Design Life of Vintage TV sets

[compucat]

Looking over the restoration threads got me wondering just what was the intended service life of a typical 1940s or '50s TV set when they were being designed. These sets we have are 60 years old because previous owners never threw them out but by the time they get to us they have not seen power in at least 30 years or more. Manufacturers were always churning out new and better models and I have seen printed ads saying if you have a 10 inch set it is time to upgrade to a 12" or 17". Another ad said if your TV is more than two years old it is time to replace it. Does anyone know how long these sets were intended or expected to last when they left the factory?