[bewilderbeast]

The heatsink cools the LM7805 power regulator, not the CPU. In the original 48k Spectrum, the heatsink was internal.

[nickt]

And if you use a modern switch-mode replacement, you don’t need a heat sink at all.

I know some folks like to put small heat sinks on the ULA though.

[SomeoneFromCA]

Soviet clones had ULAs built from individual 74xx ics. No need for heatsinks!

[nickt]

Excellent! I need to mess around with them at some point.