Does a tube need the break-in hours?

niodari,  unless your old tubes were exposed to extreme conditions like very hot and cold temperatures, they should be OK.  Fifteen years is not much to a tube.  Tubes from the 40s still work fine.  You may need to have your Stingray checked out.  It may be the problem.

I’m having trouble understanding your question . If you have multiple failures with new Tubes that have been stored , it sounds like your amp needs service . Some of the newer  Manley’s have changed Tube values due to Tube availability . While power tubes take 100-200 hours to break in , input/driver Tubes also require some time.  Usually less . If your tube pins ( legs ) are oxidized , clean them with De-oxit and a Q-tip . Also contact Manley directly and you will get a more knowledgeable response . Also IMHO NOS Telefunkens are some of the best Tubes on the planet . Unfortunately, their price reflects this .  But I would definitely contact Miss Eva at Manley . Happy Listening , Mike. 

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.