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HELP! Tube/SVT gurus needed!

Discussion in 'Amps and Cabs [BG]' started by Nick man, Apr 21, 2006.

  1. Nick man

    Nick man

    Apr 7, 2002
    Tampa Bay
    I just flipped on my old SVT and saw a BRIGHT blue flash followed by the amp turning off. The fuse is blown and instead on being a 10A 125V fuse it was a 15A ?V fuse.

    I couldnt find the right size fuses at the local Radio Shack but even if I do find them should I even try turning it on?

    Also it was tubbed with KT66's and one of the tubes is loose between the glass bulb and its base. None of them look like they have any problems otherwise.

    I'll bring it to the shop on Monday but if there is any extra diagnosis I can do before that Id like to.

  2. syciprider

    syciprider Banned

    May 27, 2005
    Inland Empire
    You accidentally activated the onboard pyro huh?;)
  3. barthanatos

    barthanatos Insert witty comment here

    Feb 8, 2006
    South Carolina
    No, don't turn it back on. Something made the fuse blow.

    Maybe that loose tube that you mentioned? Try replacing that. Make sure you only put the correct size fuse back in. The flash of light was something turning into charcoal (maybe), but was not the fuse blowing. If you had the proper fuse in there to begin with, it may not have melted whatever made the flashy-light.

    If you are the type that takes expensive fragile things apart, you could take a look at the circuit boards and see if any resistors or anything are fried. Then you could de-solder the bad resistor, figure out which one it was, and solder a new resistor in place. There's schematics available if you search here. But... you could just make things worse. But... it is pretty quick and easy if you have some basic knowledge, it is interesting to poke around even if you decide not to do anything, and you could save some serious bucks.
  4. Piece of advice i was given about mine

    "Its an ampeg, its an SVT, you only have to worry about something being wrong with it if it A) Makes funky noises it shouldnt or B) Makes funky colours it shouldnt "


    I would get it checked out, if its one of the internal fuses maybe its a slo-blo one? Im not sure tho

    - Will
  5. Nick man

    Nick man

    Apr 7, 2002
    Tampa Bay
    Is there a chance that I blew a transformer or something else hugely expensive? It is going to the shop on Monday, but Im kinda curious.
  6. Nick man

    Nick man

    Apr 7, 2002
    Tampa Bay
    Oh, and when I bought it, it was loaded with KT66's. Could that be what caused this?
  7. tadawson


    Aug 24, 2005
    Lewisville, TX
    This is either due to a short from something like the tube with the loose base (if it got twisted), or a bad cap or something. Typically, resistors smoke, caps smoke, transformers either go silently or burn - typically the only thing that will flash blue is something arcing over, so you may not find any bad parts - just something that got too close to something else . . . . Tube gear is pretty rugged, to it's probably that the problem is pretty minor, and that the fuse saved you. Since just about every "burn" part is inside the chassis, for you to see a flash, it would almost have to be a tube arcing over inside. Any chance one is cracked and got air in it? That would do exactly what you describe, and should be correctable with no more than a fuse and a new tube . . .

    - Tim
  8. timv

    timv Supporting Member

    Jun 7, 2000
    Chandler, AZ
    kt66's or kt88's? If they are kt66's they should not be in there. The amp is made to run 6550's or kt88's. The amp runs at almost 700 volts and I am not sure if kt66's can handle that, especially if they are newer ones. Definately get it checked out and if those are kt66's plan on a power amp retube....
  9. Nick man

    Nick man

    Apr 7, 2002
    Tampa Bay
    They were OLD KT66's . I didnt realize it untill now.
  10. barthanatos

    barthanatos Insert witty comment here

    Feb 8, 2006
    South Carolina
    I personally saw a flash of light from a resistor going. But that was when I had the chassis open. I almost certainly wouldn't have seen it if the covers were all on.
  11. ibz


    Apr 14, 2005
    Columbus, OH
    Just be careful of those very harmful voltages that can be stored if you go poking around in a tube amp. If you don't feel comfortable doing it, you probably shouldn't.
  12. barthanatos

    barthanatos Insert witty comment here

    Feb 8, 2006
    South Carolina
    Indeed. They are stored by capacitors. Not sure how long they will be in there after you turn the thing off. It is possible to discharge capacitors. Where I work they have this copper stick thingy with a glass handle that has a braided copper wire running of of it to a clamp. It's used for just this purpose, though I'm sure you could find something similar. You clamp it to ground and then touch what you want discharged (edit: you touch it with the thingy, not with your hand). Just realize that, depending on where you are in the circuit, you may have to do this at several points in order to make the amp safe.

    You can also check for stored voltages using a volt/multimeter.

    disclaimer: make sure you know what you are doing. I am not an electrician nor electronics tech.
  13. Nick man

    Nick man

    Apr 7, 2002
    Tampa Bay

    Any more info?

    I found out that the KT66 tubes in there were Genalex Gold Lion and Gold Monarch. Aparently worth a good chunk of money if they are still good.

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