With tube preamps, tube replacement is not the problem: the above posters are correct about small-signal tubes, and I would add that the studies done in the 1950's all confirmed that longest life and best sound is achieved by keeping gear using small signal tubes turned on 24/7. Why? Most gear uses solid-state rectification, which is very hard on tubes when the unit is powered up. The thermal cycles they experience at power up and power down also beat them up over time. They pass little current in most preamp circuits. For these reasons, they are, generally speaking, best left on.
Tube preamps have other problems, specifically, noise, the inability to drive long interconnects without bass rolloff, and impedance mismatches with power amps, which also causes bass rolloff (I have written at length about these issues in other threads). However, only top-shelf solid-state preamps layer space and have the musicality of tube preamps. Thus, the conundrum.
A couple of suggestions: for solid-state, the Rowland Synergy IIi can be had for roughly $3k used and performs well; for tube, the basic VAC Renaissance preamp comes in around $3.5-$4k used - it uses output transformers that eliminate the problems of driving long cables and impedance mismatches with amps.
Good luck.
Tube preamps have other problems, specifically, noise, the inability to drive long interconnects without bass rolloff, and impedance mismatches with power amps, which also causes bass rolloff (I have written at length about these issues in other threads). However, only top-shelf solid-state preamps layer space and have the musicality of tube preamps. Thus, the conundrum.
A couple of suggestions: for solid-state, the Rowland Synergy IIi can be had for roughly $3k used and performs well; for tube, the basic VAC Renaissance preamp comes in around $3.5-$4k used - it uses output transformers that eliminate the problems of driving long cables and impedance mismatches with amps.
Good luck.