We found this circuit in a 1976 documentation. The FET can be BF245 or MPF102 and the power supply need not be symmetrical. The FET in the feedback acts as an automatic gain control.
When the input of this circuit goes to high level, the LEDs start to flash alternately. The...
This circuit already uses an integrated circuit from the time. Note the different encapsulation of the...
This power charger was found in a 1990s issue of Popular Electronics. Integrated circuits must be...