Smash
Hack
That is great because I have NOS RFT in my amp now.This statement is only partially correct.
RFT EL34 from the 60's and 70's, Mullard EL34 from the 60's and 70's and RCA 6L6GC blackplate from the late 50's and 60's have an almost infinite lifespan.
I have measured these tube types after a reliably assured rehearsal & live use of a total of up to 3,000 hours with at least 70-80% residual power.