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Question for the SVT / Tube gurus

Discussion in 'Amps and Cabs [BG]' started by fishinmuzician, Apr 8, 2005.

  1. I have a 5 yr. old SVT-CL. Recently it has been producing a slight noise .... almost sounds like something rattling in the speaker cab ... that only occurs when an "A" note is played. Open A or 1 octave up is most noticable. It isn't loud enough to be heard at all when playing with the rest of the band, even at very low volume. Anybody run into this before?

    The cabinet is fine, the ohm setting is matched. Is it pre-amp, driver or power tubes? I would sure prefer a quick fix instead of the repair shop or all new tubes!!
  2. Hmmm...could be a tube is going microphonic and is sympathetic to vibration at a certain frequency. Try tapping on the tubes with the eraser end of a pencil. Like a bad tooth, the offending tube should cry OUCH!
  3. metron

    metron Supporting Member

    Sep 12, 2003
    In my experience (which is very little) microphonic tubes make a very distinctive pinging sound unlike anything Ive heard before. That may be it but your description "rattling in the speaker" makes me think you may have a screw loose on one of your drivers or something.
  4. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Rattling might be cabinet, looseness or maybe an air leak.

    Could be tubes, but 12AX7 etc typically do "boing" as opposed to rattle.

    Output tubes have been known to sort of "chime", which could be like a rattle, depending. Can sound like shaking chains too.

    You could always try tapping on the tubes one by one.

    Or, just as a first check, put the head somewhere other than on the speaker. See if you still get the noise the same.

    If so, look at speaker.

    If NOT, might be the head, try it back on top again to make sure you still hear it..

    If it is an output tube, you may be able to just replace the one, depending if you have graded ones in now, and can get the same grade number as a replacement.
  5. Guys, thanks a bunch for the info. It's definitely not the cabinet. I've tried it with my GK 400-RB and (nasty "B" company) BX3000T. I guess it could be more like a chime or slight chain rattle. I'll try tapping the tubes & see what happens.

    Also .... where's the best place to get replacement parts for the old guys. I have a '70 original SVT that needs some new tube sockets and a few other items.

    Thanks again!!!