This rectangular signal generator was found in an Electronics World of 1966. The transistors are from that time and modern equivalents can be tested.
The sensor for this circuit, found in a 1992 publication, is a phototransistor. The power is...
This circuit can generate signals of frequencies up to 1 or 2 MHz, tuned in the capacitor. The...
Suggested by Philips documentation from 1968, this circuit uses components from the era that can...