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Older SVT making strange noises...

Discussion in 'Amps and Cabs [BG]' started by Chris Breese, Apr 3, 2006.

  1. I have a mid '70s SVT, and when I take it off standby and just let it sit there, it makes some pretty strange noises through the speaker. Lots of wooshing sounds, high pitched electrical noises, and the sort.

    Anyone know what's causing this?

  2. It probably needs recapping.
  3. Cool...
    Thanks a bunch!!!
  4. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    BTW, the caps in question include the "coupling" caps between stages. Specifically the ones from the "plates" of the preamp tubes.

    Not just power supply caps.

    The direct problem could be just one part, but if someone has to get in there and work on it, they may as well do a solid job of it.
  5. timv


    Jun 7, 2000
    Chandler, AZ
    I've had bad preamp tubes cause the same kind of sounds. Could try changing one at a time and see if it goes away when one is replaced. Also, could be a dirty send return jack on the back. I have worked on a few different amps now that had similar issues that it was just a dirty jack.
  6. Come to think of it, I had that very problem with one of mine. Turns out it was a Mullard 12DW7 that had split its seam lengthwise and was gassing.
  7. Well...that narrows it down...:meh:
  8. I got similar wooshing sounds with my SVT-2 when it was needing repaired, one of the power tubes was completelly dead when the tech tested it (the others were on the way out), and if i remember correctly i think there was one of the 12AU7 driver tubes was microphonic or just screwed and making noises like that too
  9. All righty then!!
    Sounds like the bench time is going to add up trying to figure it out. :meh:

    I must say that it's all worth it, because the tone and power this thing has is unbelievable, especially through an 8x10.
    :cool: :bassist:

    Anyone ever heard of International brand tubes? This SVT has 6550s of this brand. They say 'made in China,' but I haven't heard of them.

    Thanks for all the help!
  10. Ive had "National" branded preamp tubes, they were crap that was in my SVT-II when i got it, they were made in china too, dont know if they are from the same company or not
  11. International C Servicemaster tubes. They have a shouldered bottle. Anyway, I think I'm going with Sovtek 6550WE's soon.
  12. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    National is a brand that was distributed by Richardson Electronics, in the US. They also distributed National "gold" branded premium 12AX7s etc.

    Basically tested chinese tubes. Richardson is an industrial tube supplier, and actually do (did?) make thyratrons and other industrial tubes for welding etc.

    I think at one time we DID get 6550s from them, I know we were getting 12AX7s (I had to visit them and work out the testing), but I don't recall the tubes being anything particularly great......... but they were "available". That was quite a while ago....... might be some old tubes if they were original.

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