This plug-in control was found in General Electric documentation from the 1970s. The SCR can be the TIC106 mounted on a heatsink. The circuit can be changed to the 220 V network.
This circuit was found in a 1992 publication, using an operational amplifier not very common...
This is a amplifier for XTAL high impedance earphones or piezoelectric types. Current drain is...
This circuit is from the LM111 manual of the 1980s. The component no longer exists, but...