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SVT-CL "pop" and fault light flash = bad tube?

Discussion in 'Amps and Cabs [BG]' started by Mastermold, May 2, 2015.

  1. At tonight's gig, Heritage SVT-CL, turned it on, warmed up a minute or so, flipped the standby and "pop" and the fault light is all I got. Turned it off/on a few times after letting it sit but did the same thing.

    Sound like a power tube? I've never worked on my own amp so I'll need to send it to a tech. Anyone in OC California you guys recommend?
  2. Sounds like a power (output) tube failed. Don't know people in CA anymore but if you make a trip to Thousand Oaks PM Johnk_10.
    Mastermold likes this.
  3. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Tube replacement isn't brain surgery. You can do it yourself pretty easily unless you blew a resistor that acts as a power tube fuse. But that usually doesn't happen.
  4. John's restoring a friend of mine's bass, might make a trip with him.
    beans-on-toast and B-string like this.
  5. Embarrassed to admit I don't even have backup tubes to try, but you're right I should learn.
  6. jastacey


    Feb 8, 2009
    Sometimes when a tube fails in a SVT-CL it will take out the some other components (220 ohm screen grid resistors), best take it to a tech who knows SVT's
    beans-on-toast likes this.
  7. jason the fox

    jason the fox Often rocks and rarely rolls.

    Jul 2, 2013
    Nova Scotia, Canada
    I don't have a Heritage, but I have 'regular' SVT-CL and I had the exact same thing happen. It was indeed a blown power tube, and the tube in question actually flashed blue when I flipped off the standby switch. I just bought a matched set of 3 to replace the triad that had the blown tube. I posted a similar thread when I had my problem, and general consensus was no need to replace the whole tube compliment.
    Mastermold and JimmyM like this.
  8. So the closest tech according to Ampeg's website is Ampwerx Repair in Long Beach, CA. But I'm thinking about trying a tube swap (or 3) first just in case that's all it needs.
  9. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Most likely it's only one tube, yes, but it's best to replace the triplet set to keep matching so it'll bias correctly.
    jason the fox and Mastermold like this.
  10. Cool, I'll give it a go. And I should have backup tubes anyway.
    jason the fox likes this.
  11. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    OK, well then I should mention that the triplet sets are arranged in triangles, not rows.
  12. Finally got around to taking this one to a tech to figure out what the deal is (been using my other SVT so wasn't in dire need in the interim). Looks like you guys were right that guessed it was perhaps a blown resister. The tech installed new JJ tubes and found one was not conducting and he couldn't get a green bias light on the side that controls that tube. It is in the same position that the shorted tube was in and his initial tests showed no screen voltage on the tube. So he thinks it's most likely a blown screen resistor but he still needs disassemble the amp and verify. He said this is a fairly common problem with the SVT’s, explaining the resistor will act as a fuse and blow to prevent excessive current from destroying the output transformer or frying the circuit board. Should have the SVT back later this week, it's been my #1 so I'm looking forward to getting it back in service. Don't have a gig until Sept. 18th so I've got plenty of time to play with it before then.
    beans-on-toast and B-string like this.
  13. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Changing the screen resistors is a bit of an inconvenience but they do blow to protect the amp as your tech explained. Sounds like the they will have your amp back in service before long. Any time a power tube blows, they should be checked.
    Mastermold and B-string like this.
  14. Fully agree.
    Mastermold likes this.

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