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 the circuit of a sensitive voltmeter using a difficult-to-obtain 5 uA full-scale...
The circuit is from the United States Hands-On Electronics magazine, February 1987 edition. The...
The circuit shown was suggested by Analog Devices (www.analog.com) in its Application Note AN-411...