This circuit from a Popular Electronics from the 90's can generate signals from 0.03 Hz to 3 kHz depending on the value of the capacitor and resistor.
This circuit is one of many that the reader can find in this section for testing crystals. The...
The two integrated circuits used in this configuration can still be found. The frequencies of the...
This circuit was found in an American book on transistors from the 60's. The transistors are...