KT88 vs 6550 tubes

I recently got a quad of EAT kt88 tubes for my Mcintosh MC275. Those are supposedly revered as one of the best. However, less than 10 hours one of them had a spark of fireworks in it and shorted the fuse. I heard KT88s are in general not as reliable as 6550. Is this true? 

I thought also that KT88 and 6550 are interchangeable in the MC275 without any additional bias adjustment. The original 6550 tubes in it has been working for a long time without issue.