This circuit is from a 1975 RCA tube manual. It appears elsewhere on the site. R5 depends on the voltage of the amplifier with which it is used and can be changed.
This circuit that imitates the sound of the cowboys' calls with their “louder” was found in a...
We found this circuit loader in a French magazine Electronique Radio Plans from July 1993. The...
We have in the figure a traditional amplifier configuration with operational amplifier. The source...