This circuit was found in 1967 Philips documentation. It uses transistors from that time. Transistors can be replaced with modern equivalents.
This circuit produces a square wave signal with the frequency determinated by R1 and C1. The upper limit...
The FET can be a BF245, and the other transistors can be the BC548 and BC558 in this simple AM...
In this circuit, from a 1977 publication, we have the traditional version of a filter tuned to 1...