This circuit was found in 1980s Radio Electronics. The circuit includes the power supply. The ICL8038 circuit was very common at the time in this type of application.
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....
This filter was found in Texas Instruments documentation from the 1980s. The circuit uses a common...
16 commercial test circuit for tubes and transistors appeared in Radio Electronics magazine in...