There have certainly been changes to the technology, but no where near as extreme as in other components, like CD players (dah, obviously, sorry about that no brainer). How long should an amp last? That is a tough question, a well made amp should last an awefully long time, decades. The capacitors and some other items may need to ultimately be replaced, but they should keep on ticking.
It is not unusually to see very old tubes amps still working and being sold. With your 18 Y/O amp, if you love everything about it, I would consider having it serviced and some of the components replaced (caps, etc. . .). There is no reason that it shouldn't still be a very good performer.
It is not unusually to see very old tubes amps still working and being sold. With your 18 Y/O amp, if you love everything about it, I would consider having it serviced and some of the components replaced (caps, etc. . .). There is no reason that it shouldn't still be a very good performer.