This is a commercial circuit from the year 1958. Transistors are germanium types and transformers and coils are hard to fild today. The circuit is destinated to the reception of medium wave stations.
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...