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Help - Tube Amp Question

Discussion in 'Amps and Cabs [BG]' started by larry, Oct 13, 2004.

  1. larry


    Apr 11, 2004
    I'm kind of embarassed to ask this. I've been playing for 20+ years, but I'm just not a gear-head.

    How do you know when the tube in your amp needs to be replaced? I have a SWR SM900 that was working fine, now when I power it up it's really noisy and distorted for about 15 minutes, then seems to work ok when it's warm. Is the tube the issue, or something else? I don't like my local service center, I don't want to bring it in unless I have to.

  2. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks
    You should change tubes once they are broken, or sound bad. It's the same way you know when to change strings, really.

    Since it's just a preamp tube you're talking about, you should go buy a couple more and try swapping them out in your amp, and see the tonal difference. A preamp tube should cost you about $8.
  3. A preamp tube should last longer than YOU, especially one in most so-called "hybrid (which they're not, but I digress)" amps. That said, SWR has not always used the best tubes and it IS entirely possible the one in your amp has somehow had a manufacturing defect manifest itself. If you've not noticed anything before, I doubt you have a tube problem, but it is cheap and easy to swap a preamp tube. Your problem sounds more like something else related to the output section or power supply though.

    No it isn't. Is Mesa trying to sell more tubes? Barring defect or malfunction, most players will NEVER "wear out" a preamp tube. I have yet to hear of anybody "wearing out" a preamp IC and they both do EXACTLY the same thing nearly the same way.
  4. Frank Martin

    Frank Martin Bitten by the luthiery bug...

    Oct 8, 2001
    Budapest, Hungary, EU
    Sounds more like a bad solder to me...
    Bad tubes make other kind of noises - like microphonics - AFAIK