Found in old documentation, this circuit can be implemented even today with the use of a 2N2646 for the unijunction and a TIC106 for the SCR.
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...