Where the Neophyte had been left off was with a breadboard prototype which in some fashions functioned; the oscillator was percolating (I think), the tuning capacitor provided some level of variability in the oscillator output (I think), and the front end was can be tuned (this I know). There is yet a distressing lack of ability to actually tune an intelligible signal, but in the absence of anything more than my cheap DVM, I realize that I'm at the limit of my testing ability beyond what I described in my last Neophyte post.
Since I was at an impasse here, and I noted an exceptional amount of "hand capacitance," I decided to rip the prototype out of the breadboard and assemble it Manhattan-style on single sided copper boards. Soldering well is a bit more difficult than I remember, but then again I come from the illustrious school of "the bigger the glob, the better the job" solder training. I never had the manual dexterity to get in to the Navy's 2M (Micro-miniature) repair soldering courses of instruction. What really helped here was the Manhattan accessories offered by Rex Harper (W1REX) at his storefront www.qrpme.com. I used his MePads to mount the DIP sockets for the LM386 and SA612 chips...saved me several toasted chips, I'm sure. The MeSquares were equally awsome for rapid building.
What we have so far is the audio stage centered around the LM386 amplifier chip, along with the low pass filter coupling the down-converted audio from the SA612 mixer chip. The "dancing capacitors and resistors" in the corner of the board are the Zobel network and output coupling capacitor which filter and feed the amplified audio signal (if I ever find one) to the headphones of the receiver.
Don't ask me why I did it that way; I think it was a gut aesthetic call that struck me in the cloud of solder smoke. From a technical perspective, shorter leads tend to be better to reduce unwanted coupling and other feedback problems, but as these components are themselves filters I judged the technical risk to be low. Now, if I have to eat a little crow on that estimate, you can see I've backed myself into a corner (pun absolutely intended) since there is no copper left to which I can move the dancing components. If that is the case, I'll end up moving the two capacitors and the resistor to the headphone jack itself where it will be mounted on the front panel.
If you are not familiar with Manhattan construction, I highly recommend it to anyone interested in electronic construction. Back in the Navy days, I did some custom electronic construction of some data collection systems and had a horrible time with PCB design and etching; the chemicals are awful and my success rate was abysmal.Manhattan style allows one to build up the circuits in a very logical, easy to design manner in which everything is visible and available to the eyes and fingers. For your further reading, I'd recommend Chuck Adams' (K7QO) two articles on the basic and advanced techniques (both links are PDFs):
Now, I've not applied power and done rough testing on this yet, but visual inspection and ohmmeter testing show no gaps or solder bridges. Tonight I'll try to get some of the mixer, oscillator, and/or front end installed.
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