How can you tell when tubes are shot?

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.