Total posts : 45366
I have an AM25 (not sure about the C on the end) and it was my main unit for a while. I did quite a bit of experimenting with it and found it to be a good “tinker” unit.
I never had a hum problem but the modulation transistor did get pretty hot. I mounted it on an external heatsink. This works since the only signals on it are DC and audio and the RF is bypassed. The RF output FET doesn’t get hot enough to be a problem as mounted on the board.
Using a resistive load, I ran a series of tests and found that the output circuit is not sensitive to load from 10 to 100 ohms and the transmitter will drive most antennas with no problems. The input and output power does change with load with the maximum output power happening at 23 ohms resistive load.
The modulation does not go to 100% without distortion as observed on a scope, but is sufficient to give a decent audio signal with lower modulation.
Though I had no hum problems with the wall wart, I ran mine from a 13.8 VDC 3 amp switcher I had in my junk box.
I switched to the SSTRAN primarily because I found the final input power on the Ramsey greatly exceeded the 100 mW limit for part 15.219 operation and because the SSTRAN has the built in limiter/compressor and dual audio input with internal mixing for stereo sources. The measured final input power on my SSTRAN with a tuned antenna was 93 mW.
Here’s a link to a post I made some time back regarding the input power on the Ramsey:
If you use the search function for “AM25” you’ll find some more posts on this board.