Listening for tube degradation

great thread that I don't want to lose track of, hence my posting, thanks all!

This is a very informative & great thread as Karelfd mentioned above. I also have to agree with Swampwalker that just because a tube exhibits microphonics does not indicate the tube is worn out. I have purchased brand new tubes that are microphonic in some circuits but are not microphonic in others. The use of tube dampers can greatly reduce or eliminate microphonics in most cases. I think I'm a little paranoid over purchasing gear that uses too many tubes and for that reason prefer a more simpler design.

If you don't have a tube tester the only other thing you can do is watch out for a sudden deteriation in sound or a drop in gain. I have had tube preamps where the gain suddenly drops and the tubes cease to function period with no harm and they sounded very good up to that point. I would think that one would want to exercise more caution here in regards to tube life with tube power amps since the sudden death of a worn out tube could cause circuit damage or in worst case scenario a small fire. So as mentioned above it is always prudent to have a spare set of tubes on hand. I don't know why most manufacturers of tube power amps don't include a electronic metering device that lets you know the amount of hours you have put on a new set of tubes.

i have noticed an increase in treble energy just before a tube dies. i have also experienced a crackling sound that can very load just before an amplifier output tube dies. it always pops a fuse, rather than damging my vtl deluxe 120. once i experienced a failure of 2 12ax7 tubes on my mac 275.
there was no warning sound prior to the tube failure. here again, a fuse was blown and i was able to determine which tubes needeed replacement.

Hi Pryso,

I don't mean to suggest that a tube tester, particularly one that can be obtained cheaply, is not a worthy investment. Certainly for my friend, finding out that a rectifier he had not ever used was shorted was very useful information.

My only caveat has to do with relying on data, even useful data such as transconductance, to try to ascertain how the tube will sound. I have current production Electro Harmonix 6sn7s that test spectacularly high in terms of transconductance, that sound like crap compared to near dead Tungsol roundplates.

I agree that combining measurements from a tester with experience IS very helpful. I merely intended to reduce the expectation that a tester will be a quick and easy way to select the right tubes for an amp and an easy way to estimate when a tube should be replaced.