Tube preamp reliability vs SS?

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
  

Yep,
AL makes a good and specific observation, my reply was more general in nature. My original  (early version) Coincident Line Stage had 18 db of the gain. My DAC has an output of 3.2 volts and my speakers  are 94 dB sensitivity. I had too much  gain, couldn't go past 10 o'clock on the volume control. I replaced it with a 10 dB gain version  from Coincident and all was well, VC  range  now is  11-2  o'clock for most recordings. Total system gain has to be taken in to account.