The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
March 2017 - Texas Instruments LM5166 Synchronized Buck Converters are available at Mouser for 3V...
This ouput push-pull stage using bipolar transistors was found in a publication of the year 1968....
This circuit was originally designed to automatically turn on a television when a video game is...