I can't speak to reliability issues of Nagra, but I've also experienced KR 845 tube failure after only aprox. 100 hours on my Art Audio Carissa Signature. Now use TJ Fullmusic.
Reliability issue - Nagra VPA power not KR tube
I have a pair of Nagra VPA Type I on evaluation. I ran over the weekend. The chassis heated up to well over finger warm. Tubes are obviously very hot - 535 F. My friend that has had a pair for 4 years recently had a major issuethat costed him $ 2,000 to repair. As part of my evalution, I am curios to hear from other VPA owners, what reliability issues they have had and the costs to repair them. Are these amps one should avoid from a reliability point of view. Thanks