It depends on the preamp, some of them are tougher on tubes than others so you really can’t get a definitive answer. You can install new tubes from the same date batch for each channel and one will give it up after 6 months while the other can stay strong for five years. Happened to me a lot over 25 years with the tube-eating CAT SL-1
What I do is every two years is substitute a new set and if I don’t hear a difference I put the old ones back. This way I don’t have to stress over whether the tubes have lost something that I can’t hear because of the gradual deterioration nature of tubes. Other than that, when you hear hissing, pops or crackles, obviously then it’s time for a new tube.
What I do is every two years is substitute a new set and if I don’t hear a difference I put the old ones back. This way I don’t have to stress over whether the tubes have lost something that I can’t hear because of the gradual deterioration nature of tubes. Other than that, when you hear hissing, pops or crackles, obviously then it’s time for a new tube.