Re: Inexpensive eBay Amplifier Kits

Howard Fidel

I built the 70 watt model. I changed the 2 IRF530s to 4 IRF520s. The IRF530s oscillated and failed quickly. They also run very hot. The IRF520s run much cooler (2x as many junctions) and are stable putting out 50 watts on 20 meters. The output on 15 and 10 is less, but the uBitx puts out less on those frequencies. I am working on getting it working on all bands, but for now I just use it on 20.


On 7/11/2018 8:42 PM, Richie Chambless wrote:
The 45 watt and 70 watt amps use the IRF530, and I own both. They do work, but not for long at the advertised power. It’s very easy to push too hard on the drive and blow the FETs. The 45 watt version only takes 10 milliwatts of drive to get full power, so it can be connected directly to the BitX 40 T/R relay with a 3 to 6 dB pad (bypassing the PA). You can get about 25 watts out on 13.8 volts. The 70 watt amp needs about 1 to 3 watts of drive to work, but can produce 40 to 50 watts from 80 to 20 meters. The output falls off sharply after that. Either way, but some extra IRF530s... you will need them!

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