New to tubes

I just got a Musical Fidelity X-pre preamp, which contains two tubes (KT-88's I think). How do tubes age? Will I hear a deteriation in sound? Or will this go so slow my ears will adapt to it, so I won't notice it? Or will they just quit working when there too old?
Basically: how do I know when it's time to change them?
Thanx in advance.
A pre-amp with KT-88's?! Are you sure about that? Those ain't no
preamp tubes my friend!

Usually when preamp tubes get old and weary you'll start to hear some
weird noises coming from your system in the form of pops, cracklin' and
scratchy kinds of sounds...I think they named a breakfast cereal after
failed preamp tubes didn't they? I think most of the small pre-amp
(6922, 12AX7, etc) tubes have a lifespan of between 5,000-10,000
hours depending on the tube and brand. You can also purchase a tube-
tester, or bring them to a friend with a tester, or service joint with one
and have'em tested out.

Wow Marco, I didn't mean to stress you out: three postings :). Not sure about the KT88's. Could it be EC 88's? Does the type of tube matter for the lifespan? Maybe a tubestester is a good idea, although I might be a little paranoid, since the tubes installed are about half a year old, and I even have the original ones (which were replaced for better sounding ones, according to the seller). Is a tubetester easy to get hold of? And how much would such a beast cost?
Nah, no stress here. Just a funky connection to the internet or bad browser. I cleaned up the mess before you replied (phew). It was hangin' up on me and I didn't think it posted after five minutes. Yeah, you have ECC88's which are the same as 6922's. Lifespan is rated at around 10,000 hours tops, depending on the pre. You know if that's the only piece of tube gear you own I wouldn't go the bucks for a tester (you can find them for anywhere from around $100-300 on average I'd guess). They are one of the more common and coveted tube-types, and also one of the most counterfitted as they can command a high price on the NOS market. Buy from a reputable seller. At 10,000 hours a pair of tubes is likely to last you 3-5 years of listening say 6-8 hours a day. So if you just make a note to replace them every three years, or when you start hearing the rice crispie dudes inside your rig, you can avoid the cost of a tester. If you want a tester they come up here and on may have to get the one you buy calibrated though. I use a BK707 and it serves me well. There are others that do an excellent job, but do make sure they test your tube type(s).

Thanx for the reply. May I bother you with another question, not about tubes this time? My poweramp is a real class A-device, and runs extremely hot. To the best of my knowledge, this should shorten the lifespan of the transistors (Sanken). I have the opportunity to buy a couple of them, but on the other hand, the amp is working (extremely) fine, so maybe I'm just wasting money, and I know zillions of ways to waste money in ways that will provide me with instant pleasures... Any input (not on instant pleasures though) would be appreciated.
Tube Pre and Class A ss power amp-I really like that idea .
Keep it simple change the tubes every 2 years,cost on 6922/EC88 minimal.I agree 5000 to 10000 hours life span.Try some different brands,fun to do.NOS is good but beware paying to much.I am using Siemens CCa's in my Pathos Logos,works nicely!
I'll second the Tube pre and SS amp! (AR LS2B Mk2 and 3 Threshold S-300's!) As far as tubes are concerned, have some fun. Each tube will have a different sound and it is kind of fun fooling around with them. I agree with Marco, find someone with a tube tester or get one for yourself.

You will find the prices will range from low to outrageous. Decide on a budget and start buying some. You can usually recoup most of your cash in the resale market, if you purchase wisely. This will allow you to try many different tubes.

Hop over to and talk with some of the tube guys over there, they can be a real help choosing. Welcome to tubes, it is quite and experience!
I think of changing tubes like changing oil. I do it regularly (once a year or so) whether they need it or not and certainly before they get 3,000 miles on 'em and get all black and sticky :)

Besides, it's fun to get a little bit different sound every year or so.

one thing not mentioned so far: diagnosing pre-amp tube problems is a pretty simple exercise, and you can do it without a tube tester. If you get bad noises (of any kind) in one channel only, turn off the pre, unplug it, switch the tubes from L to R, one set at a time (input, output - I'm assuming there are more than 2 tubes in your pre....) and see it the problem moves after you power up again - that isolates the problem so you can figure out which tube to replace.
Ok guys, thanx for your help. There's nothing deeply philosophical about my set-up though. I changed speakers, but they couldn't get along with my ss-amp, so first I bought this huge class A power-amp, using my old integrated as pre. When funds allowed (or actually, they didn't....) I bought a secondhand pre-amp, which contained tubes, and combined great, so I decided to keep it.
I guess, since there is plenty of life left in the tubes, I first upgrade the interconnect between pre- and power amp, and then I might have some fun with tubes.
Sorry I couldn't chime in again last night Satch. I went to bed with a hangover...not because of your questions though. That may explain all the additional copies of my post! Yes, I'd concur; tube pre with class A SS can be a nice combo when done right. Hang onto your tubes, save your pleasure money for the prostitutes and enjoy the music!

Marco, who said anything about prostitutes? I think my girlfriend wouldn't be to happy.... :)
And Musicslug, actually there are only two tubes in the pre, but I still can switch them, so your idea is valid. Although, with two tubes probably the same age, it would be easier just to replace them both I suppose. And TJ, since tubes ar more expensive then oil, I don't think I'll replace them that much, besides, I just got 'em, so I'm still rediscovering my music at the moment..
Just one other remark: first thing I'm going to change is the cheap, plastic offboard psu (12V/500 mA) for something homebuild and beefier: 12V/5A. I guess that will improve the pre a good deal.