> leads to severe distortion or splatter. I again hold the > opinion that the > real bad signals heard are due to to PAs being operated > with no ALC feedback > to the exciter feeding it and operators being clueless to > this.
Most amplifiers have very crummy ALC detection. All they do is same RF level at the cathode of the tube, and that doesn't indicate excessive drive or nonlinearity at all! In most cases however people are just kidding themselves when they connect ALC from an external amplifier. All the ALC from the amp does is sample the same thing the radio's directional coupler does, so the external ALC is redundant to what the radio already has... except not as accurate or stable from band to band. In some later tube amps I used an ALC detector that samples grid current (and in a few cases grid current and plate current). This does work to limit excessive drive, but in most radios the ALC has so much gain and group delay the system will motorboat. The solution was to add a pot that limits maximum ALC voltage, so it is a two-control system in the amp. Still, it is better to do the ALC ahead of all the signal path time delays, like the slower propagation through filters. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
