This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent components. The transistors may be BC558 and the transformer is obtained from a disused transistor radio.
Two inverters, of the 6 available in a Low-power Schottky 74LS04, are used in this anti-ring...
Found in Radio Electronics from the 90's, this circuit can be implemented with other operational...
Taken from a 1956 Raytheon transistor manual, this circuit uses varistors to obtain modulation of a signal...