The Atwater-Dave Breadboard — #39 Radio)
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