Questions about retubing BAT VK-75SE

yes, they do. However, you can change the sound slightly with new 6sn7's and the tube next to the 6h30s'. I used RCA 6sn7's and it's softens and sweetens the hights somewhat.

Matching is important on the 6sn7's, as the are part of a balanced gain stage...matched triples for each side.

Jfrech,
I also posted on AA and V.K. replied that the input and driver tubes should last longer than the output tubes and don't need to be replaced at the same time. But I just noticed that two of the 6SN7s had developed cracks at the base so I am going to replace them anyway. But finding matched pair is difficult enough; I don't know where I can find matched triples. Do you know know of any good source?

What is it about cracks in the base that you feel make it necessary to replace the tubes? I assume the tubes still have intact pins and hold vacumn. If that is so is there another reason?