This circuit has tone control, and its power depends on the supply voltage. The circuit is from the Philips integrated circuits manual from 1990.
This shield circuit uses a common CMOS port. The voltage depends on the interfaced logic. The...
This circuit was published in Popular Electronics from the 90's. The components are common, as...
This circuit with SCR was found in an old documentation. The SCR can be the TIC106, and the...