I've been trying out some homebrew amplifiers for a while, trying to get one to work, and this simple design preforms pretty well.
https://postimg.cc/gallery/CMGRg9hIt's based off of a 1W amplifier design that can be easily found on the internet, but with a BD-139 transistor. The BD-139 can take up to 80V and handle 1.5 Amps, but here I've got 38V going into it. With the extra resistance needed before the RF choke, the 39 Ohm resistor on the output was eliminated. A few other modifications were made based on what I had, and performance. The antenna hasn't been trimmed yet in this test in the photos, but since trimming, I've got up to 5W output. The input to the amplifier is a 26MHz Michigan Mighty Mite with AM added. To make the coils and get them to the right inductance, they should be wound with an extra turn or two, and then the last couple turns bent back 'til the right inductance is reached. I used a Hantek 1832C LCR meter for this. The trimmer caps are cheap 5-40pF ones from eBay, and the coils are made of 20 AWG magnet wire, AA battery used for wrapping them. Boost converter for the amp is also cheap on eBay. Meter is not cheap though.
A note on these AM mighty mites for the higher end of the HF band. Its commonly said that mighty mites put out half a watt, but that's not right in this case. I'm no expert, far from it, so take this with a Kg of salt. The actual power according to the fancy new RF power meter I got, was only 50mW, a tenth of what I assumed it was before I got the meter. From my (limited) understanding now, there's two reasons why this is (probably). One is that to get good sound quality out, have to tune the cap on the mighty mite a bit past the peak output. Two is that the efficiency probably drops off with increasing frequency. I've made a mighty mite even for 60MHz, so it still works at much higher frequencies than they are commonly made for though.
Anyways, looks like WBLS is nearly ready to roll for real this time.
Topic: Stupid Simple Couple Watts Amplifier (Read 123 times)