It is hard, if possible, to give you an intelligent answer. Differences between some brands of 6550's and differences between some brands of KT88's can be as great as the differences between the 6550's and KT88's. Generally speaking 6550's are more linear and KT88's are more colored, but there are a lot of exceptions to that generality.
I think you would get more meaningful responses if you were to indicate exactly what about your present sound you wanted to change or improve and identify the brands of tubes you are now using.
If you can't do that you are flying in the dark.
I think you would get more meaningful responses if you were to indicate exactly what about your present sound you wanted to change or improve and identify the brands of tubes you are now using.
If you can't do that you are flying in the dark.