This harmonic oscillator controlled by crystal was found in an American documentation of the 90's. The circuit uses transistors of the time. Current equivalents can be used.
We found this circuit in a publication of 1990. With the changes it can be mounted easily today....
This simple photometer was found in a 1977 Radio Shack manual. The sensor is a photocell, which can...
This circuit is used to test a triac and also to teach how it works. The load is an incandescent...