the "original" in my case was Sovtek 6L6GC and any new tube was better !
With the KT-77 i would think your sound will be good and that unless you hear different ones , not be able to evaluate any different tubes.
Yes with the KT120 you cannot put the cover back on so that is out . if you are trying 6l6GC the 6n3ce is a far cheaper And better option. I am pretty confident this will be better than the GEnalex KT77 as well ..a s in my case i prefer the larger freq extension of the 6l6GC to the lushness of the KT77 (or EL 34) but individual tastes can vary hence cannot say how it will work for you
With the KT-77 i would think your sound will be good and that unless you hear different ones , not be able to evaluate any different tubes.
Yes with the KT120 you cannot put the cover back on so that is out . if you are trying 6l6GC the 6n3ce is a far cheaper And better option. I am pretty confident this will be better than the GEnalex KT77 as well ..a s in my case i prefer the larger freq extension of the 6l6GC to the lushness of the KT77 (or EL 34) but individual tastes can vary hence cannot say how it will work for you