Finally, somebody made a video about CMOS vs TTL logic chips and fake Chinese chips.

https://www.youtube.com/watch?v=Knfv...el%27sRetroLab

So, if you build a Sixty-Clone: DON'T BUY ANYTHING FROM CHINA! Get your chips from an official distributor such as Digikey, Mouser or Avnet.

Make sure you use the correct logic ICs and these are 74LS or 74HCT
See:
https://www.allaboutcircuits.com/tex...oltage-levels/

https://www.onsemi.com/pub/Collateral/AN-368.pdf