This wired intercom circuit was found in an English publication from the 80's. The integrated circuit can be replaced by an equivalent, just like the transistor which is a general-purpose type.
This circuit generates a 1 MHz signal for general equipment calibration. The circuit is from an...
This simple preamplifier presents a high input impedance and can be used with microphones, piezo...
This circuit for the two-meter band of radio amateurs was found in 1980s documentation....