This circuit is from a 1965 Electronic Design. The transistors may be general purpose and the power supply must be symmetrical.
We found this circuit in a Popular Electronics of the 90s. Its purpose is to detect when it locks...
This circuit controls the passage of the signal from one speaker to another. The potentiometers must be of...
Obtained from a 1969 documentation, this circuit can operate at frequencies up to 500 Hz, counting up...