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.
This circuit for loads up to 10 A was found in a 2005 Linear Technology documentation. The MOSFET...
In this circuit of a 1956 publication, the handset must be high-impedance magnetic and L1 has 200...
This circuit can be used to obtain a zener voltage from a common zener of another value, adjusting...