January 30, 2011 – Building The Small Wonder Labs Retro 75 AM Transceiver

Been as busy as a beaver over the last few weeks with radio kits, and have more coming this week! As from Elecraft, I’ve also enjoyed kit from the good folks at Small Wonder Labs, www.smallwonderlabs.com, building a number of their kits over the years. Recently Small Wonder Labs came out with a simple, QRP power AM transceiver kit, called the “Retro 75”. I had looked at the kit many times, but always had other projects, so I finally ordered it a few weeks back. Last night I started the Retro 75 build, was up to 4:30AM, lost track of time and really was enjoyed the project. I finished up the details this afternoon, and I estimate that it took me about 12 hours of total time. One could do it in less time, but I wanted to enjoy the process, and the moment it ceased being fun, I stopped and took a break. I also spent some additional time to make sure the solder connections and lead dress looked just right. In fact, I initially ran the wiring for the control and jack leads above the chassis, but it looked a tad too cluttered for my taste. Wanting to really enjoyed and be pleased with the project, I redid the wiring, and ran it under the PC board. The efforts were worth it, as the rig played the first time out. I did find one wiring error during my pre-power up testing, I had reversed the T/R and Power leads, easy to do as they are next to each other on the board, and I was working under the board rather than on top. During the alignment stage, the set was hearing shortwave stations with just my finger as an antenna, and even the two variable indictors, T1 and T2 did not require much tweaking, both were just about spot on. Some notes about my build, as I mentioned earlier and per the suggestion of Dave K1SWL, I ran my control and jack leads under the PC board, rather that on top, it makes for a cleaner looking build, used heat shrink tubing to keep the lead dress neat. The 3A/B/C capacitor selection confused me at first, it was not until I read later in the manual that I fully understood that those different values were used to set the turning range. Since the instructions are rather free form, I chose to build using component types, rather than board areas, this seemed to speed things up as I could sort the values before install. So the caps went first, then the resistors, inductors, etc. The system worked pretty well, and I used the component listing as check sheet, marking off each part on install. I’d ideally like to see some sort of plug in header for the wiring, so the board could be removed for service, inspection, but this is by no means a necessity, also a plug in xtal holder would be nice, so could sway out xtals, guess I can implement pretty easily, and both options would only add to the very reasonable cost for the kit. I bought the optional enclosure, glad I did, works well with the rig, With that said, I would really love to have the anodized aluminum case like the ones offered with the Small Wonder Lab DSW series back in the late 1990s, but that is something which I am working on. Power levels, for AM carrier, varied between 3-4 watts without modulation, right on spec, as you can see by the Elecraft power meter photo. RX side seems to work well, nice and sensitive, pleased about that, looks like a real bargain for the money. In summary, the Retro 75 is one very fine kit, a great weekend project, quite well designed, well priced, looks like Dave has hit another homerun with this one!

Beginning the Retro 75 build, note Elecraft K3 in background for entertainment.

Retro 75 built and installed in case, all wires routed under board for clean lead dress and appearance.

Overview of the transceiver, sitting on top of build manual for size reference.

Retro 75 ready for on air testing, fine little RX was well.