This interesting circuit uses a sodion valve that we have already described in an article on the website. The circuit uses several batteries for power. The phone is of high impedance.
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...