so i finally finished my first scratch build, a little 40m CW transceiver based on one of the EMRFD designs. took me way longer than it should have because i kept second guessing myself and reflowing solder joints that were probably fine to begin with. anyway got it on the air last weekend from a park near my house, running about 3 watts into a linked dipole strung up between two trees.

managed 4 contacts in about 2 hours which honestly i wasnt expecting much more than that for a first outing. one of them was a station in ohio, im in western PA so not exactly DX but still felt pretty good for 3w and a homebrewed rig sitting on a picnic table.

my question is about efficiency i guess. the final is running warm, not hot exactly but warmer than i expected. its a single IRF510 and im getting maybe 65% efficiency which from what ive read is about normal for that FET but some people say they do better. is there something in the matching network i should be looking at or is 65% just kind of what you get with that part? also wondering if anyone has gone to a different output transistor and seen a meaningful difference in practice, not just on paper.

65% is honestly pretty respectable for an IRF510, those things are kind of notorious for being finicky to get right and a lot of builds dont even hit that. the warmth you're describing is probably fine as long as its not throttling up over time or anything. i ran one for a whole field day afternoon and it got warm to the touch but never caused any trouble.

if you really want to chase better efficiency some people swear by the BS170 in a class E arrangement for lower power stuff, like under 1 watt, but at 3 watts the IRF510 is pretty standard and i wouldnt tear up a working board chasing a few percent. the matching network is worth double checking though, just verify your low pass filter values against the design and make sure your load is actually presenting 50 ohms at the final. a lot of efficiency loss hides in an imperfect match rather than the transistor itself. ohio from western PA on 3 watts homebrew is a solid first contact, congrats on getting it on the air.

im also pretty new to building stuff and this is encouraging to read honestly. i have a bitx40 kit sitting half assembled on my bench and i keep stalling out. maybe i should just commit and finish it this weekend. what kind of antenna feedline were you using, just curious if you went with coax or ladder line to the dipole?