Tube preamplifier lifespan

Yeah I think that what PS Audio said to you is a little misleading. 

It would depend on the quality of the product. But I even have a couple Dynaco preamps that I can personally date back to the 70's that I can plug in & they work. I'm sure some parts are out of spec though. 

I have an Assemblage preamp which is on offshoot from Sonic Frontiers built in like '98. It was modded to the gills with top of the line resistors & overkill pricey Hexfred diodes..the power supply electrolytics were replaced with Films in the original  build. I still use it occasionally & it sounds nice. I do get an audible scratch from the  Nobles volume pot when I pass the 12 o'clock position. 

So I think it depends on the product. 20 years is probably time for some electrolytic replacements but many old tube products are still alive & kicking. Well I did have a tube preamp manufactured in 2012 with a very small chassis that I had to replace the electrolytics after 11 years. Couple bulging caps but just replaced them all. 

gmcleod-

I'm quoting the OP's remark.

I still use a McIntosh C20 stereo vacuum tube preamp from the late ‘50s in my office.  First Mac pre with a glass faceplate and the last with a vacuum tube rectifier.  It’s still 100% original:  tubes, caps, incandescent bulbs.  Never needed to clean the potentiometers.  Those original Telefunken 12AX7s and 12AU7s are approaching 70 years old!  As is the vacuum tube rectifier with its soft start which probably contributes to the continued life of the capacitors.  That, and everything in there is run at a very sane B+ rail.  It still sounds great though admittedly highly colored in a very tubular way 😆. 

I wouldn't trust the opinion of someone who sells new gear about how long it lasts. 

I currently use a 20+ year old Conrad Johnson LS17 tube preamp. I actually spoke to a tech at CJ and asked them this exact question thinking I might need to have it looked over and possibly change some aging parts like caps in the power supply.

His answer, was, other than tubes that obviously need replacement as needed, my preamp, if I perceive it to be functioning well, is just fine.

The CJ LS17 runs 4 6dj8 (6922) type tubes which are likely not as heat generating as other tubes. Also I always have tube savers between my tubes and the tube sockets on the circuit board to keep the pins in the sockets pristine and keep the heat from the tubes a bit removed from the circuit board. I do this with all my tubes in my power amps as well.