The MP1 is among the top 4 of my list. What's the life of various tubes in MP1, number of tubes/ models, and how expensive they're? Does certain tubes have to be replaced in set?
@hitsofmisses None of the tubes are stressed so they last a long time. The linestage and output of the phono section will easily go 10,000 hours.
The 12AT7s in the phono section front end do have to be quiet, but these are the tubes nearest the rear panel; the front and middle phono tubes do not have the same noise requirement. When the front end tubes get too noisy for that service, they can run fine later in the circuit. We've seen preamps in the field for 20 years that still have good tubes in them (with the customer claiming the preamp was in constant use; whether that is true or not is a different story...).