This circuit is one of many that the reader can find in this section for testing crystals. The circuit uses an indicator LED. Transistor Q1 determines the maximum crystal frequency that can be tested.
The operational amplifier of this circuit is not very common today, because we removed the circuit...
This circuit transmits signals to an FM receiver placed at a distance of up to 200 m. The antenna...
We found this circuit in an American documentation from 1964, but it can be easily assembled...