This circuit is from a 1980's documentation for telecommunications. The circuit is used in SSB and the diodes must be suitable types for the application. The audio input is low impedance.
This sensitive touch key appears on this website from other sources. This version was taken from a...
This nonlinear gain circuit was found in a 1965 Electronic Design. The configuration can be used...
CMOS 4046 (PLL) is not very common. In this circuit it generates short pulses to excite a high...