This circuit was found in a 1970 US publication. Transistors are still common and the circuit can be used as a PWM shield or pulse transmission modulator.
This circuit was found in Motorola documentation from the 1980s. PUTs are not common components...
This low distortion circuit was found in a 1964 Electronic Design. The transistor admits...
This circuit is based on an uncommon Texas component today, as found in an American 1980s...