What to give an adult lover of circuitry?

Question

Circuit design

I want to return my dad's former love for circuitry, soldering and creation in general. In the past, he worked as an inventor / designer / circuit engineer at various factories and enterprises. And he was very passionate about it. But now he rarely picks up a soldering iron and integrated circuits, except to fix something from the household.
Now he is very ill, and I am sure that the motivation of creation will give him additional strength to fight. What modern gift can be given to him in order to regain interest in such activities?
Raspberry Pi and Arduino, in my opinion, are more about programming and connecting different devices. And here I want more hardcore (not childish) circuit work.
Thank you!

Answer 1

Not cheap, of course, but in the subject
. And in general - the Internet is full of sellers of kits for assembling amplifiers and clocks on gas-discharge indicators, the entire aliexpress is packed with Chinese kits for soldering anything (clocks, home automation, etc.)

Answer 2

It depends on what dad did at work and what interests him.
If you are interested in audio equipment, then try to assemble a High-End class tube amplifier. There is a purely live circuitry (carry the ground wire around the case, and solder it in the place where the sound will be better.)
If dad is a radio electronics engineer, then he may be interested in assembling his HF radio station and joining the thinning ranks of radio amateurs - knocking Morse code with a key. The scheme can be found in the old magazines "Radio", the article "I'm building a new HF radio station". (Yes, it will need to be registered.)
If dad was engaged in power electronics, you can offer to assemble welding machines. They can also be sold.