I have a CJ 12L and have been swapped several types of tubes in and out, and have listened for noise. It's proven to be a very quiet pre amp. Tried you different tubes with dampers? Dave
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You will get some tube hiss but should only be audible when you put your ear up to the speakers; say about a foot away. If it is audible from your listening chair, say 10+ feet away, then you probably have a noisey tube. Does it come from one channel specifically or both? I believe that unit only has one tube per channel, two total, so you may want to repace both especially if it is a used unit and you don't when the tubes were last replaced.
If it makes you feel better, I hear the same type of hiss about 1 ft away from my SS pre when I turn the volume up enough. From my listening position it's inaudble, but I know it's there. I think it might be a characteristic of all systems. The only times I've heard a truly "black" background were in systems with monster monoblock amps (500+ watts) that were just loafing along. It's one of the benefits of headroom. The other spot to look is the recording. Some Cd's seem to be louder then others and don't need to be turned up as high, and thus, less hiss.