The original-technology standard-power TTL chips it's partly-built from are power hogs and run hot. The chip technology was making progress in leaps and bounds when it was designed, and it also contains a few later lower-heat "LS" TTL chips. One way to reduce the heat a bit is to run it from a regulated 8-Volt external DC supply. This will reduce the power dissipated by the voltage-regulator chip. Won't reduce the heat from any other part inside, but it's the only measure I know to take.
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