Found in RCA documentation from the 90s, this bass and treble control uses an operational amplifier from the time that can still be found today.
To use the instrument for AC measurement, the tips are A and B. For CC use tips A or B for...
The interesting circuit shown in the figure, can have its gain digitally controlled and present two...
This simple MW radio was found in a 1975 publication, but it can be mounted with BC548...