Here is a picture of a clever crystal radio
that Larry, WR6K sent me:
A crystal set using tapped coils selected
with dip switches. Other tuning features are a fixed capacitor and
permeability tuning (that means he moves the coils around on the ferrite
cores to change the inductance). Probably used a 10x magnifying glass
to solder those dip contacts.
Here is a pic of the "Zero Cost" Detector.
The PCB is about 1/2" wide, and about 2" long. Cut a strip
of copper out to isolate the two
sides. It is easily attached to the Xtal radio base with the double
sided sticky foam. Or, put a hole in it and use a screw. The
clip used here is a paper clip that has
been shaped. It works OK,
but a large safety pin works better. However, the safety pin is very hard
to cut and shape. I have also used a mini-alligator clip from Radio
Shack to hold the Xtal. It works very well for holding very small
pieces of Xtal, but costs about 12 cents. The inverted "U" shaped
wire is #16 Brass. I bought
it at a hardware store. The mineral shown is Iron Pyrite. Iron
Pyrite is easy to find, works well with a rather stiff Cats-Whisker, and
stays put. It works well in this type
of detector stand, because it is
not finicky. This is not a good of stand to use with Galena, because
the Cats-Whisker must be much finer, and not as stiff, the hot spots are
harder to find, and pressure must be very light. Obviously, with this type
of stand you have to bend the probe past the point you want and hope you
did it right so that it ends up in the right place. This is not too difficult
to do with practice, so long as the adjustment does not have to be perfect.
The CW on this one is #28 Phosphor Bronze, but a #28 Brass CW works very
good too, and is easy to find at the local hardware store.
All in all this is a
good Zero Cost Detector stand that is easy to make and works well with