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Ampeg svt 2 pro bias issue

Discussion in 'Amps and Cabs [BG]' started by danielmarechal, Mar 31, 2015.


  1. danielmarechal

    danielmarechal

    Mar 31, 2015
    USA
    Hello there.
    Just bought a used ampeg svt 2 pro. the bias 1 is correctly, Green Light and then Red light turning clockwise. and when amp is without signal, only green led is lit. OK

    The problem is with bias 2, it is red light and when I turn clockwise i got both up, red and green

    I read the manual and it says : Red comes on, Then green = Set Slightly before green comes on, obtain matched tubes when possible.

    I read many threads here on talkbass but didnt find anything about red then green, only stuff about green light didnt appears.

    I did some tests swapping the 12au7 from bias 1 and it didnt work!
    sorry about my bad english, Im not from Usa. Just spent a lot of money on that svt and im afraid!
    Thanks alot!
     
  2. hodgy

    hodgy

    May 5, 2004
    Bothell, WA
    Customer Support- Ampeg/ Line 6
    Swap the 3 left tubes with the 3 right tubes and see if the problem follows. Most likely you have an issue with a power tube. It's probably a good idea to just retube the output section, especially since you got it used.
     
  3. danielmarechal

    danielmarechal

    Mar 31, 2015
    USA
    hello, thanks for comin!

    I did swap 3 left with 3 right , and the problem is now at the bias 1!

    Here in brazil is very expensive a 6550, its a good ideia buy only one and make some tests? or better ideia is replace all 3?
    thanks
     
  4. hodgy

    hodgy

    May 5, 2004
    Bothell, WA
    Customer Support- Ampeg/ Line 6
    The 6550s are expensive in the United States, too! I recommend replacing all 6 power tubes with a matched set, as this type of circuit works best when everything is balanced. Some folks on here might recommend only replacing the group of 3; this will get you by, as you can adjust the bias to balance things out- however, it's possible that even though your bias now looks good, the 2 sides may not be exactly balanced. This could work for you for a long time, until eventually one side or the other fails. I totally DO NOT recommend just replacing one tube. You'll just end up with the same problem over and over again. But you might get lucky.
     
  5. danielmarechal

    danielmarechal

    Mar 31, 2015
    USA
    thanks alot for the help .
     

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