Back in the day our electronic entertainment consisted of little more than a radio. The family gave no thought to what was inside until one of the tubes failed, prompting a visit to the local drug store with its tube tester and ready supply of replacements.
Then came hi-fi and an interesting thing happened. Because of the heat issue, relegated largely to the output stages of an amplifier, separates were born. The separate preamp driving an amp on a separate chassis was a popular way to go.
The divide, between separates and the integrated amplifier (or perhaps AVR), still exists today in both the 2-channel and home theater worlds. Long forgotten is its genesis, since with solid state electronics heat is no longer an issue.
Or is it?...