This circuit with transistors of the time was found in the November 1972 Radio Electronics magazine. The circuit also generates a sawtooth signal for use on an oscilloscope.
We found this circuit in a 1990 documentation. The operational amplifiers are type 741 and the LED is...
We found this circuit on an Elektor from the 90s. The frequency is given by capacitor C1. The...
Found in National Semiconductor publication from the 1980s. This gain-100 circuit can be...