Can the sound of SS amp deteriorate over time??

Yes, electrical products can and do shift operating parameters over an extended period of time, especially if tempurature swings are involved. Sometimes, a simple alignment is all that is needed, sometimes parts need to be replaced and then an alignment will solve the problems. It all depends on the original design, how well that design was implimented, the environment of the gear ( in terms of ventilation and exposure to dust / airborne debris ) and the operating patterns that it has to deal with.

I get some units that come into work after 30 years that work and look like new. I get some other units that are two years old and look / work like they should be put out of their misery. As such, even a poor design can last a long time if it is babied and a robust unit can be falling apart if thoroughly abused. Most units are somewhere in the middle and therefore don't need a lot in order to bring them back into spec. That's why companies like Bryston can give the warranties that they do. Sean
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Short of bench testing an amp to determine if it meets spec, there is no way to tell for sure. Many, who consider measurements verboten, foolishly waste time & $ with ZERO improvement.

I've left my modified Adcom on for 15+ years and I've heard no deteriation in the sound.As someone said the design and how well you take care of your equipment comes into play. I also feel that providing your SS equipment with purified electricity provided by a good AC line conditioner and good power chords can't hurt.

Porziob: Thanks for clearing that up for me. I, my annnually calibrated test equipment ( HP spectrum analyzer, tracking generator, AF & RF signal generators, Tek scopes, etc... )and the experiences of the mass majority of my customers must all be mistaken. I guess that i'll have to start denying the differences that the customers experience and what i can measure, based on your above testimony.

Qdrone: It is my personal belief that leaving equipment on causes less stress than power cycling it up and down on a regular basis. That is, so long as their is more than adequate ventilation for such and "dust bunnies" that can accumulate both on and in the gear are addressed on a somewhat regular basis. Not only that, but i think that most gear sounds better too. Obviously, this is just my personal opinion, so take it for what it is worth. Sean
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Sean...In the field of ballistic missile guidance systems (lots of very complex and precise solid state electronics) we have rather extensive experience with continuous operation and with on/off operation. (The Air Force operates continuously while the Navy operates on/off). Navy systems are commonly deployed without problems for six to ten years, whereas Air Force systems last a much shorter time (which I can't tell). Believe me, the Navy has also looked very closely at possible accuracy benefits of continuous operation, and it is not significant. However, it is important that the Navy systems opearate in a "Dormant" mode when "off", where heaters distributed throughout the system maintain temperatures very close to those that exist during operation.