This type of logic is no longer used today. The circuit is from an old American publication and the integrated circuit is uncommon today. Diodes are general-purpose tpes.
The figure shows three circuits for using headphones in amplifiers with speakers that do not have...
In this charger, the charging current is basically limited by the LEDs. The transformer is a low...
This configuration is from an old integrated circuit manual. The circuit can be applied to modern...