Carver and Tube Life

I’ve been looking at Bob Carver’s statement tube amps, the Siver Seven 700’s.  These massive tube amps designed by Bob  have been around for years and the latest version of his 700’s can now accommodate KT120 output tubes and his best output transformer design.

EACH mono block uses 20 KT120’s! That’s 40 KT120’s total when it comes time to ‘re-tube.’  However, according to his description these KT120’s should easily last “50 Years”.  Is that truly possible???  Can the output tubes really last that long ?