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SVT2 whooosh sound happens when taken off standby

Discussion in 'Amps and Cabs [BG]' started by svtb15, Feb 28, 2006.


  1. svtb15

    svtb15 Commercial User

    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    When I turn the SVT2 non pro to ON, and wait a minute or two,then take it off standby a weird almost rushing wind/ ocean sound is emmited from the speakers...After about 10 minutes it goes away.. I thought it may be a preamp tube.. But then I tried and wiggled the 12AU7 driver and it made that noise.. So i cleaned the socket and pins on the tube and reset the tube... sound goes away.. but it may also be heated up by then. i am thinking. if i wait 2-3 hours and turn it on again it does not do it.. but if I wait overnight it does..
    I turned the amp on today it did the same whoooshing/ static/ like a river rushing sound for about 5 minutes and then slowly disapated.. I also thought that it may be condensation somewhere in the chasis but i am at a loss..
     
  2. Some tube(s) is(are) bad.
    You'll have to do some investigation to see which one it is, try by the pre and walk your way to the power (but I doubt the power tubes at this point).
    Buy yourself some 12AX7 and 12AU7 and swap them one by one.
    It will be cumbersome.
    Make sure you let the filament warm up for the same amount of time (ie, before turning standby off).
     
  3. svtb15

    svtb15 Commercial User

    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    yes .. that is what i thought too.. Thank you for your fast reply.. it started to happen all of a sudden. the pre tubes are only about 1 month old too.. in your opinion do you think it could possilby be the driver tube or inverting tube the 12au7 or the 12ax7 that are right before the 6550s that could also cause that... I have a load bank set up so i can rebias it , which will need to be done if i swap out the driver and inverting tubes.
    Thank you in adavance..
     
  4. What you describe sounds like power tube microphony. Just by messing around with the preamp tubes, you may have inadvertantly moved the offending power tube(s) into a position where it(they) doesn't ring.
     
  5. I had this problem, well, a similar one, also, whenever i played an A i got infinate sustain, (I had to turn the amp off to get it to stop :( )

    Full retube sorted it for me tho
     
  6. svtb15

    svtb15 Commercial User

    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    I just retubed the whole amp just a month or so ago... So today i pulled all of the preamp tubes and driver tubes and put the old ones back in. Still did that wwhoooosh ocean sound... I just received by fedex today a new set of 6550 for my 70s SVT that i am retubing and figuged i would try them out just to see.. well it still did it... so i got some contact cleaner and cleaned all of the tube sockets, retensioned the sockets, let it dry out for about an hour then poped back the new 6550s and all the new pre tubes,turned it on and the wwhooosh is gone... must have been a dirty socket??? so after that i let it warm up for about a good hour and biased it and set the phase inverter.. sounds great now.. I want to see what happens when i let it cool down over night and turn it on tomorrow if that sound is gone.. because it would stop by fading away when the amp was warmed up.. lets see what happens on a cold startup... i really cant complain though, i got the amp new in 1989 and have used it ever since without one problem, lucky for me i do almost all my own amp work as a hobby, so recapping and bias is no sweat...but since i am not a pro and just a hack tech,i have to ask millions of questions from folks that know more in hopes that i fix it... thank you very much
     
  7. That may have been your problem right there. A loose socket will let power tubes rattle.
     
  8. svtb15

    svtb15 Commercial User

    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    Well.. i turned the SVT2 on from a cold start after sitting all night ... and it is doing it again..mmmmmm.. i am stumped because I would go with the Diagnosis that you gave 10000%... so i am stumped.. I put all brand spanking new Winged C 6550s and switched out one by one pre tube with other ones that I have including the 12au7 and 12ax7 driver tubes and when I turned it on it did it again.. after about 10 minutes it fades away.. So i think it is a heat issue... but where???

    My next thing to try today is pull the bottom, Discharge the caps and check for any cold solder joints that may be moving in microscopic amounts. That is all I can think of to do...
     
  9. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    This could also be a capacitor with excessive leakage. When they are on "the edge" they tend to form back up when under power, and it may just be that the 10 minutes is how long it takes this one to "be happy". Not an expensive part, but finding it may be a bit time consuming.

    Does this problem occur if you run the amp without the preamp tubes inserted? Keep pulling tubes moving from front to the back (power amp) end, and when it quites, you have found the stage the noise is coming from . . . . . .

    - Tim
     
  10. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    tadawson has the right idea.

    I was thinking leaky cap, or loose connection. Probably either the "forming" mentioned, or else something that is corrected when it heats up, typically a loose connection (possibly inside a part). The 10 min is about right for most parts to have warmed up to operating temperature.

    Usually a part that "re-forms" is good for a while, even after being off. But there are exceptions to everything.

    If the noise continued, instead of stopping, or if it would come back, I would have suspected what I used to call "fenderitis", which is usually a plate resistor going bad and being noisy.
     
  11. svtb15

    svtb15 Commercial User

    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    MMMM. i will try running it without the preamp tubes plugged in.. I have not done that yet.. i will do that most likely tonight..and if you dont mind i will respond with my progress.. I am really thankful for all your help.
    I guess I can try replacing those pesky to remove filter caps.. afterall they are original from 1989... But I am going to look for cold solder possibly by output jacks first...that is the only design flaw that I can see in that amp.. the speaker jacks being mounted to the PCB.. that is an accident waiting to happen... and if i remeber the screw to the DI out has one short and one long because it gets real close to tracks on the PCB.. it has been years since I had it open... I will give an update on this one tomorrow..
    AND from Gut instint at this point i tend to think you are both right about a possible leaky cap... I just wonder if it comes down to it, should I start with the Power supply caps first?
     
  12. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    That's why I said leaky cap. He said that after being off for 2 to 3 hours it won't do it, and it should be totally back to room temp in that amount of time. Granted, most leaky caps last longer, but I can't see a thermal cooling for 3 hours and not coming back . . . but that's not impossible either . . .

    - Tim
     
  13. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX

    I would be inclined to vote AGAINST the filter caps - if they get too leaky, the fuse blows, or they vent. Otherwise, failing filters just give hum. Sounds to me like you have a cap going in a driver stage . . . not preamp, 'cuz you don't say the noise is that loud, and I doubt power stage, 'cuz there typically aren't that many caps in that area . . .

    - Tim
     
  14. Caeden

    Caeden

    Nov 24, 2007
    svtb15, did you ever get this issue resolved? My SVT-II is doing the same thing..
     
  15. WingKL

    WingKL

    May 12, 2007
    There one sure way to track down the source of the noise and that's with a oscilloscope on it's AC input setting with the live circuit. Start at amp input and work your way through the gain stages till the output transformer. Not the safest thing to do on a high voltage tube circuit but if you are careful and keep your free hand and the rest of you body away you'd survive. Either that or let a tech do it.
     
  16. svtb15

    svtb15 Commercial User

    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    wow how time flys.. it must have been 3 years since my post..
    i have been using my Genz Benz gear the past few years...
    i have not used the SVT since... its (the svt) in storage right now.. before i retired it. .i did a full recap and retube and it never did that sound again.. dont know if it was the recap or the retube that got rid of the problem..


     
  17. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Dang Kirk, by the time you get to playing it again, it's going to need more new caps!
     
  18. svtb15

    svtb15 Commercial User

    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    so true...
    but my back is so messed up.... just the thought hurts;)



     
  19. Caeden

    Caeden

    Nov 24, 2007
    the thing is, I had it re-tubed recently.. tech said there was a bad connection somewhere cause everytime he tapped it with a stick, the oscilloscope would show the signal go all wonky.. he never got around to taking it all apart and looking at it. Now as soon as I turn it off standby, theres the whoosh/static sound, and its distorted. Sometimes it stops after a few minutes and its fine.. :meh:

    been using the Trace AH350X as backup, but im really missing the SVT-II..
     
  20. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Why wouldn't your tech fix that for you?