We found this circuit in documentation from the 90s. Instead of a voltmeter, you can use the voltage scale of a multimeter. The circuit tests batteries under load.
This circuit uses a 100 kHz crystal, but nearby frequencies can be obtained with appropriate...
This one transistor stage for audio signals was found in an old publication of the year 1958. The...
This is the typical audio amplifier for a 1967 television. We found it in a magazine from the...