Old SS amps

I have a Mark Levinson No.23 and a No.27.5 which I acquired used about twenty years ago. Although they have not in in use for several years now, I am confident that I can plug either one into my system and they will do just fine.

How long will a amplifier last if it's stored away in a box? Is there a shelf?

@emergingsoul 

The process by which electrolytic caps self-heal is suspended when not powered. Caps can become severely dried out as a result.

There is no hard expiration date, but any equipment that uses electrolytic caps (not just amps) and has been in storage for a long time should be brought back to life slowly and safely on a variac, as long as it has a linear power supply (SMPS-powered equipment is another story, but few audiophiles own any). The variac process allows caps to reform. Long-stored equipment should never be plugged straight into the wall.

A variac is a variable AC supply. It's quite inexpensive and well-worth buying if you plan on putting any long-stored gear back in service.

I have/use a Yamaha RX-Z9 bought new in 2003 now with over 35,000 hours that still functions like new.  Maybe the fan is a bit louder.

I love my carver stuff.the 500 is on ferris buler day off movie.i have nelon audio refresh them.epic and enjoy the music.he puts blue led in the meters and they think there mcintosh.

OP

20-year-old amps, as other have posted is just at its prime (as long as it is not abused). If it's a Pass, then it can be recapped if you wish at the factory.

I would grab that offer (if it's a Pass) right away assuming the price is right

My old amps were Rotel and one of the first Decware amps. these were about 20 years to this day, and they all sounded great, no need for CAP changes.