Tubes going bad???


Do tubes “go bad” slowly? If so, how do you detect when they’re “going bad”?

Some years ago I had a lesser tube system than I have today and was not so critical in my listening. As I recall, there came the point where I obviously needed to re-tube, my system sounded awful.

Moving forward, I’ve stepped up significantly in my equipment (Conrad Johnson’s Premier 16LS and Premier 12 mono’s)+ other tube gear. With consideration of the pursuit of system optimization (upgrades, tweaks, placement, etc.), how do I know if my tubes are performing optimally - sounding as good as it possibly can? If tubes do degrade slowly they may only be 97% today, 95% next month, 92% a month or so later at which time it becomes apparent it’s time to re-tube. If this is the case, I’ll have gone through a period of less than optimal tube performance that I did not catch on to until it became very apparent.

So, do tubes go bad instantly or is it a slower process that needs monitoring?
rbschauman
Unless a tube catastrophically goes bad, and you will know it when it happens, it's "normally" a somewhat slow process; the amp will begin to sound "sluggish" with a sense of loss of dynamics and general "oomph." Bass becomes less defined, with more boom than a pure note with texture. Depth of stage collapses as microdynamics and ambience are lost. Your words indicate that you care enough about this and my sense is that you will notice these things and hence will know when it's time. Power tubes go long before preamp tubes; rarely do I replace the preamp tubes due to loss of performance.
Simple and angst free method. Keep at least one set of spare tubes about. When you think your sound may be deteriorating insert the new tubes and see if there is a noticible difference (they should have about 24 hours to settle in). If you can't hear a meaningful difference pull them and go back to the old tubes.

FWIW I agree with Stevecham's comments.
I think the best way is what Newbee said, have a backup set.

I thought when I got my tube tester, that was all I needed. It does help with many things but I also found out that a tube "could" measure good and still sound not so good.

It's hard to notice the slow degradation and you are right, you may end up with many months of sub optimum performance.