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Impact of changing tubes in a Ampeg SVT4 Pro

Discussion in 'Amps and Cabs [BG]' started by baxter_x, Dec 23, 2013.

  1. baxter_x


    Nov 27, 2013

    I was just wondering if some of you tried to swap the stock tubes of the SVT4 Pro to some other brands.
    I'm not willing to do so, it's just by curiosity that I'm asking.
    For example can you get close to a Mesa M-Pulse head tone by placing Mesas 12AX7 inside the SVT4 Pro?

    If you guys have tried this with other heads, I'd be also pleased oto have your feedbacks ;)

  2. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I don't know who makes Mesa's tubes, but they're simply rebranded new tubes that other companies make with their own brands on them and sell for cheaper.

    In my Heritage SVT-CL, I tried several different tubes in V1...new JJ, a new Ruby, some NOS Japanese Raytheons, a no-name NOS tube, and one other NOS tube (think it was a GE but I can't remember now). They fell into two categories, and the differences occurred only in the NOS tubes. The NOS tubes were ever so slightly brighter and tighter. I ended up going back to the stock JJ because even though it was very subtle, I didn't dig it as much as the JJ. It didn't turn the SVT into a Mesa-sounding bright/tight thing, but it was a little more in that direction.

    You won't be able to turn your 4 Pro into an M-Pulse by changing tubes over to NOS (and IMHO why would you want to?), but you can change its sound ever so slightly by trying different tubes in V1. Unfortunately NOS 12ax7's are outrageously priced now, so I'm done with them, but if you can find a deal on some, might be fun to try. Just don't expect miracles.
  3. baxter_x


    Nov 27, 2013
    Thanx for this very complete answer.
    I'm am not AT ALL trying to turn my SVT4 into a M-Pulse. I just gave that example as, according to me, Ampeg and Mesa are very diferent types of tones.
    I was asking as I've heard many things about changing tubes in an amp.
    Some say it doesn't change much, others say it' really diferent.

    So one day I'll byu a hole set of new tubes from a complete other brand and will give a try.

    But why trying tubes in V1?
  4. To get to the heart of the question, no, rolling your pre tubes will not get you the sound of a different amp. Tubes are a part of the circuit, but not the only part, not even necessarily the most important, amp-depending.

    What you *can* do sometimes is vary the intensity and character of the drive you're getting by trying different brands and types of tubes. But again, it depends on your amp; some are designed to be very responsive to these changes, some will change little. I use a Streamliner with a 3-tube preamp, and I would call the effect of tube rolling significant, in my case.

    JimmyM mentions V1 specifically because that's often where you'll see the most change (that and the phase inverter, in an all-tube amp). A common mod is to replace the 12ax7 with a 5751 to lower the gain a little and give you more of a range to use. I've done before in my Streamliner but have come to prefer a long plate 12ax7.
  5. baxter_x


    Nov 27, 2013
    Great to knwo all that!
    Well, the conclusion is probably very simpel: I just have to try ;)
  6. FWIW Changing the pre amp tube is a really simple swap over and can make a nice subtle difference to your tone. I noticed a definite overall improvement in tone when I changed the preamp tubes in my 3pro.
  7. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Because it's been my experience that tubes in other positions besides V1 doesn't do anything to change the sound.
  8. baxter_x


    Nov 27, 2013
    I know, it's very simple. You don't have bias like a power tube.
    Which tube did you swap for?

    Then do you the purpose of the other tubes? I've always wondered.
  9. B-string

    B-string Supporting Member

    V1 has the "toughest" job, it needs to take the very small signal (from the instrument) and amplify everything, every nuance good or bad to a level the other circuits can use. The job the other small tubes have depends on how the circuit is designed. Generally they take a portion of that signal from V1: bass, mids, treble and shape that portion. Finally the driver tube is a lower voltage gain stage that provides the final level of voltage and or current needed for the "power amp". PI tubes (Phase Inverters) have the job of "separating" the positive voltage swings from the negative voltage swings so those can be used by the "push" and "pull" sides of the final amplifier sections. PI sections are not used in all designs, only when the final amplifier design needs them.
  10. baxter_x


    Nov 27, 2013
  11. JOE EDO

    JOE EDO Supporting Member

    Aug 28, 2007
    Central New York
    Going for lower gain tubes like a 5751 in place of a 12AX7 can make the most dramatic difference in V1...in that the gain structure of the amp will be effected mostly. That may get you some different tones that may work for you. I found that a 12AT7 in V1 in my SVT-VR was a exactly what I was looking for.