it's either out of stock everywhere or it's no longer made. The EHX's are double the price of the JJ's.
     
  8. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
  9. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    John, that site iS Antique Electronics.

    Paul
     

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