If the battery is good, the LED flashes. This simple tester uses an LM3909 integrated circuit. We found this configuration in an old documentation.
This amplifier circuit is from a 1952 documentation. The frequency of the amplifier signal depends on...
This circuit was found in a Popular Electronics from the 90s. It is based on components still...
This 1975 documentation circuit must use a 6 to 9 V symmetrical source and the signal cables must...