Idea Box: QSOs With Very Simple Home Made Equipment ?

Making QSOs with modern manufactured equipment is fun, but what about doing it with home made equipment? (maybe not making your on components, such as capacitors, but using existing available components, and maybe sometimes modules. More fun ? I think so.
I have made my own direct conversion receiver for 80m, and later a simple VXO-transmitter for 40m. Making a few QSOs with that TX was absolutely fun. But what about making QSOs with fully home mad transmitter/receivers. Even more fun.

I have got the idea of trying to make at least one QSO on as many bands as possible, with homemade or at least modified surplus modules or equipment, as simple as possible.

On a few bands there are excellent simple options:

With ceramic resonators (CR) it should be possible to build relatively simple transmitters with the resonators "pulled" like it is done with crystals in VXOs, and then keying the buffers/amplifiers.
Many people have done this. As someone once said "a transmitter is 'just' an amplifier". Yes, but one of the stages is unstable, and oscillates ;)

But what about receivers ?
Direct conversion reception is often done with simple CW transmitter/receivers, but could it be even more simple ?

Today I was watching a video by VK3YE. He demonstrated a QSO made with a CR controlled transmitter on 40m (80m easily done, too, with CRs available). and here is the trick: He was using a simple regenerative receiver, set just above the point of oscillation. That makes it possible to listen to CW/SSB signals with a 3-transistor receiver (using an earphone). This is quite well known as well, but the regenerative receiver can be very critical and is considered a "two-hand" receiver. One hand on the tuning, the other on the regeneration control potmeter.
I consider this type of receiver as a direct conversion receiver with a self-oscillating mixer, although it is not classically considered as such.

VK3YE's trick was using a CR for controlling the frequency of the regen-receiver. The result is a far less critical regeneration control, and a far better frequency stability. How about a receiver with no coils to wind? Here it is.

On one of his videos he demonstrated a DX QSO with a CR controlled 30W TX and the above mentioned RX.
Doing this does mean that it is necessary to go "back in time" and use separate frequency tuning for the TX and RX, and having a "spot" function, so the TX frequency (just the oscillator) can be heard in the receiver.

No, I would **not** build such a set with vacuum tubes, though I know that it is quite possible. I do not like high voltages.

So many ideas, so little time, but it is a tempting project to try out after a few other things I would like to finish. Beginning projects is a lot easier than finishing ;)