How long can preamp tubes last?

very specific to designer, the tubes, tube grading and the genius of the designer and the engineering culture of the firm. Roger Modjeski ( Music Reference ) and Gordon Gow ( good old Mac ) come to mind…soft start, tight regulation, a deep understanding of the published specs and adhering to operating envelope ( or knowing where to push or trade - Modjeski in particular a genius there…see Burning Amp for a taste ….. ( rca handbooks invaluable as a…starting point )…. tubes in preamps designed by above sometime see 10 k hours. i just replaced a set of 6H in a modern ARC w 4,730 hours….i test every year…
have fun…

i have a 1961 and 1965 mac 240 and 110 Z, all the records of work, tubes, performance clinics….the small signal Telefunkens have held up well. All due to engineering approach and philosophy….
oh ya, and they sound great…

have fun

rolling means changing the tube to another compatible type/brand/year of manufacture, etc…..it’s a wonderful sub cult. IF i were you, start a new thread with subject like: Tuberolling the Freja + ?
that will get ball rolling…better…

btw, the Schitt book is a good read.

+1 @tomic601  I've a set of 60s Telefunken Dynaco ECC83s I've been running since 1987 and they're still sounding wonderful.