This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
I found this circuit in a 1980 documentation, but it can be easily assembled with BC548...
We found this alarm in an English publication from 1978. Although the original power supply is 3...
Found in old documentation, this circuit can use modern equivalent components. The signal has good...