This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
The circuit shown in figure uses a photodiode as a sensor element and its main feature is to have...
This version of the preamplifier is one of many that the reader will find on this website using the...
This interesting circuit was found in an English documentation. It generates sound similar to...