|
Hi folks. I got the idea
for this one from a picture of an old
Atwater Kent breadboard crystal set.
I know you would rather have that one than the one I built but there is probably a few
dollars difference between the two. I haven't found out for sure but it is a good guess.
This is my Atwater Kent clone. I have always thought these breadboard
sets looked great and I had to build something like it. This is the second remake
of this radio. It had a cylinder coil without litz and the performance just didn't
make me happy. So I redid this one a little.
I started with a 15 inch by 6 inch red oak board. This is my favorite
hardwood. My neighbor kindly trimmed the edges and I put on a little golden oak
stain. All the holes were drilled with a 1/16 inch bit, then a 1/2 inch forstner bit
on the bottom (and the two holes on the top for the capacitor). I like to have the
holes recessed. The screws are one inch long 8-32 thread. I never get tired of the
brass hardware. Just something about those knurled nuts.
The focus on this project is the variable capacitor and the box that
houses it. The box is a 4-1/2 inch round box set on end. I traced and cut some 1/8
inch garolite. The box isn't perfectly round so the tracing was necessary. I then
cut the holes for the capacitor and the six countersunk holes for the little
#4 wood screws. I also decided where the bottom should be and drilled two holes
for the connection screws. Take a look at the pictures for more details.
The coil is a 4.25 inch spider coil with 11 slits. The form is made
from 1/16 inch styrene. The hub is 2 inches in diameter. I used
165/46 litz wire, making 39 turns with a tap at
24 turns for the diode. This coil, according to my little spreadsheet program,
takes about 33 feet of this wire to wind it. The inductance is approximately
150 µH.
I put a series of capacitors to allow for better tuning. The higher
the tap (A4 or A5), the lower in the band this set will tune. If moving the
wire doesn't interest you, try my #40 set,
which has two variable capacitors.
A galena type detector can be easily
substituted for the 1N34A diode. I may add one as time permits. The capacitor
is an old style made by Faradon. A 47k ohm resistor across the headphone connection
is hidden under the breadboard. This can be eliminated if magnetic earphones
are used, rather than a crystal earphone.
I found some more round boxes, The next set uses two of them
in a Mae West configuration.
73 and good crystal DX. Dave - N2DS
|
