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Ampeg SVT Vacuum Tube Injection DI

Discussion in 'Amps [BG]' started by bassfart, May 7, 2012.

  1. bassfart

    bassfart Gold Supporting Member

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    Hey, I just bought one of these baby's from a fellow TBer and I was wondering if I changed the preamp tube from a G12AU7 to a 12AX7, would that make a drastic change in the sound that this unit produces?
  2. BogeyBass

    BogeyBass

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    probably not, other than depending on age and quality of the current tube. You could get overall improvement by just using a new higher quality tube.

    the 12ax7 could add more gain most likely not needed.

    12AU7 is med mu tube probably chosen for a lower output impedance and ability to provide more current to drive the DI isolation transformer. 12AX7 could raise the impedance and reduce its ability to do this. not really by much depends on Ampegs design which appears to be a cathode follower.

    so you would look for the lowest output impedance
    typical values as cathode follower for 12AU7 is 400/500ohms
    12AX7 600/700ohms 12AT7 200/300 ohms.

    So maybe try 12AT7 think it is considered a high mu tube, not as much as AX7 but will increase gain and keep the impedance low. Or just use a new high quality tube as specified by manufacture
  3. DJJazzV

    DJJazzV Spaulding get your foot off the boat! Supporting Member

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    Possibly, but it would increase the output quite a bit. That may make it too hot a signal for the board. It was built for a 12AU7.
    What are you trying to achieve in tone?
    My favorite tube in it is a Telefunken ECC82. That is very detailed low, mid, and high. 2nd favorite is a JJ Gold Pin 12AU7. Very detailed, but not as full in the low as the Telefunken. Enjoy the great DI box. It also works well to add the tube signal to the Thru (Line Out) to feed a small class D amp.
  4. T-Bird

    T-Bird

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    Hi.

    I haven't done any tube rollin' with mine, but I'll go with the "probably not" answer.

    Mr. Tiers may be able to shed some light on the designing goals on that unit, but generally any mass produced tube equipment today is designed to be rather insensitive to tube changes. Makes the life of a manufacturer a lot easier in the long run.

    I'd guess that if You need to drive a power amp straight from the SVTDI, using a higher MU tube might be beneficial. IME the gain is hot enough as-is for any mixing desk or other equipment one may wish to connect the SVTDI to.

    Regards
    Sam
  5. Jerrold Tiers

    Jerrold Tiers

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    The impedances in the unit are such that probably no HUGE change would occur, but the available headroom might change.

    Since both tube types are possibly the most available types in the world, why bother changing?
  6. jplumansoc

    jplumansoc

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    the DI comes with a 12ax7 from groovetube. not a bad tube imo. i've also tried a Svetlana and sovtek 12ax7. I can't remember what models but I was a big fan of the sovtek, really brought out the mids to make it a bit punchier and warmer.
  7. Mendouza

    Mendouza

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    Hi, i´m reviving this particular comment as i can´t find information about this Ampeg SVT DI BOX. i recently aquired it and would like to know if somwone knows if i could use this Ampeg SVT DI Box with 220v as i´m in South America? It´s not clear on the box, it only indicates Fuse T. 5A/125v - T. 25A/250v. Do i only have to replace the fuse or use a 125 v transformer?
    Thanxs.
  8. T-Bird

    T-Bird

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    Hi, Mendouza.

    My unit (SN D5DWQ30018) has the "W-Export 230 Volt" sticker above the IEC socket, as well as "Line 230V ~ 50Hz Pwr:30VA" in the identification sticker on the bottom of the unit.

    If Yours is missing both, the PT in mine is "SLME 94-251-40".



    Regards
    Sam
  9. Jerrold Tiers

    Jerrold Tiers

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    If the transformer is a "94-XXX-40" as I believe most or all are for the DI, then it can be re-wired for either 120 or 240 (nominal).

    The DI snuck out while I was busy with other stuff, and I don't have a lot of inside info on it. The designer of it is Obeid Khan.
  10. bass.player

    bass.player

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    I wished Ampeg would put the SVT Vacuum Tube Injection DI back in production..:hyper:
  11. garmenteros

    garmenteros Junkyard Scout Gold Supporting Member

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    I want one, I own a radial JDI and am very happy with it but wouldn't mind having the ampeg around and leaving the JDI as a backup even though I feed the JDI my ebs tube preamp.
  12. Mendouza

    Mendouza

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    Hi, thanks for the heads up. i contacted Obeid Khan and he replied immediately with great response.
    He said to use a step down transformer with the ampeg SVT DI as it is to use it in 220v environments and he confirmed that it can be easily rewired for either 120 or 240v. "For the fuse value you could leave the same and it would not hurt anything and still give you the protection you will need."
    Doing this research i found his audio products under Khan Audio Products where he is offering a new DI box VTDI as a all tube direct box, and as being the designer of the original Ampeg SVT DI i wouldn´t hestitate on getting this new version as he describes it as a faithful re-creation of the classic Ampeg SVTDI if i were looking for one.
    http://www.khanaudio.com/products/16/Vacuum-Tube-Direct-Injection/
  13. kirkm24

    kirkm24 Supporting Member

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    Has anyone bought from this guy? I'm a little apprehensive spending that kind of money from a relatively unknown source, even by boutique standards.
  14. JimmyM

    JimmyM Supporting Member

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    Disclosures:
    Endorsing: Ampeg Amps, EMG Pickups
    I never bought from him, but Obeid Khan was a longtime engineer for SLM/Ampeg and co-designed the B-15R with Jess Oliver, so it's not like he's a fly-by-nighter.
  15. Floyd Eye

    Floyd Eye

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    He is also now the in house tech at Killer Vintage. Where I may ( or may not) be taking my CL for regular check-ups. Dude is a legend here.

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