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Tubes for SVP Pro

Discussion in 'Amps and Cabs [BG]' started by TONYTHOMAS1956, Nov 13, 2012.

  1. Ok. I just purchased a 96 Svp Pro and been reading a lot about noise from these pre's so my question is, Which tubes (Brand and position V1 thru V5) is the best compliment for this pre. I have a 3 Pro that I re-tubed with JJ's and I like the the tone of it.
  2. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    I have an older SVT IIP but if you ask me the best sound longest lasting
    with best signal to noise has to be a Mullard CV 4003 in place of the 12au7 and Mullard CV 4004 or Telefunken ECC 803 in place of the 12ax7.
    But then when you look up the NOS prices you will soon realise that I may be not the only valve nut that thinks this is true.:bassist:
  3. Agreed on the NOS's.Thanks for the reply and I forgot to mention that this is running into a Qsc RMX 1450 into 2 410's
  4. ; Stock tubes and functions
    V1 = (12ax7) Initial gain / DI
    V2 = (12ax7) Bass / Treble
    V3 = (12ax7) Midrange
    V4 = (12au7) Drive
    V5 = (12ax7) Master

    ; BGavin 2003/May BBPDP50039 Factory stock tubes
    V1 - Groove Tube GT12AX7C
    V2 - Groove Tube GT12AX7C
    V3 - Groove Tube GT12AX7C
    V4 - ElectroHarmonix 12AU7A/ECC82EH
    V5 - ElectroHarmonix 12AX7E

    ; User Hotrodded tube combinations
    V1 - JJ Tesla ECC83S (12ax7)
    V2 - JJ Tesla ECC83S (12ax7)
    V3 - JJ Tesla ECC83S (12ax7)
    V4 - JJ Tesla ECC82 (12au7)
    V5 - ElectroHarmonix 12au7a/ECC82EH

    ; GMSweet Hotrodded tube combinations
    V1 - Ruby 12AX7AC5 HG+
    V2 - Penta 12AX7
    V3 - Penta 12AX7
    V4 - JAN 6189W (12AU7)
    V5 - Ruby 12AX7AC7 HG

    Link to SVP Schematic Long Thread
  5. Thanks bgavin. That's what I was looking for. I could not see
    Any markings on the tube board that indicated v1,v2 etc,
    Can I assume v1 starts on the left (facing the front of the pre)
    And goes in numerical order to the right?

    Thanks so much for info.
  6. The tubes are numbered V1-V5 from left to right when the unit's control panel is facing you.
  7. ThisBass


    Aug 29, 2012
    Tube stages in numbered order referring to the signal flow are:

    V1b: Initial / Gain
    V1a: Bright and Low Boost

    V2b: Ultra High Boost

    V3b+V3a: Tone Stack Bass/Treble

    V2a: Drive Stage 1 (includes the Drive-Pot). V2a includes Midrange as well (feedback Loop).

    V4a: Drive Stage 2
    V4b: Tone Stack Midrange + Drive

    V5a: Out
    V5b: nc

    DI routing switched to "Pre" means: DI isn't on any tube at all

    The summary is:

    V1: Initial / Gain / Bright + Low Boost

    V2: Ultra High Boost / Drive / Midrange

    V3: Tone Stack Bass/Treble

    V4: Drive / Tone Stack Midrange

    V5: Out

    so it's obviously a very tricky painful work to change some tubes on the svp pro ....
  8. Tuned


    Dec 6, 2007
    Can't go wrong with JJ Tesla, beyond that it gets very expensive and the benefits are marginal. I used to have an all tube hifi stereo amp and two friends had the same model, so we've done extensive tube comparing under audiophile conditions. NOS Telefunkens are fantastic, but the benefits were mostly stereo imaging and high treble clarity, neither of which apply to bass guitar.

    If there's anything to fuss about with different tubes it's the break-up characteristics when they're slammed, which will vary more. But if you're not a tube slammer then don't bother.
  9. Thanks for all the replies.
  10. ThisBass


    Aug 29, 2012
    Some notes to noisy hiss and drive and midrange.

    The Drive consists of two gain stages (similar like the legendary Boogie Drive design or the Hiwatt OL design).
    These two stages are realized by V2a + V4a.
    The summary of both gain stages must come to a recognizable hiss, that is due to the strong amount of gain.

    Even with Drive-Pot at "zero" there is no way to reduce this gain cause it is all the time present.

    May be it is possible to reduce the summary of gain with 12AU7 for V2.
    But I don't know this moment how 12AU7 for V2 impacts the stage for Ultra High Boost and therefore the signal flow to the Tone stack Treble/Bass.
    By the other hand V2 is part of the midrange schematic and 12AU7 for V2 impacts the midrange as well ....

    But IMO it is not possible to reduce hiss/noice with 12AU7 for V5.
    If noise is reduced then the signal level is reduced the same way.

    V5 works as a output buffer stage and should not make significant noise, neither with 12AU7 nor 12AX7.

    I was wondering a bit why the original design is 12AX7 for V5, I'd suggest 12AU7 for buffer stage anyway ...
  11. capcom


    Mar 23, 2005

    I also have this preamp for a while and still discovering it's tonal possibilities every week at stage.

    Thanks for more detailed description of what each tube is responsible of. This also explains my experience so far with this preamp how especially midrange and drive controls change the character of the sound ranging from clean Hi-Fi like sound to 70's growly aggressive mid tones. I indeed realized early that the actual Bass, Midrange, Treble and Drive controls weren't like any other ordinary eq controls.

    I still have original factory tubes also by the way. Mine has also some hiss and hum but not too serious. However I am still thinking about changing all the tubes in the future to see how it will effect overall sound and noise levels. Therefore I would like to thank also Bgavin about his post for tube brands.
  12. Post #109 is a link to my RTA results of various SVP-Pro tone control settings with the factory stock tubes.

    The charts show the various interaction of the tone and drive controls.
    I did not bother with the graphic EQ, since I have no plans on using it.
    I understand it introduces hiss, and can easily drive the circuit into clipping.
  13. ThisBass


    Aug 29, 2012
    Some curios design of the drive I have to note:

    The drive pot interacts most with midrange and (or but?) Tone Stack Bass/Treble as well.
    I don't know how to tell in easy words but, the SVP drive is a very sophisticated but also complex design that is painful to understand/interpret by only schematic drawing.

    There are lot of tube preamp designs out there like Hiwatt and Fender and many others as well that are easy to read. Even the 70s SVT (and SVT-II) preamp is an "easy to read" design in comparison to the SVP.

    All I have to say is:
    Congrats and deep respect to the designers/engineers work.
  14. capcom


    Mar 23, 2005
  15. AnchorHoy


    Dec 29, 2008
    New Jersey
    Thanks for posting this OP

    I'm using a very similar setup to yours (SVP Pro > PLX 1804) and always wondered if I could improve on the already good results by swapping out stock tubes in the preamp

    bgavin's summary of options is pure gold :cool:
  16. Thanks for the kudos, but I'm just the librarian who collected input from others.
    My thing is speakers, not electronics.
    I can't read a schematic and understand the circuit like my Dad could.
  17. capcom


    Mar 23, 2005
    One of my friends just borrowed me 3 used JJ brand ECC83-S tubes. So I tried them few hours ago at home.

    Initial Condition:
    Unit produced in 2007. I bought it used at May 2012. Had stock tubes in it:
    V1) Groove Tubes GT12AX7R (Sovtek 12AX7WA/7025 Made in Russia)
    V2) (No Name) 12AX7
    V3) (No Name) 12AX7
    V4) Electro Harmonix 12AU7A Made in Russia
    V5) (No Name) 12AX7

    Final Condition:
    I only replaced V1, V2 and V5 for now with 3 x JJ ECC83-S. Again note that JJ's are already used by the way and I don't know how much they had been abused before.
    V1) JJ ECC83-S <--- replaced
    V2) JJ ECC83-S <--- replaced
    V3) (No Name) 12AX7 <--- stock tube
    V4) Electro Harmonix 12AU7A Made in Russia <--- stock tube
    V5) JJ ECC83-S <--- replaced

    I tested at home at a relatively low volume with a signal chain like this:
    Bass -> Ampeg SVP-PRO -> Power Amp -> 1x10 ported cab

    At first I can say that the tone improved. Bass frequencies are more smooth and deep now. And high mids are also a little bit more "singing". Overall the preamp itself is a little bit more "lively" now compared to old stock tubes.
    Can't say the tone improved a huge amount but there is definitely an improvement.

    Altough The 60Hertz hum and overall noise level reduced a huge amount. Also note that when I approach my finger to 5th tube, the noise doesn't increase. With stock tubes in it when I approached my finger to 5th tube, noise was also increasing noticably.

    I will keep experimenting and will hopefully notice you all again.
  18. capcom


    Mar 23, 2005
    After getting good results from the 3 used JJ brand tubes that I borrowed from my friend, I decided to order 5 new JJ tubes from thetubestore.com.

    New tubes arrived today and tested them few hours ago at home practise volume levels.
    I read in internet that in these preamps, the V1 and V4 affects the sound most therefore I ordered 2 of them to be "Gold Pin" models which JJ claims that they are the selected premium grade tubes in their production line.

    So the final configuration is:

    V1) JJ ECC83-S / 12AX7 (Gold Pin)
    V2) JJ ECC83-S / 12AX7
    V3) JJ ECC83-S / 12AX7
    V4) JJ ECC802-S / 12AU7 (Gold Pin)
    V5) JJ ECC83-S / 12AX7

    I can definitely say that the result is better than ever. Tone improved a huge amount. It is smoother, warmer and punchier. High-mids are "singing" as good as ever and also the 60Hz hum is almost gone completely and the hissing noise reduced a huge amount.

    In the end I can highly recommend using new JJ brand tubes in this preamp.

    Next step for me is to try NOS tubes if I can find them in the future. The preamp's sound is quite good now and can't imagine how reasonably better tubes can improve the tone but perhaps the difference will be like smoking a usual tobacco in a bad pipe versus smoking a well aged tobacco in a good pipe. We will see :)

    Altough I have been using an all-tube head for 20 years at home. I have never experimented or bothered with different tubes before since it's hard to find vacuum tubes where I live. So my experience about the sound of different tubes are very limited however I can understand or feel the sound of a good tube sound.

    I will be playing today with my band at our usual tuesday night classical rock bar gig and the new tubes will also be used first time on stage at loud volume. Can't wait :)

    I will keep experimenting and hopefully will inform you all again.