I am a big fan of the KT 66 tube. It is, along with the similar 6L6 tube, a full bodied, harmonically dense sounding tube that does does not have a hard or harsh edge to the sound. The only pentode/tetrode tubes I like more are the exotic Western Electric tubes such as the 350 B and 349 tube.
Groove tube kt66
Was on the hunt for a octet of el34,s for my Prima Luna evo 400 and was finding either empty shelves or outrageous prices. A small local shop here in So Cal that I like had an octet of JJ or I guess “Groove tube” kt66,s, I was leary of this tube its all over the web because it just seemed to me it was more of a guitar amp tube. Wow pleasantly surprised,at startup I was a little worried but within an hour or so it really settled down and started to sound nice. Ive used el34,s in this amp exclusively since I bought it so Im not sure if its the fact thats its a KT66 and different or just a nice sounding tube but I,m diggin it pretty much right out of the box , just thought another member might have seen this tube and been skeptical like I was. Happy listening!