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Tubes in svt3 pro

Discussion in 'Amps and Cabs [BG]' started by sleazylenny, May 9, 2003.

  1. sleazylenny


    Jun 20, 2002
    Mpls, MN
    Hope you can help me.

    I posted awhile ago about some problems I had with my sound decreasing or dropping out completely. Deductive reasoning boiled it down to my amp or my guitar. So I 'm taking action with both. My question lies in the amp part of the equation.

    On advice of a friend I'm putting in new preamp tubes. I bought 3 12ax7's, opened up the amp, SURPRISE!!!!! There are 5 tubes total.

    Back to Talkbass. Research. Ahhhh, the other two ( 12ax7 and 12au7)are driving the mosfet power section. ok. So here's the question. The tubes driving the power section are burning pretty bright. The ones in the preamp not so bright. replaced preamp tubes and they burned less brightly. Swapped this and that, Tried a new 12ax7 in the driver section, it also burned less bright. So when a tube burns bright, is that an indication of a problem? Would a drop out of sound be more likely from preamp tubes or driver tubes? Should I replace all of them? Is there anything I'm forgetting that's gonna make my amp blow up tommorow night in the middle of a gig? Any advice would be welcomed.

    ( btw, I did a search, tons of them. couldn't find any thing direcctly related to these questions)
  2. Bump for you Lenny,

    as an owner of a SVT-3 Pro I'd like to know more about this issue myself. I only have this amp for two months now and I'm very happy with it.

    What's the influence of different types of tubes on the sound of the amp?
  3. sleazylenny


    Jun 20, 2002
    Mpls, MN
    Boy, that's a subject of huge debate. Some poeple here seem to be on a never ending quest for the holy grail of preamp tubes. Others say they matter not, tube sound comes from power tubes, not preamp tubes.

    Me personally, I don't care much. I just want my amp to function. I got a good deal on some boogie tubes and replaced my preamp section. Later today I'll get the tubes for the driver section. But still my question remains.

    Why were my driver tubes burning more brightly than my preamp tubes? Is this normal? I imagine there might be more juice running through them. Or is that the sign of a bad tube?
  4. I don't know about burning brighter but drive tubes definately run hotter than they would in the preamp section (about twice as hot in my vintage svt). So I would say that this is normal and not to worry about it too much.
  5. The "brightness" of tubes has NOTHING to do with their sound or performance. All you are doing is seeing an exposed heater coil. The only difference from an exposed heater is that of manufacturers' design. It makes NO difference in sound whatsoever!

    The problems with the SVT3Pro are WELL documented here and have NOTHING to do with the tubes anyway. I'm very surprised you didn't see anything about them when you researched the amp. I had one and got rid of it because it was an unstable amp.Three times rebuilding it was enough for me. It also would drop volume out of nowhere. The problem is with the power supply rails and their associated relays and unfortunatley, once they get outta whack, the amp will suffer from a cascade effect and you can expect a whole bunch more to go wrong with it.

    BTW, it is an outright LIE on SLM's part to say that the amp has "driver" tubes. If you'd like, I'll give you the number for the driver transistors that push the power section. It's nothing a but a REALLY crappy solid state amp with a noisy tube preamp.
  6. :p Well yeah, but I happen to like mine :)
    I only have it for two months and I'll see what the future brings...

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