Regarding the life of 6c45pi tubes.
I haven't gotten to the point where one dies but I have had a couple get noisy. I'm guessing it was well over 1500 hours (maybe twice that).
I suggest polishing the pins.
A number of Russian tubes don't have the best pin construction and they get kinda dull sounding after a while. The noise floor will also rise.
I take some metal polish paste (my fav is Mothers Aluminum and Mag polish), put it on a half q-tip and put it in my Dremel tool. I slowly work my way around the pins, then clean it off and put a tiny bit of Caig Pro Gold on them.
Sometimes I'm positively shocked how much of a difference it makes to tubes I haven't treated this way before.
Think of it as a poor mans gold pins.