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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