Comment by reader9274
7 hours ago
I built one from discrete transistors in a lab class in college, on a breadboard. Fun times debugging and getting it to work. Then I flashed an led with it right next to another led flashed from a 555 chip. With the same discrete timer caps, the flashing frequencies were different due to the extra parasitics in the breadboard discrete 555 version. So had to compensate the caps to make the flashes match each other's frequency.
That's a great exercise. The hard part is always that in chips you can pull stuff that is rather tricky discretely, for instance, a multi-emitter transistor. So you can't always do a 1:1 conversion but for a 555 it is still doable.
I saw this a while ago:
https://www.instructables.com/Designing-a-555-Timer-on-Discr...
Only because odd components aren't marketable. There used to be 4-terminal MOSFETs, they weren't sold after ICs became normal. Never heard of a multi emitter transistor being sold discretely but it's possible.
Dual gate mosfets were a godsend when building RF/IF mixers or preamps. Luckily I have a small stash as they're almost unobtanium and costly these days, but for most uses such as mixers and preamps they can be swapped with a pair or normal jfets in a cascode configuration like this one: https://i.stack.imgur.com/6Nyhg.gif
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I use dual gate FETs frequently for all kinds of tricks and they're super useful.
Is that what you had in mind?
Do you still have a video saved somewhere?