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.
The transistors of this circuit found in an English 1980s documentation may be the modern BC548...
This circuit causes an incandescent lamp to flash according to the input audio signal. The SCR...
This circuit was found in the 1990 Motorola Linear Databook and can use almost any operational...