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Ampeg SVT CL weird noise

Discussion in 'Amps and Cabs [BG]' started by jarrydee, Jul 25, 2012.


  1. jarrydee

    jarrydee

    Oct 22, 2011
    Michigan
    I just got this SVT CL and there is this weird noise coming through one of my speakers (410), it kind of goes away as I turn the treble down, I thought it was the tweeter at first but know now that it is not! It sounds kinda like if you tap a light bulb..ya know, you can kind of hear the elements inside move (springy). Any idea what this may be? If it is a tube, what one would you check first? Thank you!
     
  2. jarrydee

    jarrydee

    Oct 22, 2011
    Michigan
    ok, I can tap the top of the amp and it makes this noise. This stinks, I do not want to have to ship this big a** thing back...
     
  3. microphonic tube?
     
  4. jmattbassplaya

    jmattbassplaya Looking for a gig around East Islip, NY!

    Jan 13, 2008
    Long Island, NY.
    That's what I'm thinking.

    Take its backside grill off and turn on the head (while it's plugged into an amp, of course). Take a pencil or chop stick and lightly tap each tube. If one of them is microphonic you'll hear the tube make a noise through your speakers (it usually a higher pitched ringing sort of noise).
     
    quickfix likes this.
  5. jarrydee

    jarrydee

    Oct 22, 2011
    Michigan
    Thats what I was thinking, but this is my first tube amp so I really dont know for sure.where should I start first, the power tubes or the preamp tubes..or should I not do anything for now and see if since I just bought it maybe they will allow me to take it to be serviced, really dont want to ship it back. there is an authorized service center 4 blocks from me
     
  6. ↓
    ↓
    If that doesnt turn anything up take it to the local tech.
     
  7. jarrydee

    jarrydee

    Oct 22, 2011
    Michigan
    ok, thank you!
     
  8. jarrydee

    jarrydee

    Oct 22, 2011
    Michigan
    I tapped on the 2 tubes in the front case, one of them rang like a bell through my speakers. since there are only 2 of them I assume these are the 12au7's, could I use a 12ax7 in its place, or do I need a 12au7?
     
  9. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    If it's really ringing loudly like that, then yes it's likely the culprit. You need to place a 12AU7 in the 12AU7 slot on these amps, the good news is they're pretty cheap and easy to find. Those visible smaller tubes are your phase splitter/inverter and driver tubes. On the SVT-CL the pre-amp tubes are located inside the upper chassis, which you have to remove in order to get at those tubes. I was going to suggest swapping those around first before checking the driver/PI tubes, but if you found one that is pretty loud that could be the one to swap out.
     
  10. Alex1984

    Alex1984

    Jan 16, 2010
    Vancouver
    Yes, sounds like a simple pre-amp tube problem. But also, if you have ultra-hi on, and treble cranked, the SVT-VR is known to have a bit of a high frequency thing going on. I believe the same applies to older SVTs.
     
  11. hi, all help. i just got around to using an all tube beamoth svt classic head and at first i turned it on and there was just a red light from the standby switch working no matter how many times i let it set and warm up man i was totally steaming. then i saw the 3 prong plug wasnt attached well . it then clicked on. then as i looked over the back bias controls i saw one was green[right hand tube side and the 2nd was blank with zero green light. i pulled the grill off the back and made sure all the kt88s & pre-amp tubes were lit up and securely in right. then i put the screen back on and still no green light from the number two bias control. i adjusted it clockwise and got a red light to come on and then backed it down to where the red light went off into what should of been the green light zone. but no green light. am i in trouble here with no green light is it a burnt out bulb and well it effect my heads playability? number one bias control works as discribed from the manual . i get the red light then i back it down to get the green light. alittle worried about s/h Also. sorry for the extended drama here! can someone shed some support life on this issue for me please. thanks, mark.
     
  12. alex you there!
     
  13. hodgy

    hodgy

    May 5, 2004
    Bothell, WA
    Customer Support- Ampeg/ Line 6
    The 2 tubes in the preamp are 12AX7s.
     
  14. hodgy

    hodgy

    May 5, 2004
    Bothell, WA
    Customer Support- Ampeg/ Line 6
    Could be a bunk power tube, might be one of the 12AU7s. Could be one of the 220 ohm resistors on the tube board. Could be one of the 10 ohm resistors on the PS board. Could be one of the TL074s or the TL072 on the PS board. Start with the tubes. Swap your 2 12AU7s around and see if the bias fault follows the tube. If that doesn't solve the problem, Swap the 3 left-hand power tubes with the 3 on the right. If THAT doesn't narrow down the problem, it's tech time.
     
  15. jarrydee

    jarrydee

    Oct 22, 2011
    Michigan
    Thanks! Thats what it ended up being, all set! Thanks TB
     
  16. RiZzBot

    RiZzBot bass+beer+broken strap locks= :'( Supporting Member

    Nov 23, 2014
    210, Texas
    Sorry for resurrecting this old thread instead of creating a new one. I am having the same problem with the 12ax7 tube in my svt cl. It's making a loud high pitched noise with the treble cranked. After doing the pencil test I narrowed it down to the 12ax7 tube. makes a springy sound through the speakers when I tap it. What brand would you guys recommend replacing it with? There are a lot of different brands to choose from on ebay. I want to keep it as close to the one that is currently in there. Maybe @beans-on-toast can chime in on this one too. Thanks for the help. I included a pic of the culprit.

    [​IMG]
     
  17. I would just find a cheap one and see if that isolates the problem.
     
    RiZzBot likes this.
  18. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008

    Here is a guide as to when to change your tubes: How Do I Know When to Change My Tubes? The sound of the amp will change with time. Even if certain tubes are not bad, the performance of the amp can decline. I'm not saying to change them all, just keep it in mind.


    Note that there are small signal tubes in the preamp as well as in the power amp. To access the tubes in the preamp, you have to remove (or partially slide out) the top chassis. The three that you are looking at are in the power amp. If they are all old, it is possible that others might be worn out.

    Yes, it sounds like the tube needs to be replaced. At least that's the first thing to try.

    I don't recommend buying a tube on ebay unless you know the seller. It can be risky because you don't know what you are getting. Tube resellers buy in bulk, test their stock for things such as noise, microphonics, cathode current, and transconductance. Tubes that don't measure up are sold off and many wind up on ebay. A lot of people don't have issues with ebay tube purchases, just be careful.

    A good reseller will burn in their tubes to weed out early failures, then test them, and offer a warranty. I recommend http://www.tubesandmore.com but there are other good places. If you want NOS, http://www.tctubes.com is a good place.

    Ampeg used Sovtek 12AX7-WA tubes, they also used JJ preamp tubes. If you want as close as possible to what you have, try one of those. If you pull the tube, you may be able to read the label and see what it is. They compare different makes of 12AX7 tubes here: Tube Store 12AX7. If gives you some idea as to their differences in sound. In general, more expensive tubes are more popular and sound better.
     
    RiZzBot likes this.
  19. RiZzBot

    RiZzBot bass+beer+broken strap locks= :'( Supporting Member

    Nov 23, 2014
    210, Texas
    Thanks buddy! :D
     
    beans-on-toast likes this.

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