amplifier longevity

There are Sugden A21's still going strong over 30 years later, so much for the Bogus heat issue.....

Depends where the heat goes. If the chassis is built to isolate other components from the heat, no problem. 

My Sansui 7070 receiver that is ss has been running in my wife's salon for over 25 years never shut off (except power outages). It still works like a champ. This was purchased new in 1978. I think it was the quality of components the used. These old receivers were way over engineered and when said and done were great value. 

The only piece of electronics I ever had fail was a HK receiver. No other amp, SS or tube,

I built my Hafler 500 at my desk in my shop in 1974.  Recent trip to my engineer showed it slightly out of bias.  Other than that, measured as if brand new and still sounds great on my Maggies (bottom end).

Cheers!