Radio with amplifier (CB20486E)

We found this circuit in a publication of 1991. The audio amplifier is an operational that admits equivalent.

TTL Logic Tester (CB23671E)
We found this configuration in a technical documentation from 1974. It can test both TTL logic...
Rocket Altimeter (CB25357E)
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....
Twilight Switch (CB16588E)
This circuit activates an incandescent lamp (it cannot be of another type) when it gets dark. The...