This circuit was obtained from the July 1970 issue of Radio Electronics magazine. Zeners are power types that can provide a good current to the circuit. Selection is made by rotary switch.
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...