Choose and replace the right tubes
The lifespan of a tube principally depends on 3 factors: how much
it is used, its quality, and the hits it is given.
When you replace the tubes, especially the final tubes, they must
be "coupled" and we can see why in a simple example: the
final of a tube amp is like a scale that needs to even weights to
work good. The "weight" in question is the capacity of
amplification in every single tube, which can be completely different
even in tubes of the same brand. This is why to get our scale to
work well, the tubes need to be chosen among tens and tens and tested
at the tensions they will need to sustain.
you hear that your amp is "tired", with loosely basses
and from the overdrive "easy" and squeaky, write me, I
will tell you what to do.