This circuit was found in February 1976, Radio Electronics magazine. The components are from the time and are based on the 555. The power supply must be provided with the indicated voltages.
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...