I was curious to know how closely matched the stock KT88s in my R8 were so I asked Tube Labs if there was a method to roughly check this when you don't have access to a tube tester. This is the method they suggested. A) Let the amp warm up then set the bias on V1.
B) Switch off the amp and switch V1 & V2.
C) Switch amp back on then check the bias on V1 and note its position.
D) Repeat steps B & C but with V3 then V4 in the V1 socket.
Here are the results I got as displayed on the R8s bias meter. I also purchased a matched quad set of TAD KT88-STR tubes and their results are also displayed below:
That is actually a great way of testing them! What matters most is the tubes on the same channel of a push pull amp match. Left to right isn't likely to be noticeable.