This LM380-based circuit was found in documentation from the 1980s. The components are current, and the transistor may be a general-purpose equivalent. Note the use of a medium impedance speaker.
The sensor of this circuit can be any phototransistor and the SCR can be the TIC106. The circuit and...
This circuit consists of a controlled charge to discharge batteries under test. The circuit is...
This amplifier from 100 to 150mW was found in a Japanese documentation from 1967. The circuit uses...