Suggested by a Popular Electronics from the 90s, this circuit triggers an external load, relay or recorder, when the telephone line receives a call, thus enabling its recording.
This short-range, medium-wave transmitter was found in a 1966 documentation. The transistors are...
This Hartley-type audio oscillator was obtained in an earlier 1973 publication. It can be...
This low-power benchtop circuit has an output for external use and other features. The circuit is from...