Pre-amp tubes will last 5000 to 10,000 hours with 6dj8's outlasting 12ax7's generally speaking. Tubes being biased too high will burn them out faster-extremely high bias will have the tubes burning bright blue inside.
And yes, better tubes will last much longer as well as sound better. Telefunkens will give you the most life and best sound while I would avoid bothering with cheap russian or chinese tubes in such a nice unit (there are good russian and chinese also).
And yes, better tubes will last much longer as well as sound better. Telefunkens will give you the most life and best sound while I would avoid bothering with cheap russian or chinese tubes in such a nice unit (there are good russian and chinese also).