I have VPAs, but they are on dealer loan, so I can not really speak about reliability issues from my expirience. However, a close friend of mine is running VPAs for more than 2 years now, first with chinese tubes, and now with KR tubes and only once had a tube failure (the KR one) which was replaced by Nagra for free. Apart from that tube - no issues.
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