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SVT-III Pro acting funny...

Discussion in 'Amps and Cabs [BG]' started by degroove, May 28, 2004.

  1. degroove


    Jun 5, 2002
    Wilmington, DE
    I was playing an Ampeg SVT III-Pro that i bought off ebay and is about 10 years old.

    When I play, no matter which way I turn the tube gain knob, the tube sound remains the same, and I can not get a clean sound at all.

    I was hoping it might be the preamp tubes. Would they sound fuzzy all the time if they were going, and not get as gainy as possible when cranked?

    This problem exists no matter which way I turn the gain and master. I am using a passive bass, so its not the bass and I do not use any effect pedals.

    Any advice ?
  2. Definately sounds like time for a tube replacement, but Id take the head in and have each of them tested. At 10yrs old it wouldnt hurt to replace them all anyhow.
    Much luck!
  3. degroove


    Jun 5, 2002
    Wilmington, DE
    I am glad you are thinking that its the tubes, cause I am dreading taking it in and hearing its a million dollar repair job!
    I am going to have to find a good amp tech...

    Thanks for your input! :)
  4. cb56


    Jul 2, 2000
    Central Illinois
    go try a new one in a store and see if it's any different. A few years ago we had a discussion about whether the tube gain knob actually did anything! Do a search and you might find that old thread.
  5. victobass


    Nov 27, 2003
    My SVTIII did the same thing and I replaced all the preamp tubes. The original tubes where in for 5+ years when I started noticing the degradation and my tone wouldn't clean up at any volume. That solved the problem! Cost me about $80 for Electro Harmonix tubes.
  6. I had an svt III-pro for about five years and although it was a very reliable amp I found that it was under powered and yes, the tube gain did absolutely nothing. I also owned an svt II-pro and what the tube gain did on that amp was also a mystery to me.
  7. degroove


    Jun 5, 2002
    Wilmington, DE

    Just ordered them (EH) from the tube store. They will be here in a few days. I just saved a lot of money...they have them for $15.00/tube for Groove Tubes at the local store and I don't know how reliable those are.

    Thanks for all of your help!
  8. main_sale


    Apr 26, 2004
    Cape Cod
    Groove Tubes recently released a 12AX7M (Mullard) that is getting rave reviews. Don't skimp on your tubes. You will pay for it with a loss of tone.
  9. degroove


    Jun 5, 2002
    Wilmington, DE
    No worries! I read the reviews on the Tube Store for these tubes is very good. Low microphics and crisp musical detail. THe review states:


    I don't feel like I am skimping. :)
  10. notanaggie

    notanaggie Guest

    Sep 30, 2003
    That control is a voltage control on the tube that drives the output mosfets. If it doesn't make a difference, than either there is an electronic problem or the tube is weak.

    It should vary the available output power and thus the loudness, as far as I know.
  11. main_sale


    Apr 26, 2004
    Cape Cod
    Let us know how the new tubes do. Also, the TUBE GAIN control governs the voltage supplied to the tubes. At 10 the voltage is at maximum and provides a "Dynamic, highly responsive tone." Lower voltages thicken and compress the tone, also can be distorted depending on the volume level. This is generally a subtle effect, but increases as the amp is driven.
  12. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Yep, its a voltage control. Depending on various factors including how loud you play, it may be subtle or obvious.

    I think that control is one big reason people say the 3-PRO has low power. When the power amp driver voltage is low, output is also lower at a given amount of distortion. And of course, with a weak tube, you may not get to full output.

    In any case, you need to be cranked up and using full power to have the maximum effect, because it is a power amp control. At low volume it simply won't appear.