I have never used any JJ 6L6GC's, however if they are like any of their other tubes then I would say they are good. Replacement may depend on a few things like how long have they been in the amp and how often do you play, have you noticed a change in tone, output, etc? You may want to try some Sovtek 5881's should you decide to replace the tubes and want to try something different. The Sovtek is a well-made tube with great saturation and are affordable. I like them, but you may not.
