I went from below the noise to just about workable with this power level on 40 meters ssb. I have worked several stations in South American and in Europe with this setup. The IRF510 is not the cleanest device, but a higher supply voltage (I use 30 volts) and push pull configuration all helps. If I drive it too hard though, it distorts, so I have to be carefull with the drive level. This amplifier works well and I get good reports on the air. It is probablly overkill for this power level. Those in the amplifier use type 43 material. You can see that the amplifier is in a no frills box from.
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I tested them with a signal generator and my Power Meter. So far I have only constructed filters for 20M and 40M because those are the only bands I can I calculated the number of turns needed on the torroids with a spreadsheet like this one.
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I designed the low pass filters with ELSIE, which comes free with the ARRL Handbook. The box contains the amplifier board and the low pass filters. If you find that your amplifier is producing broad band noise and oscillating, check to see if it is the driver, rather than the amplifier itself. Adding an attenuator worked well and solved this.
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Occasionally, if the load was mismatched, the PA driver (in the radio) would oscillate or produce broadband noise. It made sure that the radio saw a clean 50 ohm load. One key to success with this amplifier was an input attenuator. Otherwise these heatsinks are very cheap at If you have a better heatsink in your junkbox then use it. I don't have a fan, the heatsinks are inside the box and everything survives normal SSB operation well. Much bigger and more expensive heatsinks are usually found in these amplifiers. This is not the approach that others recommend. The whole board then acts as a heat spreader as well as the ground plane.
I built the amplifier ugly style using small heatsinks flush against the copper board. With the current limit circuit the amplifier now survives transmitting into any SWR from an open circuit to a short. I built it into the Amplifier because the power supply, which is also homemade, does not limit until 7 amps. You can build it into the Power Supply or into the Amplifier. The amplifier draws more than about 3 amps from the PSU. Once I got tired of replacing the FETs, I built a current sense circuit, which shuts off the bias once It was quite a shock when the first one was destroyed because it made a loud noise like a rifle being fired. In fact I blew a small hole in one and another into several pieces. I destroyed many IRF510 FETs during testing. This was an experiment for me and aimed mainly at 40 meters. I ended up following an article by Mike Kossor, WA2EBY, published in QST in March 1999,īut I kept the design simpler and did not look for the flat, maximum gain across all bands that he was after. It was inspired by Fig 2.101 in EMRFD, the AA3X amplifier,īut there are well documented examples online. The circuit below is an old one, repeated many times. I followed that driver with Fig 2.98, which uses a single IRF510 and generatesĥ watts easily, 10 watts with higher supply voltage. The yahoo EMRFD group and finally got it working. It took meĪ while to get that curcuit to work because I had used a wire wound resistor in one of the emitters by accident. For example theįinal stages in the Gateway 40, which typically drives this amplifier, used Fig 2.93 in Experiemenal Methods in RF Design. My advice is to build straight forward building blocks and test each one to make sure that it is working.
In fact, it was harder for me to create the 5-10 watts of drive that this amplifier needs, than is was to build and test thisĪmplifier. I have had my fair share of difficulty with obtaining high Many people build low power equipment and find amplifiers difficult. I found I could work stations inĪbout a 200km radius during the day with 5 - 10 watts, but at night I could work no one at all. I built this amplifier so that I could be heard above the QRN and QRM on 40 meters in the evening.
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