Experimental receiver for VLF. I received electromagnetic (radio) signals between 14 and 22 KHz with a capacitor of 4,7 NF over the showed coil. The schematic is identical to that of the storm detector IV (with the 6088 Tube), the coil is differently constructed. There is one more transistor amplifying stage + an AM detector (germanium diode) at the end of the extra stage. Input (basis) and output (collector) capacitor to the extra transistor can be between 390 N and 470N. The coil (tank circuit) can receive frequencies between 4,5 KHz and 25 KHz. At 4,5 KHz the capacitor is approx. 20 N (test), at 14-22KHz the capacitor is 4,7 N. Test the resonance of the receiving coil (= received frequency) by connecting an LF generator with a capacitor of approx 50 P to the top of the coil and a scope on a location before the AM detector. Turn the frequency and see where the coil "peaks" with a certain location of the ferrite rod (more in-out).(on the channel of All American five radio on YouTube there is a clear demonstration of what I mean in the video "resonant frequency"). Coil is 7 x 200 turns 0,1 mm enameled wire, wound in sections of 200 turns, on cardboard tube of approx 1 cm diameter. Ferrite rod must be moved in-out the coil to tune in on the maximum of the received Very Low Frequency. You can see on the scope if you have tuned in well. Turning (changing the direction) of the ferrite coil has a great effect on reception. I don't know where these radio signals come from (not from computers I presume). The noise you hear on this video was created by my digital camera and received. So I could not get too close. In the showed video one of the 200 turns sections is shortcut, so the effective coil is 6 x 200 turns. If there is interest I will upload the complete schematic.