This detector was found in an old Electronic Design using transistors of the time. The circuit can be made with modern equivalent transistors. See the charts with your performance.
Based on TTL logic this circuit can vary both the frequency and the pulse width of a rectangular signal....
This circuit was found in a Popular Electronics from the 90's. It can be implemented with...
This circuit was found in a Hands On Electronics from the 90s. It is intended to supply old tape...