Does a tube need the break-in hours?

Most probably not, but not sure why :) 
Does anybody know a good substitution for 12AT7WA tubes? I have bought 8 of them about 10
years ago for Manley Stingray. Now, when I need a replacement, none of them are good
(ones are labeled by Manley others are Philipps). 
(An almost 20 years old Stingrey remains in a good shape.) 
For any Amperex/Philips/Valvo tubes, the late 50's to mid 60's production are the very best.
thanks! then NOS tubes would be the most appropriate (though it should be almost impossible to consider a new tube or one in a good condition from 50s or 60s). 
I have hundreds of tubes from the 50's and 60's.  No problems.  Much better than most current production.
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.