Nsgarch, I think your right, but when each tube can be individually biased doesn't that overcome the problem you bring up? You not only set the initial bias but you can monitor it and adjust it VS getting a matched quad in an amp with auto bias which has no provision in the auto circuit to adjust the bias each tube automatically.
Its my understanding that 'matched' tubes don't necessarily wear evenly and at some point in time you will have the same problem of the tubes not being 'matched'. In an auto circuit you have no control, whereas when you can adjust each tube individually you can monitor and maintain a balance between the push and the pull tube(s).
Anyway thats how I understand it and it is why I prefer an amp which has manual bias and a bias pot for each power tube. Also being able to adjust bias settings gives you a bit of tone control at least on a scale of different IC's or cable. FWIW.
Its my understanding that 'matched' tubes don't necessarily wear evenly and at some point in time you will have the same problem of the tubes not being 'matched'. In an auto circuit you have no control, whereas when you can adjust each tube individually you can monitor and maintain a balance between the push and the pull tube(s).
Anyway thats how I understand it and it is why I prefer an amp which has manual bias and a bias pot for each power tube. Also being able to adjust bias settings gives you a bit of tone control at least on a scale of different IC's or cable. FWIW.