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.
The figure shows how to obtain a locking relay for an alarm circuit with sensors in series and in...
Found in Popular Electronics from 1969, this circuit uses a neon lamp from the time that had...
This is a simple rheostat circuit for motor control that works with voltages from 6 to 12 V. The...