Let's put on the capacitors that give the correct tuning ability and then wire 'er up!.... here is the schematic!
I had a bit of time trying to figure out the caps on the bandspread, how it worked and all, then I remembered my basic capacitor rules: Capacitance decreases in series, and increases in parallel. OK, now I get it! Here is the pictures
Notice my little trick to minimise shorts on the band cap selector switches. (Sure hated to waste that whole other side of the switch though. I wonder what I could use that for?) They were kind of fun to wire but the ones on the bandspread cap (closest to tuner) were just pure tough. It was worth it to take my time and go slow! The hardest part was trying to find enough 50pF ceramics. I had several 47pFs, but not enough 50pFs. So, I did the best I could with 47pFs, 1pFs, and even a few 2's and 3's all soldered in parallel to make 50pFs. You can see where I doubles and even tripled up.
I used TeflonŽ wire on the hook ups, color coding as best as I could. I think I made green/blue grounds and brown/reds were for signal, also yellow, or something like that. I highly recommend the TeflonŽ wire. It is pretty hard to melt with standard soldering temps. It can be a bit tougher to strip, but I have a sharp X-acto blade (mine is a #10 scalpel blade, but you get the idea) or a good wire stripper, no worries.
That little two position DPDT switch selects high or low scale on the band spread switch.
If you look REAL closely, you can see the 1N34A diode and its insulation coming from the inner contact in the 2 o' clock position on the far left switch, running down to attach to the "hot" side of the headphone jack. I used a stereo jack because it was the only one I had in my junkbox, I suppose a mono work work just fine.
Well, without getting into the theory, it works pretty good! When I first fired it up, AM BC stations were blasting in. The antenna trimmer really helps to cut down BC stations. There are a lot of combinations I will try to maximize selectivity and sensitivity. I am using the Radio Shack "Amplifier/Speaker", stock #277-1008C, which has a input impedance of 5K Ohms, great for crystal radios. It amplifies just fine. I don't have any way of reporting on sensitivity, selectability, or whatever, I can say that I was pretty jazzed when I heard Duetsch Welles from Germany and Radio China from Beijing. Walt has also used two of the speakers in series, one to amplify directly and then the other to "amplify the amp".I bought another one today and will try that out.
Here's a neat letter I got back from Walt. I wrote him a letter, using an address I found on QRZ.COM. It was good to hear from the guy who actually designed the rig. Here is the letter.
Wow! Had enough?click here to return to my radio pages
