For the past 2 years I have been using a Shindo Montille 6V6 amp and it is a sweetie, putting out 12 or 15 watts, depending on what you read. It came with United Electron 6V6GT tubes. Since I have no idea how old the tubes are, I started questioning if new tubes might sound better. After a lot of research and talking to 2 Shindo dealers, I found I could not simply order a set of NOS tubes from Shindo. One of the dealers recommended a type of NOS he felt was the best of all, but the quad I found was about $400, which is out of my range at this time - I have spent way too much on gear in the past couple of months. I looked around and settled on a matched quad of Tung-Sol tubes for $80. Out of the box they sounded a bit strident, so I pulled all the silver interconnects and put in copper, which helped a bit. Finally I decided to test everything on my old, simple Knight tester. All it tests is for shorts and the dial says bad or good, higher scores presumably being "gooder". The Tungsols all tested at about 70 on the meter, the United Electrons about 90. One of the UE tubes was a bit weaker, but I had 1 NOS UE 6V6GT that tested the same as the best of the used tubes. So now I am using the 4 best United Electron tubes, which all had similar "gooder' scores. I did replace the 2 6AW8 tubes with new ones which had higher scores. I put the new Tung-Sol 6v6 tubes in storage as backup in an emergency. Now the little sweetie is singing sweeter than ever. Is it common for old tubes to be stronger as mine are?