Although it depends on tube quality, VTL are more friendly in tube life. I quote the VTL750 v2.2 manual:
"Tube replacement need not be considered until after approximately 3000 hours of use (roughly 3 to 4 years depending on your listening requirements.) As the tubes age beyond their peak performance they begin to lose their ability to provide full power. This usually results in some loss of control in the bass and a general softening of the sound in the upper frequencies."
I had some 6550C SED tubes used in a pair of VTL MB450's approaching 4000 hours and they still tested perfectly in a transconductance dynamic meter.
That would be about a year for my friend who is retired and listens 8 hrs/day And he just got the latest (?) VTL 450 monoblocks and 7.5 preamp.