After completing the Elecraft K1 and being very pleased with its performance I decided to jump in and build a K2/100 with a few options added.
The Elecraft K2 is a build from scratch kit where all the components and the circuit boards are provided as a package available from Elecraft. The kit has been around since about 2000 and there are a lot of them out there. I decided the K2 would fit my needs for a few reasons. Its very low power consumption on receive was my number one reason. With the base K2 before I install any options its current draw at 13.8 volts is a mere 180-200mA. In comparison to my Ten Tec Omni 7 which is about 2.5A and the Yaesu FT-817 which is about 1A. I run my shack on battery which is charged by solar, so power consumption is a big factor for me. The other reason I opted for the K2 was because its not a black box transceiver. I like the idea that every component was installed by me and I understand how it works, which I think is important and keeps in line with the traditions of Amateur Radio being a “technical” hobby.
The K2 Kit arrives in a white box with all the components in bags and a nice well printed fairly thick build/user manual. You build the radio up in sections, first is the control board, then the front panel and then the main board is done in two phases, phase 1 is to get the receiver working on one band then phase 2 gets the transmitter components added and the remainder of the receiver stage installed. What is nice with this approach is that not too many hours into the build you get to turn something on and test the front panel and control board, then shortly after you get a 40 meter receiver. The idea behind this is that you get to see results fairly quickly and also test the build in stages.
Identify all the parts
The first thing I done was to identify all the parts for the control board and place them in a box with dividers. I also kept the static sensitive components inside the anti static bags.
K2 Control Board assembly
This is the start of adding the components to the control board.
This is the completed control board. Since I really took my time and aimed for perfection this took roughly four hours work.
Front panel assembly
Next step was to build the front panel board assembly. This picture is prior to adding the encoder and sub board.
When you get to the encoder section, I should mention here too that you have to make sure ALL the leads on the encoder board are flush cut and also use some form of insulation to prevent the encoder board from making contact with the control board. When I flush trimmed the leads that was enough, however as a precaution I also insulated it with some black tape. The new encoder for the VFO has a board which you have to put a few components on, this is slightly different from the original K2 design, but due to parts availability the update was needed.
Main Board assembly
The main board gets a few components added to allow the control and front panel boards to be powered up and tested. As you can see there are a lot of empty holes waiting on the huge bags of parts to fill them.
Phase 1 testing
This is the view at the end of the first phase where the control board, front panel and main board are mounted in the case ready for the phase 1 testing.
Another view with the radio ready for phase 1 testing
From the front.
Phase 2 assembly
After the initial phase of tests are competed you get to pull it all apart again and add more components. The picture below is at the end of phase 2 ready to test the 40 meter receiver section and do a few alignment procedures.
There’s a sub board that has to be installed in the main RF board, so this is what it looks like before its installed.
There are a number of toroids and transformers to be wound. These are hand wound carefully and the enamel coated wire is very carefully striped and tinned with solder ready for installation. Each one takes a bit of care and attention and ultimately a fair bit of time to do. Pre-wound toroids are available at a cost from a 3rd party, but I felt that it was cheating myself not to wind them by hand, it was also easy after a couple of them. There a a large number of these to wind, I think about 30 or so.
The green and red wire cut to length ready to wind on the core.
First winding of a transformer.
The transformer installed after both windings were done and the leads trimmed. Its very easy to miss a bit of the insulation and cause a poor joint so what I done was to use a gas lighter and sand paper to remove the insulation, then once I installed it I used my multi-meter to make sure the resistance was less than one ohm. Anything greater than that indicates a poor job! I learned that from the K1 build.
Once again the boards are put into the case side panels ready to power up again. You can see there are still a lot of empty spaces on the main board, so a lot more work to do before its finished even though at this stage it will work as a 40 meter receiver.
Phase 2 testing
First time powered up with the phase 2 section completed.
Below is the K2/10 completed from the front and back. As you can see there’s a lot of components in there.
First impressions of the K2/10
Now the base K2/10 is working and tested I have a really nice working radio on all bands. Its top power is about 15-16 watts and at this stage its all working well. From the initial alignment I noticed now I’ve started to use the radio its about 200Hz off frequency relative to the display, and I’ll fix that when I have the top off the radio again to install the first option. The adjustment to get it bang on frequency requires a full re-alignment so I wanted to use the radio for a short time to make sure all was well with it before changing anything.
My first option to install will be the 160 meter and receive antenna board and connector. I have a receive antenna which helps with some of the local electrical noise so it will be useful to add this first. After that I’ll add the audio filter/clock and then maybe the SSB option, but I probably wont spend a lot of time fully setting that up initially since my microphone is made of a big lump of brass! I ordered the SSB option so I have it for the future should I decide to return to the dark side one day. The final option I’ll add will be the 100 watt amplifier, I am leaving it to the end since its part of the top of the case and would need moved any time I open the radio, so it seems more logical to add it last. What is nice is when you buy the 100 watt option you get both the base K2 and the 100 watt case top.
Audio Filter option and 160m board
As I mentioned above, I installed the 160 meter/2nd Antenna option, it was a really easy one to do, not many components to solder into the board.
After that I completed and aligned the audio filter. I’m glad I got that as it does make a difference. If you never had one and didn’t know the difference then you wouldn’t miss it, but not I have it I wouldn’t want to be without it.
Build the KPA100 Amplifier module.
Now, the next big job is to build the KPA100 amp kit. I’ve started it and got the first stage tested. I’ve then wound the inductors and I’m about to start on the transformers. A few pictures below showing the progress at various stages.
Start of the build after I sorted the components into groups ready for installing. One thing I like to do is to tape the capacitors to a card and put the values and sometimes also the component numbers on the card so its easy to select the correct part. Capacitors would be really easy to install the wrong one by mistake. I have used this method for 20 years and so far never installed the wrong one.
Now with the relays and a few other components added.
This is the board almost ready for phase 1 testing in the K2.
After a first time success on Phase 1 testing I moved onto the rest of the build which involved adding the remaining components and winding all the toroids for the filtering. The picture below is the completed KPA100 ready install in my K2. This module includes a heatsink which forms the replacement top cover for the radio.
I installed the KPA100 in to the K2 and its now fully functional, I get well over 100 watts on every band. Taking care of the details and taking time with all of this build allowed me to build it and get everything right first time.
Note on winding the coils/transformers.
I though it was worth mentioning my method of winding the coils since building a K2 with various options involves winding quite a number of transformers and coils using enamel coated wire. I figured out a fast and reliable method of doing this so thought it was worth sharing. I wont repeated the excellent details from the Elecraft manual on how wind them and count the turns. This writing is more to show how I strip the leads.
First I select the core, and cut the wire to the correct length.
Then I wind the desired number of turns on the core. Also at this stage look at the board where it will be installed and make sure you wind the wire in the direction that leaves the leads on the correct side matching the holes in the board. If you get this the wrong way round when the leads are pulled tight it pulls the coil round and wont sit in the correct place on the board. That would look ugly and also cause it to strike other installed components or prevent you from installing others. Any that are wound in the wrong direction need to be re-wound.
Next is to strip the insulation. I use a gas burner torch for this step. I carefully burn off the insulation. Take note though, the fumes from this step are poisonous, where I work I can open the door to the fresh air and I do this step at the door.
After the ends have been burned off make sure the winding’s haven’t been melted or altered.
Next is to use a bit of sandpaper to clean the ends off ready for soldering. I fold the paper in half and pull it over the ends until its a nice clean and shiny copper finish. Its worth tinning the leads with some solder at this stage.
Then install it into the board.
I have made quite a number of contacts with the K2/10 so far. Now when I need it I have the extra power. I find that 25 watts on CW is plenty, so having over 100 watts available is more than enough! Since I completed my K2 I have make it my primary radio and I cant see any need for anything else.
KAT 100 150 watt external tuner for the K2
Below is the stages of me building the tuner.
Here are all the parts used.
I sort the capacitors by value and type to make sure there I don’t make any mistakes installing the wrong value. Some capacitors have the same values but are different types or voltage ratings and its very important to use the correct type.
The switching relays are installed all in one go, you insert them into the board then place a hard book on top, flip it all over then solder them all in. Thats a lot of solder joints in one go. It would be easy to miss one in this step if your not paying attention.
Here the are all soldered in.
Next is the inductors, I wound them all, then striped the enamel and tined them all before installing them. I enjoy wining these.
The front panel with the SWR LED’s is built up on a small board. This is it after I installed all the components and was about to install the LED’s.
The completed front panel installed onto the main board.
Now its all complete. You may notice a missing variable resistor in tis picture, the one supplied with the kit had a broken leg, so I had to wait on the replacement to arrive while I completed the rest of the build.
First impressions of the K2/100 with KAT100 Tuner
Here is the K2 sitting in my operating position with the KAT100 below it. Everything worked first time and it can tune pretty much anything i connected to it! Quite a nice matching pair.
Now that the K2, and the tuner and the K2 options are all built tested and working together I’ve been enjoying using the radio. I have quite a number of contacts in the log with it now.
What’s next? Maybe the SSB option, but I’m not in any hurry to do that as I don’t intend to use it. CW is my mode of choice! I also have the noise blanker option, but again I’m not sure if I’ll install that. I don’t really need it.
Thank for reading, Best regards and happy hamming! If you have any questions about this project contact me, I’m always happy to answer them.