Does a tube need the break-in hours?

Thanks guys, Mike and tomcy6 !! The tubes were kept properly, of course. And I bough them directly at Manley in Chinos, CA, about 15 years ago (they were not expensive at all). It did not clean the pins (legs), I though, since the problem is not permanent, this may not help. More importantly, i did not think that tubes may also fail because of some problem in the amp. I think now I have enough info to ask to Miss Eva Anna at Manley. Thanks again!
nodari

I just retubed.... and actually changed variety.    That said I think sometimes your brain, ears, and expectations can sometimes play tricks on you.  I had an older quad of Gold Lion KT 66 , with brand new speakers so it was a poor frame of reference to begin with.

I installed a quad of Mullard EL 34 and after letting it settle and checking the bias again I wasnt overwhelmed,   So i let it play and came back a little later and it sounds fantastic....  I think after an hour or so a tube amp is "ready" so to speak

We've sold vintage tubes on 'bay for a decade (tekdesinc) and also are designing high-end tube gear. There's 4 categories to this question:

1. raw new modern small signal tubes: definitely breakin for 100-200 hours depending on brand. If cryo'd halve the time. (cryo is a good idea BTW as the thermal exercise also linearizes the raw metal structure).

2.  raw new modern power tubes: this is difficult as you don't want to burn their limited lifespan so breakin for 50 hours until critical listening +/- 50% depending on brand. If cryo'd halve the time.

Next 2 are for vintage tubes as they are rarely unused, typically 95% are used and already 'broken in' per se.

3. vintage small signal tubes: since these have probably been sitting around,  breakin for 10-20 hours depending on brand. Sylvania, RCA, GE require 150-200% more time as they have commercial alloys. WECOs rarely need more than a couple of hours before listenability, but like wine they age nicely.

4.  vintage power tubes: again this is difficult as you don't want to burn their limited lifespan so breakin for and hour or two. Always warn power tubes an hour + before listening to avoid severe stress to the metallurgy.

When I swapped the stock 12AX7's in my preamp for Gold Lions, I would say the new tubes did sound slightly better after around 100 hours of use, but the difference was barely noticeable.  By "better", I'd say that acoustic sounds were very slightly "smoother".