This circuit with its light source was found in American documentation two years 70. Or transformer of the type found in small transistor radios of the time. The transistors are general-purpose.
The figure shows how to implement an alarm buzzer in an LM3914 to warn about crossing the scale...
This circuit can act as a shield being controlled by a microcontroller by pin 1 or 2. The...
This circuit was obtained from a 1980's QST magazine. The circuit can generate 1 to 15 MHz signals...