How can you tell when tubes are shot?

I have an ARC REF1 and ARC REF Phono Preamp as well as assorted solid state gear. I leave everything on 24/7 and am wondering if the tubes just quit working (ie: get really noisy) or whether there is a gradual decline in their performance? ARC makes recommendations on who long they should last but I have been running the REF1 steady for over 18 months and haven't noticed anything.
It is a gradual decline. If you have run them 18 months 24x7 I would definately replace them. If anything you do not want to risk an all out tube failure in the preamp that could damage something. I will replace the ones in my LS-15 at least once a year if not a little sooner, and it is only on 8-10 hours a day. Good luck, I am sure you will be surpised at how much the sound has changed when you put the new ones in.
It depends on the tube and whether or not you are running both the plate and filament voltage. Most units have a standby, that keeps the tube warm, but not on. This can extend the tubes life quite a bit (assuming it's in standby 24/7 and on much less). It also depends on the tube, many NOS tubes can last much longer than current tubes. Mullards are noted for their long life (although I've found them to be a bit "tubey" sounding). Siemens are also long lasting and I really like them--very transparent sounding. If I remember correctly ARC charges a real premium for you to buy tubes from them, so I would recommend a different source. Upscale Audio, Tube world are two I've used with good results.
You may not notice the slow decline. You may be use to the sound. Since you will need new tube eventually, get some and see if it sounds better. If the same, just save the new tubes until later.
What Sugarbrie said. The sonic decline happens so slowly,
that we do get used to the sound..if new tubes are inserted,
and allowed to warm-up..there should be an obvious "ah-ha" the highs are back.,.. If not, the old
ones are still pretty good.
Is there such a thing as a tube tester? Thanks for the advice, I hadn't thought that a complete failure could cause damage. Duh. We don't want that so I will pry my wallet open and spring for new ones. I just hate to be wasteful. In my opinion the system has sounded better than ever. Plenty of highs, lows and everything in between.
I was advised to look between the pins and if there were dark spots between them then it was time to change out. I don't know how valid this info is, but I did have some Bugle Boys that sounded soft. I pulled them out turned them over and lo and behold dark spots between the pins. Go figure. Best of luck on your search.
When I was in the Air Force, I worked on a few systems on
B-52's that had tubes..and we had tube testors..but they
don't tell the whole story. A Ferrari and Porsche could
look almost identical on paper..or in Road & Track test
results...but still "feel" and drive very different from
a driver's perspective.... and an old tube could still look
to be good, when indeed it would sound poor, or two of
the same model tube from two different makers could both
measure the same..but sound very different...IE: trust your
when i need to know if a 9v battery is still good i touch my tongue to it. i'm guessing you could do the same to the tubes while they're in the amp. i'm going to test mine right now.

ignore previous post. ignore previous post.
Guess the girlfriend wasn't around Kubla?
Kubla must be an Army the Air Force we were so
macho...we used "other" body parts to test electical
voltages....let alone keep the curl in our hair!
I think there's allot of good advice on the previous posts.
I might add that turning the epuipment on/off really is not a problem with the newer design ARC epuipment. I got tired of replacing tubes so I just plan out listening time to turn
everything on about an hour before. Keeping the system on also creates one other gremlin and that is that resisters/capacitors begin to dry out over a long period of
sustained use which presents degradations apart from the
tube issue alone. I tend to buy the highest quality I can
afford and then keep/tweek for along time. As such, I believe it's best to turn the epuipment on/off if there are
sustained periods of non-use.
I like Sugarbrie's take which is an easy way to tell. Another thing to watch out for (if you are not used to switching/comparing tubes) is to allow them to cool all the way down before handling/changing them. Not doing so can damage or take a lot of life away from them (especially non Russian 6922 types many of which are very frail). Another good practice is to clean the glass globes and pins (I use electrician's alcohal which is cheap) and use a clean piece of cotten to handle and install the tubes which will keep skins oils and such off of them.
Hi Ntscdan; I keep my SF Line 2 in standby when not in use, and I found out the hard way when to replace it's tubes. After a year or so of use, the sound (music) becomes harder, brighter, more "brittle", and fatiquing-- but this happens gradually-- at least with the Sovtek 6922s. When I finally realized what was happening and replaced them with a new set, it was like having a new pre-amp. Now I replace them every 12 months or so. Cheers. Craig
Tube preamp or amp are not supposed to run 24 hours a day unless they have a stand-by feature.
Any recommendations on replacement tubes for the Audio Research PH3 phono preamp? Thanks in advance.
Thanks for all the great tube advice. The reason that I run my stuff all the time is that I actually get to listen to music from the time I get up until I hit the sack. Plus I use the record out on the REF 1 to feed an A/D convertor which feeds a great jazz station from Seattle (KPLU) through out the house. I have ordered replacement tubes from Audio Research because I guess I just feel more comfortable getting them from the folks that built the stuff, plus the little rings are cool. I do use a glove whenever I am handling tubes so as not to leave any marks, kinda like installing halogen bulbs.
Let us know how it sounds.