This conventional 4 channel circuit with the 4017 and 555 was found in the November 1991 Radio Electronics magazine. The potentiometer can be 47k and it controls the speed of the effect.
In the absence of a modulation signal, the carrier of this simple short-range transmitter is cut...
This circuit was obtained from an 80's Electronic Engineering. The circuit detects ice formation...
Other operational amplifiers series operatives, such as MC34072, MC34074, MC35071, MC35072,...