This balance control for the channels of a stereo system was found in a 1969 Mullard documentation. The transistors may be the modern BC548 equivalents.
This is a typical RF oscillator configuration found in a 1980s documentation. The frequency...
We found this circuit in factory documentation from the 70s. The operational amplifier is from...
Found in 90's Electronic Engineering this circuit can be used to measure phase angles between two...