I noticed on the Apos tube site they claim that 5% of these tubes when tested meet their criteria. This means that whoever is manufacturing these tubes is so bad at it that 95% of them are rejected by Apos (sorry about the redundancy). Rest assured that I'll never buy anything from these guys. I've used lots of different tubes in my amps over the years and Gold Lions seem to be the most reliable and best sounding over all.
KT88 Tubes
I am new to tube amps having acquired a Harmon Kardon Citation II about a year ago. A little while ago I started experiencing one of the channels dropping out and an occasional loud pop. Today I noticed one of the KT88 tubes glowing purple where the rest glow orange so I have assumed that the tube has gone bad. As I bought this amp used, I have no idea of the age of the tubes. So I have a couple of questions. First, should I replace just the two tubes on the bad channel with a matched pair, or should I replace all 4 tubes with all 4 being matched. Second, any recommendations for good quality KT88 tubes? Any other thoughts or ideas would be appreciated.