Ampeg SVT-CL Tubes

Discussion in 'Amps [BG]' started by Dearthbass14, Feb 25, 2014.


  1. Dearthbass14

    Dearthbass14

    Joined:
    Jan 7, 2014
    So i recently just inherited an Ampeg SVT-CL head from a friend of mine and it needs a little bit of work. He told me the power supply needs to have a few resistors replaced and that it will need to be re-tubed. When i turned it on to try it i noticed that one of the 6 tubes was arcing. When i opened up the back to look at the tubes i noticed that 5 of the tubes were Genalex Gold Lion KT88's and that the one tube that was arcing was a Tung-Sol 6550. Is this an issue that all of the tubes are not identical? I know that the back of it says it has 6 6550's, but apparently this isnt the case here.

    Please help, this is my first tube amp so i am new to this!
  2. beans-on-toast

    beans-on-toast Supporting Member

    Joined:
    Aug 7, 2008
    I wouldn't run the amp in the condition that it is in.

    The SVT-CL requires a set of six matched power tubes. That's what you need to remember.

    They work together as a set of two trios. Each trio should amplify the same amount. When they do so, they are said to be balanced. The SVT VR has a pot that you can adjust to balance each trio, the SVT-CL doesn't have this feature. As a result, all six power tubes need to be matched and each trio needs to be balanced. Doing so optimizes performance and minimizes distortion.

    It doesn't matter that the tubes in your amp are different makes. What is important is that they are all matched. Based on what you said, it sounds like one tube is bad and that the plate or screen resistor (there is one for each power tube) on the power tube board needs to be replaced. These resistors are taxed and can blow like a fuse when a tube goes bad. It is important to replace them with resistors meeting the same specification as the originals. Some people use a higher wattage resistor to prevent them from blowing. You want the resistor to blow if the tube developed a problem. It saves blowing the output transformer.

    Buy your tubes from a reputable seller who tests the tubes, matches them properly, and offers a warranty.

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