This circuit is from an old American publication. It divides a 40 to 60 MHz TTL signal by integer values such as 2, 3 or 4. The circuit must be powered by 5 V.
Also suitable for use as a noisy alarm, this Morse Code or telegraph practice oscillator was found...
We found this filter in documentation from the 1980s. The operational amplifier used is uncommon...
This sequential tone generator circuit was found in the July 1980 issue of Radio Electronics...