Funny Noises in my old SVT

Discussion in 'Amps and Cabs [BG]' started by SuperDuck, Apr 13, 2003.

  1. SuperDuck


    Sep 26, 2000
    I noticed a new noise coming from my 70's SVT. Have you ever had a guitar amp with a crappy spring reverb and tapped it with your hand? You know that echo-y internal noise you hear? That's what I'm hearing in my amp. I'm thinking of moving the head off the cab, as vibrations seem to cause this noise, as well as tapping the head or front plate itself. Playing loud, especially low notes, will set off this noise, which will last for a second or almost a minute. When the noise stops, it stops short, like it's cut off by some kind of gate.

    This is annoying, as I'm going to need it for my new band's first gig, which is on May 10th. I don't have time for it to sit on the tech's shelf for a month. Any ideas?
  2. One or more of your preamp and possibly your power amp tubes has become microphonic. Generally, the 'echo' indicates a preamp problem; power tubes usually have more of a 'roar.' The diagnostic procedure is the same for both sections with the amp running, tap each tube with a Sharpie. They'll ALL ring to small degree, but when you get to the offending tube or tubes, they'll produce the noise you've been hearing. The offenders will have to be replaced.

    I also recommend you get some sort of shock isolator for the head if you want to continue using it on top of the cabinet. The chassis IS shock mounted but the rubber wears out after all the years and the shock mounts don't work anymore. There's also the possibility that they've been removed entirely. About half of the SVT's I've seen have been missing their shock feet. If you have pics of the bottom of yours I can tell you instantly whether it has them or not.

    You can get by for now with the tubes you have by simply getting the head off the cab, but in the long run, those tubes need to be swapped.
  3. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    Just want to add that you should check the 6C4 first and go from there. The 6C4 is a pesky little bugger...
  4. MrGump


    Apr 20, 2000
    I have old SVTs,ad I agree with PBG(hi!).
    Ive also had an old Ampeg GeminiII that had a similar problem,and it was a leaky cap.Check the tubes fost but inspect the caps if the tube isnt th culprit.
  5. I worked on a Matchless DC30 one time that had a dried out, but functional rattling filter cap. It didn't affect circuit performance at all; the noise was purely acoustic, but the damn thing rattled in sympathetic vibration every note, sounded like a shaker. Weird!
  6. SuperDuck


    Sep 26, 2000
    You guys rock. :cool: Thanks. :)