Building An Amplifier

Elecraft KPA500 Amplifier

Elecraft KPA500 Amplifier

I have been planning to add a medium power HF Amplifier to our station for some time now. The plan was to use an amplifier of this type for two purposes –  as an amplifier for Anita’s (AB1QB’s) position at our home station and to have an amplifier that we could take along on DXpeditions and other portable operations. After doing some research, it looked like the Elecraft KPA500 Amplifier would be ideal for this. It is small in size, can operate using either 120 VAC or 240 VAC power and has a quite reasonable weight of 26 lbs.  After dropping some not so subtle hints, I received a KPA500 kit as a holiday gift.

The Elecraft KPA500 is a no-solder kit and requires 4 – 6 hours to assemble. Just for fun, I decided to make a time-lapse video of the assembly, checkout and an initial QSO with our KPA500.

The assembly of the kit was quite straightforward and I was able to complete it in about 5 hours. The amplifier worked fine after assembly. It  performs well on all of the Amateur Bands from 160m – 6m and delivers its rated output of 500 W with 25-35 watts of drive power. The initial QSO in the video was made using our Elecraft KX3 Transceiver which provides a maximum of 12 watts of drive power to the amplifier. As you can see in the video, the KPA500 produces about 200 w output using the KX3. I have also tested the KPA500 with a 100W transceiver and found that it produces the rated output on all of the bands and runs cool and quiet. Testing with my station monitor as well as on-air reports indicate that the KPA500 produces a clean signal.

I know that some of you may be wondering how I made the time-lapse video included in this post. I found a very good how-to webpage that explains how this is done and includes links to some good software choices to perform the various steps in the process. The software and hardware that I used are listed in the credits at the end of the video for those who are interested.

Time Lapse Video Setup

Time Lapse Video Setup

The basic setup requires a digital camera on a tripod that can take a series of still images at regular intervals. My video was created using a Nikon D7000 which took a still frame  every 5 seconds. The video required a total of about 3,900 individual photos to produce a 24 fps video that is about 2:40 minutes long. A combination of Batch Photo Editing (Adobe Lightroom), Time-Lapse Assembly, and Video Editing (Apple iMovie) tools were used to complete the project.

The plan is to couple the KPA500 with Anita’s new Flex-3000 Software Defined Radio (I got a not so subtle hint too). More on the Flex-3000 and its operation with the Elecraft KPA500 will be the topic of a future post.

– Fred (AB1OC)

If you have found a spelling error, please, notify us by selecting that text and pressing Ctrl+Enter.

3 thoughts on “Building An Amplifier

  1. Awesome video, indeed. Very inspiring. The Elecraft KX3 is an amazing rig, its topped the charts on Sherwood Enginneering Test. I onw it personally and have it interfaced with Tentec’s Model 418 Solid State Amplifier with which I had to build a custom cable to interface it with the amplifier. How did you set up your custom cable? I would imagine that you used an RCA to connect to the KPA 500 and a 2.5mm plug into the KX3. How were the wires in the cable configured.

    KJ4RWQ, 73’s. Awesome documentation of your tower as well. You guys should be proud very inspiring.

    • We used a cable kit that is available from Elecraft as a KX3 accessory. If I remember correctly, the cable kit included both a “CAT” cable and the keying cable. You are correct that the amplifier end is an RCA ping connection. We use the amplifier with both our KX3 and my wife’s Flex-3000. The changeover is accomplished via a combination of plugging in the correct keying cable from the radio to be used and using an antenna switch to connect the associated radio to the amplifier’s input.

      Thank you very much for the nice comments. We are hoping that other will enjoy and gather useful information and ideas from what we have done.


      – Fred (AB1OC)

Leave a Reply