KT150 Tube Matching

 Tubes need to be burned in a bit before matching to get a close match. Otherwise they can drift apart as they burn in leading to a poor match. I believe Upscale does this. I know Jim McShane does. The last 2 quads of KT120s I got from him were dead on. Next to no drift. I did not have to adjust the bias again after the first check. 

Most Audio Research amps and I am sure others, run the tubes in pairs. There is one driver tube for each pair. While you can check the bias of each tube, you bias the pair with one pot. So you want closely matched pairs of tubes. You don't want to have one tube bias reading really low while the other is high.

 You need to check the bias often when you replace power tubes. The bias will drift as they burn in. You don't want a tube running really hot for a long time. They will settle down as they burn in. This is a lot less of an issue if you get power tubes that were burned in a bit before matching. They won't drift nearly as much.

 I don't know about paying extra for platinum matching and such. I just email Jim McShane. Tell him I need two quads of the power tube I want. I also tell him what amp they are for. His tubes are fairly priced and I have never been disappointed Yet. I have been buying tubes from him for nearly 20 years now.