Hey I was going to buy this
http://chicago.craigslist.org/nch/sys/2158040403.html what causes a blurry tube and can I stick that motherboard into a classic and have it work?
If the screen is bright, has good contrast but is blurry, it generally means that there is either a simple focus problem, or the brightness is simply cranked up too high. If the blurriness is actually jitter, that's often a symptom of capacitor-related problems, or loose connections. Both of these problems are common ailments in these compacts.
If the crt is dim and blurry, it could simply be worn out. The only practical fix is replacement of the crt itself. All compact Macs are good crt donors. To be safe, keep the yoke with the SE/30 and swap only the crt itself.
As Bunsen notes, you can put the SE/30's logic board into an SE with little trouble. However, you will not be able to put it into any other compact Mac without major work.