Tube preamp reliability vs SS?

You can listen before 30 minutes, you don't have to wait that long. The warm up time, optimal performance, for tube gear varies depending on manufacturer. Changing out a tube will not void a warranty. It is pull out the old and plug in the new, simple as that. Now on a tube amplifier it may NOT be as simple as that as biasing is required and how biasing is performed varies among manufacturers'. It can be quite simple to a royal pain but this isn't about tube amplifiers.

Tube life? well that depends on the circuit. Conrad Johnson gear about every 2-3 years in my past experience with their older gear. Their newer preamps  running 4 hours a day I would venture about the same but it will vary on the quality of the tube used. Chinese tubes don't last in my experience, even some of the premium ones at those premium prices although some sound quite good. The better tubes are from the golden age of tube manufacturer from the 1930's through  the 1970's. These would be tubes made in Germany, UK, Holland, Canada and USA. Also some of the Russian tubes are also quite rugged and will last longer. The older the tubes, generally the more expensive they will be. There are many reputable tube vendors to purchase tubes from as well as the manufacturer. A further word about tube preamplifiers, don't worry, be happy. They are as reliable as SS. I have been using tube pre-amplifiers exclusively for the past 30 years and have NEVER had any problem other than replacing tubes and an occasional fuse and I must say they are fun to own. You can try different tubes to suit your tastes but you don't have to.

Good advice and comments  given above.  The tubes  use in preamplifier are typically  low signal and often run conservatively, they can last year's if of good quality.I have a Quicksilver preamp that I  use in a 2nd system, it's 's 23 years old and hasn't  missed a beat since the day  I bought it new. You can tailor the sound via  trying different  tubes. Simple  modification like capacitors or better fuses make a difference as well ďue to the simple  circuits of most tube preamps. My advice, get one that the  builder provides a high quality and  robust power supply. Power supplies  matter.
Good luck,
Charles,

articdeth-

I like the combo of CJ pre-amp w/ a solid-state power amp.
What other gear, including cabling, is in your system?

Keep me posted & Happy Listening!

Very good advice given above.  It really depends on the tube type, the vintage/manufacturer of the tube, and the particular circuit design.  When tubes are driven close to their maximum rating, they don't last long, but driven modestly, the same tube might last for an extremely long time. There are people who claim that their tabletop radios are on almost all day and the tubes have never been changed in 60 years or more of operation.  

Within a given type, there are some tubes noted for their extremely long life.  These are typically vintage tubes.  I am certainly counting on these claims as I have invested quite a bit to get Telefunken ECC803S tubes for my phonostage (12AX7-type of tube); these have a reputation for being "lifetime" tubes.  I am also running some very expensive 348 and 349 tubes in my amp; the amp is rated for very low output (even for these tube types), so I am hoping that the tubes will last for many years.

A lot depends on the circuit the tubes are run in.  I know that some designers run tubes quite hard, like the old Counterpoint gear, and tubes had to be replaced every year.  

I would suggest buying a replacement set of tubes to have on hand at all times.  Once in a while, switch in the replacement tubes, if the sound improves dramatically, it is time to re-tube.

Excellent comments by the others. 

A concern I would have with both of the preamps you mentioned, especially if you are using digital sources, is their very high gain (specified as 20 db for the LD-2, and either 22 or 27 db for the CJ depending on what document is looked at).  If you are using a digital source, most of which provide non-adjustable maximum output levels of 2 volts or more, such high gains are very likely (depending on the gain of your power amp and the sensitivity of your speakers) to cause you to have to operate the volume control too close to the bottom of its range.

That is less likely to be an issue with vinyl sources, but depending on cartridge output and phono stage gain it could also be a problem in some cases.

Many other CJ line stages, btw, also have gains in the mid-20s.

Good luck.  Regards,
-- Al