This circuit is from a 70s documentation. The maximum sampling rate is 800 Hz. The operational amplifier is a common type at the time.
Found in a magazine 73 for radio amateurs, this circuit has two settings, one for the interval and the...
This good quality amplifier found in a 1982 documentation has a traditional complementary output...
A low frequency divider can be made using common unijunction transistors as shown by the figure...