Just tweeked up my Ramsey AM-25 a bit.
I was feeling that I was not getting as much modulation as I should before it begins to distort, so I sat down with the schematic and it became immediately clear where to look.
The power supply is unregulated DC from a wall wart. The audio modulation output transistor is biased at approximately half of the supply voltage to put the modulator transistor in it's linear region. The RF output is high-level modulated. This puts this particular transistor in a sensitive position with respect to supply voltage vs. bias vs. modulation quality. The Ramsey manual says to adjust the bias to exactly 7.1 VDC, presumably that assumes you have exactly a 14.2 VDC supply. Well, I'm sitting at 15.2 VCD or so on the supply.
So what I did was, I put the scope on the modulator output with a 1 kHz sine wave at the audio input and adjusted the bias so that as I begin to over drive the audio input to the point where both the tops and bottoms of the audio modulation start to clip at the same time, indicating that my bias is centered for maximum modulation. That turned out to be something like 7.455 volts. So the manual really just gives you a starting point, this is really a critical adjustment if you want to get maximum performance.http://www.sudburychange.org/index.php/faq/31-general/54-am-25-rf-output-with-1khz-sine-wave-audio-saturated-p-p.html
I'm seeing better performance now, and a much better sound quality.
I think the Ramsey AM-25 could really benefit from a regulated power supply (I will be remedying that using one of my boost/buck switchers http://www.pikeaero.com/vr134
recalibrated for 15 VDC).
The AM-25 is a cleaverly simple PLL synthesized transmitter, in order to get peek performance, it does require some care and feeding, but if you're into that, it's very rewarding.
Anyway, had my station down for a while while I fiddled with the AM-25, just wanted to report what I turned up.