This circuit doubles the frequency of a rectangular signal applied to its input. The circuit has a 30 kHz input to obtain 60 kHz signals. We found it in a 1964 Electronic Design.
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...