The reason why I ask is that my amps use 8 KT88s per side. I purchased 8 matched quads, that I hoped would serve me for a long period of time, I have to now dip into the 2nd set of 16 to replace 3 that look like there are not doing well. I have an odd set of 3 of another ilk, that if used would keep the 2nd set intact.