Yes you can, sort of. I have an overhauled TV12 tester and have been experimenting with how tubes behave as they wear. I measure new ones and then periodically check them as they are being used in various gear and data log everything for each individual tube.
In my experience, little 9 pin tubes like 12AX7, 12AU7, etc., will lose transconductance (gain) as they age. However, the big power tubes like 6550 or KT66 or even EL34 will tend to high leakage as they wear - in other words, they actually fail from high leakage rather than loss of gain. So which mechanism dominates depends on the type of tube, but the rate of wear will depend on the circuit in which they are used.
Between my system which uses 16 tubes, and my local buddies which have tube-based systems, it seems that low-gain tubes don't sound bad at all so they effectively last a long time. But this doesn't apply to the power tubes which noticeably degrade after a year or two of use but still test fine gain-wise.
Arthur
In my experience, little 9 pin tubes like 12AX7, 12AU7, etc., will lose transconductance (gain) as they age. However, the big power tubes like 6550 or KT66 or even EL34 will tend to high leakage as they wear - in other words, they actually fail from high leakage rather than loss of gain. So which mechanism dominates depends on the type of tube, but the rate of wear will depend on the circuit in which they are used.
Between my system which uses 16 tubes, and my local buddies which have tube-based systems, it seems that low-gain tubes don't sound bad at all so they effectively last a long time. But this doesn't apply to the power tubes which noticeably degrade after a year or two of use but still test fine gain-wise.
Arthur