Monday, February 5, 2018

The Venerable Elecraft K2/100

Elecraft K2/100 with KAT100 tuner, as it sits on the desk.

I cannot believe it has been fifteen years since I built the Elecraft K2/100!

When I first got interested in amateur radio, in the mid-70s, I wanted to build my own rig. While I studied for my novice, an elmer of mine insisted that each ham should build his own transmitter. He gave me some parts, and I made an honest attempt, but the "Novice" Transmitter didn't actually work until many years later.

Later, while preparing for college, I tried building a QRP transceiver I might use in the dorm. I built a 7 MHz FET VFO, a direct-conversion receiver, a 3 watt transmitter, and a even a KOX or Key-Operated Switch to do semi-break-in with side-tone and an relative power and S-meter.

This design never did work. Never heard a peep out of the receiver. While the transmitter produced a couple of watts output, it couldn't decide if those watts were on 7 MHz or 14 MHz. The key mistake I made in my youth was building the entire project before testing anything. The VFO worked, the KOX worked, but that was about it.

I had tried to build my own designs, without a lot of success.

I noted the Elecraft K2 introduction in 1999 with interest, but I wasn't excited. While relatively inexpensive, it only produced 10 watts output. I needed a replacement for the venerable Kenwood TS-430S, and that meant 100 watts output. When Elecraft announced a 100 watt PA for the K2 later in the year, I was hooked. Best of all, I could buy the rig in installments, adding options over time.

I joined the Elecraft mailing list, and read everything I could about this great little rig. Sold! On March 1, 2002, I placed an order for a plain Elecraft K2/10 and would receive Serial Number 2548.

On arrival, I spent and hour or two each night building. This wasn't something you could knock together in a couple of evenings. I wanted to do a good job as well, to savor the process, instead of just slap it together. In total, the basic K2 took me nearly 30 hours to build.

Wayne Burdick (one of the Elecraft founders) at some point asked me for any building notes or comments on the K2. This gives you an idea of how grassroots a company like Elecraft is. I sent him a series of four notes with my impressions and some detailed comments. I don't know if he actually used this material to improve the K2 assembly manual, but it's a nice thought.

The K2 is no Heathkit. A real Heathkit would have more drawings and diagrams at each stage of assembly. But, hey, Heathkit is out of business and Elecraft is not.

Any K2 builder can spin yarns about the joys of winding toroids. There are dozens of them in the K2. Frankly, I didn't have that much trouble winding toroids. Tinning the toroid leads, on the other hand, was a real pain. Especially when I didn't tin them up quite far enough and had to do it over.

After 20 hours of construction, I did the Alignment and Test II section and was listening to 40m signals coming through the receiver. Given my previous experience, this was very exciting. You have such a feeling of accomplishment when something you built actually operates.

For the most part, the K2 worked flawlessly after construction. I did have a problem with flaky AGC action, which was fixed with a resistor substitution and a replaced transistor. I also had an intermittent INFO 080 (the dreaded AUXBUS failure) which was caused by a bit of waxy burnt flux between two pins on the control board. The Elecraft mailing list and support email address gave me the information I needed to diagnose these problems.

With the basic K2 built, I started ordering and building options. The KSB2, the SSB module, was up first. The KSB2 has the densest board of all the K2 kits, making it the hardest to assemble. And the FT23-43 cores were so tiny, I originally thought they were fiber washers.

After the KSB2 came the KAF2. I had read enough to know that the K2 audio had an unpleasant hiss that was knocked out by the KAF2 audio filter. Beyond that, however I never found the audio filter to be that useful. While the KAF2 also has a real-time clock, I never found much use for it.

Next was the KNB2, the noise blanker. Having used the one on my Kenwood TS-430S, I felt that a noise blanker would be a required option. But the KNB2 isn't terribly effective at eliminating the noise sources I most often encountered. I was able to determine it was working, and later managed to make modifications to improve it's effectiveness.

The last option for the basic K2 I built was the K160RX -- which has to be the simplest option board I've built. Once installed, I had a very functional K2, with 160-10m coverage, CW, SSB, Noise Blanker, Audio filter. All I needed was to wait for the KPA100 option.

And, indeed, as soon as it was available to order, I placed my order the same day. And then I waited.

Fate intervened, however. While I was waiting for the KPA100 to ship, I was laid off from my job. This was the summer of 2002. The internet bubble had burst, and there were several shocks to the economy, what with the 9/11 tragedy, and the Enron and Adelphia Cable financial scandals.

Without employment, spending hundreds on the KPA100 didn't seem wise and I cancelled my order. I feared I might need to sell my K2. It took me nearly four months to find a new job, as the market was really tight. But as soon as I had a new position in hand, I re-placed my KPA100 order.

I had some trepidations about the KPA100, but it went together pretty easily, and it worked like a charm right from the start.

At this point, the K2/100 became my main rig. With computer control -- something that I had coveted for years -- contest band changes became much easier. I loved it.

Close up of the friendly face of the K2. 
Once built, for a few years I was regularly tearing into it to make modifications. The improved 2nd XFIL mod, the KI6WX improved CW filter rejection mods, alternative AF gain control. The massive A-to-B upgrade. The BFO temperature stability mod. Redoing all of the crystals with the K2KSB2XTALS mod. The KSB2 firmware update to v1.08. The PLL temperature compensation mod. The KPA100 Rev B upgrade with upgraded shield. K2 firmware update to v2.04. K2 Keying modification. The QSK improvement modification. KPA100 current consumption mod. The power control mod.

During these first few years, I also added the KAT100, the KDSP2 and my favorite, the Finger Dimple. The KAT100 really made the rig more versatile. The KDSP2 helped out on SSB with some needed bandwidth filtering, and the auto-notch filter. But the Finger Dimple made tuning the rig a much more comfortable proposition.

From Mid-2005 until 2010, K2/100 served as my main rig without any modifications. 2010 brought a flurry of final mods. The VCO Shielding mod. The KPA100 Rev D upgrade. The KNB2 response and threshold sensitivity mods.

Once I finished all this, I bought the Rework Eliminators kit -- that enables one to swap out option modules without making changes. I don't believe I've used them.

Although the K3/100 replaced the K2/100 as my main rig, I still use the K2 regularly. It is pleasant to listen to and quite capable. The K2 has earned an honorable place on my operating desk, and deserves to be called a venerable rig.





- Need good K2/100 picture.


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