This circuit was found in a Popular Electronics from the 90's. Its purpose is to detect the ionization of the air. The meter can be replaced by the current scale of an ordinary multimeter.
This mechanical reverberator circuit for guitar was found in the February 1970 issue of Radio...
Found in an old English publication this circuit uses a dual gate MOSFET. Coils not specified....
This is the receiver for the previous circuit transmitter. Similarly, no information about the...