Using the LM170 integrated circuit, this circuit was found in the May 1970 Radio Electronics magazine. The transistor is general-purpose, and the potentiometer adjusts the gain.
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...