Questions about retubing BAT VK-75SE

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?

Newbee,
I don't know what caused the cracks. I am just afraid it might have been damaged in some ways that I am not aware of. It probably means nothing other than making me feel better.

I ended up not using triples. Went with matched pairs, but use one pair on the left moost 6sn7 spot for the left channel, then the other matching on the left spot for the right channel, then the next matched pair in the 2 middle 6sn7 spots and so on...

I'm with newbee. If the 6sn7's are working...don't worry about the cracks...