> -----Original Message----- > Interesting indeed. > > That approach flies in the face of decades of design convention; as a rule, AM > rigs either use the same supply for mods and final, or as the rig gets bigger, > the mod has it's own supply which is usually a lower voltage than the PA plate > supply. >
Greetings, Mr. T! Here are a few random thoughts of mine on this subject. First, I can think of the following arguments FOR using a common power supply. First, cost & space savings. Second, with a choke input supply, the class C final maintains a minimum load on the supply, reducing the size of the choke required to maintain critical inductance. Otherwise, the separate modulator PS would need to be capacitor input, or would have to waste a huge mount of power in a bleeder resistor to maintain the required minimum load on the filter. I think the historic reason for a lower-voltage modulator PS in the case when the supplies WERE separate originates from the conventional wisdom that the audio power required to 100% plate-modulate a class-C final is 50% of the class-C plate input power. But this (1) ignores losses, (2) ignores the "headroom" required for clean modulation, (3) ignores waveform asymettry, and (4) perhaps most importantly, assumes a modulation transformer of the correct turns/impedance ratio can be had. These days, we're lucky find whatever mod iron we can in the power class we need, and build around it. It is often the case we need to run a higher voltage on the modulators than on the final to achieve enough audio voltage at the mod tranny secondary to properly modulate the final, with the iron we are able to scrounge. 73, -Larry/NE1S ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
