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.
Found in an 1868 Mullard documentation this circuit has a dynamic range of 10 Hz to 25,000 Hz....
We found this white noise generator circuit in old European documentation, but the components used...
We found this 1 A switching regulator in an Electronics Now magazine from April 1993. The...