Lifespan of a quality solid state amplifier?

McIntosh for example seem to last forever. Most people feel an amp that are 10 years old are getting ready to retire but ss McIntosh amps from the 1960's like the MC-2100 still show up on this site regularly. That's always been a curiosity to me, is the McIntosh infinitely better than my Krell KST 100. I've recapped it once but are the transistors and other components that much better that they can survive decades longer? Is it the autoformer that makes them last. I would like an amp that lasts and I'm willing to trade off sound quality to achieve that. Some people are critical of the McIntosh sound but no one says they don't last forever.

Background noise like a hum is the biggest sign caps might need replacing. If the amp hasn't been used in awhile you should bring the voltage up gradually with a Variac. If you just plug it in after a long time it can cause a failure of the capacitors.