Some weeks ago I bought a chinese amplifier kit on Ebay which came for 16 Euro / Dollar shipped. The kit took only 2,5 weeks to arrive and came in a simple plastic bag without any protection and it also came without a manual or instructions. But even if it does not work, the parts alone are worth the money. While waiting for the kit I found an interesing article from John, PD7MAA on his website. He does not only have the schematic available, he also shows how nice such DIY-projects can look like.

Especially the filter is worth a look. Building the kit was not too hard, but the surface-mount (SMD) parts are very tiny and you need a calm hand and good eyes. When I had everything assembled I tested it without a heatsink on the two IRF530N mosfets from IOR. It took not more than five seconds to kill both FETs while sending an AM carrier (1,5W drive). I ordered a pack of five new IOR IRF530N mosfets on Ebay which arrived today. After the QRL I soldered them in, and I drilled the holes into two pieces of an old heatsink harvested from an old PC power supply.

I did some power output and SWR measurements then. Numbers indicates the output and the numbers in brackets are "SWR-bars" on the FT-817 display:

 Input 80m 60m 40m 30m 20m 17m 15m 12m 10m
0,5W 60 (0) 55 (0) 40 (0) 28 (1) 20 (0) 20 (1) 13 (0) 10 (0)  8 (0)
1,0W 71 (0) 70 (0) 58 (1) 48 (2) 30 (0) 25 (3) 20 (0) 18 (0) 14 (0)
2,5W 89 (0) 79 (2) 72 (4) 58 (3) 60 (2) 52 (3) 58 (1) 60 (3) 40 (0)
5,0W 95 (1) 81 (3) 75 (4) 60 (4) 74 (3) 60 (4) 72 (0) 62 (3) 60 (0)

 

After the "measurements" I was able to work S57DX on 20m with 60W output (2,5W drive from the FT-817) and I also worked my friend Peter, DC2ZO. While in the QSO I pushed 5W from the 817 into the amp and with 3 SWR-bars on the dispay and 74W output I killed another pair of IRF530N mosfets. I will now mount a bigger heatsink, 2 fans and a case and then I will do some more measurements. As recommended by John, PD7MAA a drive of 2,5W seems to be ideal for me too.

Anton, HB9ASB already wrote an article about the 70W kit: FT-817 PA - Bausatz ohne Schema

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Youtube-video from KC2IRV:


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