FT-817ND Range extender!

Homebrew - Saturday 9 July 2011 20:50
Although I very like QRP. And I very like my FT-817ND. But sometimes you wish you had a few extra Watts. Especially on the low bands 80m and 40m.

5 Watts SSB on 80 meter is most of the time too low. So I build an amplifier. It's build with 4 x IRF510 in push-pull. VCC is about 26 volts. 1 Watt in is 100 Watt out. I have an attenuator so I can drive the amp with 2.5 Watt. Current is about 7 amps. So the efficiency is about 55%. The idle current (bias) can be adjusted per individual IRF510.

There is A tiny micro-controller (Attiny45) with an LM35 temperature sensor to regulate the fan. Although fan control can be perfectly done without a micro-controller. I think no project is complete without A micro-controller! Every project of mine must include at least one micro-controller! They are so cooool :-)

I have only build two low-pass filters for 80m and 40m yet. Maybe I build a third one for 20m.
The heatsink is an old Pentium 3 heatsink. This amplifier can be build under 25 euro's :-)
It doesn't have SWR protection so if I blow the fets it will cost me about 5 euro's.
By: Erwin PA7N | Permalink | 1 comment


Frank Talens PF5T

Sunday 10 July 2011 19:36
Hi Erwin,

That amplifier looks very neat and clean. You must have picked up this idea somewhere. Did you find this design somewhere in the books or did you designed it completely from scratch? If so, could you put the electric schematic on your website too. Ideal for reference-purpose for yourself but more important: maybe other hams can rebuild your design. Or better: other hams can discuss improvements or so. Anyway, this amp of yours is looking fine to me and has a nice price-tag.
Happy homebrewing! Frank.