Add me to the list of those who can hear differences between tubes and who enjoy fine tuning the sound of their systems with old stock tubes.
aol, Talk to Kevin Deal at Upscale Audio. He is the importer of PrimaLuna amps and the expert on them. He also has a great selection of NOS and current production tubes that are priced from very reasonable on up.
He can probably tell you if there is a possibility that the tubes that went bad on you were not right for your preamp or if you just got some bad tubes, as you suspect.
Before you talk with him give the stock tubes a good listen and decide what kind of change in sound you want to hear with a change of tubes. He will give you his honest opinion, even if it’s not what you want to hear, which causes people to rant about him on this forum from time to time.
Buying old stock tubes does have risk. You can minimize the risk by buying from an established seller with a good reputation. Don’t let your bad experience sour you on tubes. They can definitely improve the sound of your system, IMHO.
Here are some other good sellers:
Tubemonger
Vintage Tube Services
Jim McShane
Brent Jessee