OK. I appreciate all your inputs, and will take note of them when I do ask for assistance.
Please note that in my first posts I just relayed my recent experience with circuits that did used to work perfectly, but now they don't. I also mentioned the fact that I was trying to figure out what was ...

The first circuit works fine (blinking LED, speed adjustable with the trimmer).
Added the second circuit, and that's where it gets flaky. First circuit? :?: Second circuit? :?:

Remember please that not everyone has seen those videos, or will make a special visit to YouTube on your behalf. Can you ...

OK. Next step in the - starting to be a never ending - story.
I built the clock circuit as per Ben's video instructions ( https://youtu.be/kRlSFm519Bo?si=mSM3vmfU6GLigqLs & following episodes) and it all worked just fine (I swapped the second and third NE555 by an NE556, but it all worked as ...

@BigDumbDinosaur
Thanks for the advice.
At the moment I am using an LS version, but that can easily be remedied. Just need to source the AC version.

Now that I'm retired and starting to feel nostalgic I dug up the cardboard box and am now in the process of restoring it...by the clock circuit of Ben Eater ...
I should caution you that Ben Eater’s videos will, at times, ignore design and/or construction details that are important in producing ...

For a bit of nostalgia, you could read his page about slide rules .

I've never owned a proper sliderule, I was intrigued by them though, and might pick one up in the (near) future.
I did own one of these addiators at the bottom of the page though (don't know where that got to, being a pack-rat I ...

All the (E)EPROMs I'm aware of are single-supply. EPROMs usually require a higher voltage to program them; but once they're programmed, operation in your circuit requires only 5V. Hopefully you'll find that to be a relief.

I meant to indicate I will replace the original 2708 - which needs +5 ...

@ Dr. Jefyll & BigDumbDinosaur thanks for your input.
I've started reading through the primer (and downloaded some referenced documents). A very comprehensive primer indeed. It highlighted some things I hadn't considered or thought of.
Made me reconsider my course of action(s). I guess I'm going to ...

I built mine when it appeared in the issues of Elektuur and after the books came out.
After some time I got married, moved and bought an ATARI ST. My Junior went in a cardboard box and into storage. Now that I'm retired and starting to feel nostalgic I dug up the cardboard box and am now in the ...