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400+ making whistling sounds.

Discussion in 'Amps and Cabs [BG]' started by Droog, Apr 22, 2004.


  1. Droog

    Droog

    Aug 14, 2003
    PDX
    So this is kinda wierd. Every now and again my amp makes a high freq whistling like sound. If I pull the bass or treble knobs out and back in again it goes away. For some reason I think its cuz I don't have a rack yet so the amp sits on the cab rattling its poor brains out, basically I think its the pre-tubes getting vibrated kinda loose like. Maybey I am way off base here. Anybody else experiance this?
     
  2. I don't know what's making that high pitched sound, but I suppose it could be from the rattling. Go to a computer store, buy a couple of cheap-o mouse pads and put them under your 400+. This will help with the rattling. Simply putting the head in a rack w/o shock absorbtion won't do much. Save your pennies and get a shock rack. I routinely put a folded up beach towel under my rack on my cabinet during shows. (because I haven't saved enough pennies yet.) Meanwhile, reach behind your amp and make sure all the tubes are seated properly, then take a Phillips head screwdriver and make sure all the screws are tight, especially the fan cage, then take a small crescent wrench and tighten up all the jack nuts on the back. The plastic ones tend to rattle loose. Hope this helps.

    If, after all this, you're still getting the whine, check your cables, your bass, everything...if it's still happening, take the amp to a tech.
     
  3. It does sound tube related. Probably minor at this point. Go get it checked out if you can.
     
  4. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks
    Sounds like you've got a microphonic tube. Turn the amp on, give it a reasonable amount of juice, and then tap on the tubes in the back with a pencil. You should hear some thumping through your amp on most of the tubes, but if you get a whistling sound or something like it, that tube is microphonic. Replace that tube, and you should be all good.

    Get a thick piece of foam or something and put it in between your head and cab, or put your head on some milk crates instead of the cab.
     
  5. Droog

    Droog

    Aug 14, 2003
    PDX
    Thanks guys. For some reason the thought of a towel or something escaped me. I hate setting that amp on the cab, but I have not other option yet. Hopefully its not a microphonic tube, but oh well if it is, simple fix. I just thought of something else to try. I have been using input 2, I'll try input 1 and see if it does it. That will help narrow down the problem.
     
  6. Ty McNeely

    Ty McNeely

    Mar 27, 2000
    TX
    Totally unnecessary unless the sound is more than you can bear. Usually at playing volumes there's no way you can hear the tube.

    Microphonic tubes are nothing more than a slight nuisance, but there's nothing really wrong with them nor any reason to replace them.
     
  7. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks

    Ummm.... if a tube is microphonic, it is generally pretty annoying. Regularly changing your tubes isn't necessary, true, but if one is acting up it should be changed.
     
  8. Ty McNeely

    Ty McNeely

    Mar 27, 2000
    TX
    Well, I've had a microphonic tube in my 300T since the day I got it, but at playing volumes its generally not noticeable at all. A truly microphonic tube will usually only resonate around certain frequencies as well.
     
  9. Wrong. Microphonic preamp tubes are an annoyance, yes, but microphonic power tubes are dangerous. They literally pulse voltage with vibration and are much more likely to short and do a buttload of damage to the amp. Even if they don't short, the voltage pulses can seriously heat up your output transformer since most of them aren't easily reproduced by a speaker and can damage it as well.
     
  10. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks

    Hooray! I was right for once! ;)
     
  11. Ty McNeely

    Ty McNeely

    Mar 27, 2000
    TX
    Hmmm.....


    :)

    Assuming that it is indeed pre-amp tubes as he thinks it is, he has no reason to worry.

    I assumed he knew the difference between preamp tubes and poweramp tubes, so I answered in response to the question.
     
  12. Suppose it's NOT the preamp tubes?
     
  13. Ty McNeely

    Ty McNeely

    Mar 27, 2000
    TX
    Then obviously he should replace them :)


    I'm not trying to say that you're wrong---I know beyond a shadow of a doubt that you know more about tube amps than I will ever know. Just saying that I answered the question he asked given the information he provided.

    Sorry to lead anyone astray.
     
  14. Droog

    Droog

    Aug 14, 2003
    PDX
    Have not had a chance to check the tubes yet. However I am still leaning towards the Pre-amp tubes. Especially being as channel 2 has original Mesa'a while Channel 1 and all the power tubes have JJ's. Imagine I should just get a couple more JJ 12AX7s for channel 2 anyhow.