They are Sylvania copies and if your amp is biased correctly they sound quite good. My Mesa boogies ( older mark series ) are fixed bias and the run cold which i like, if your amp is biased to hot for any tube it can sound muddy and pretty much like crap. Shuguang preamp 80's 90's era and 70's 80's Sylvania's are my favorites, i run sylvania 6CA7'S in my 73 Marshall and they sound killer, these bugera copies are not bad with the right amp and correct bias and ive not had one fail yet. Tone is subjective so everyone has a different sound they are looking for. Bugera may have cheap amps but just because there name is on the tube doesn't mean it's cheap or inferior. just my thoughts.