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Efficiency and maximum power transfer
"Richard Fry" wrote in message ... "Walter Maxwell" wrote What seems to be overlooked here is that the source resistance at the output terminals of the pi-nework in Class B and C amplifiers is non-dissipative, which is the reason they can be loaded for delivering all available power for a given grid drive, and still have efficiencies greater than 50 percent. One of the myths circulated for years, and still prevelant, is that the reason for Class B and C amps to have efficiencies greater than 50 percent is that the load resistance must be greater than the source resistance. Tain't so. ____________ Walt - what is your thinking on the point that untuned, solid-state amplifiers also can have PA DC-to-RF power conversion efficiencies of 70% or more at the device level? In fact the solid-state, analog FM broadcast transmitters supplied by Harris Corporation and others need no tuning to produce their rated output power into a 1.3:1 SWR or less, anywhere in the FM broadcast band 88-108 MHz. Even the harmonic filter needs no changes, and maintains harmonics at -80 dBc or better. They are frequency agile, and can be reset from one carrier frequency to another, anywhere in the FM band with a transition time of a few seconds The overall AC input to r-f output efficiency of these transmitters exceeds 60% (includes the exciter, control system, IPA, and cabinet fans). RF Hello Richard, Sorry, Richard, I have no knowledge of solid-state untuned amps, so my thinking on them is zero, nada. As you'll note, all of my discussion on the subject concerns only tube amps with a pi-network output, and I've specifically stated these conditions. If you've read Chapter 19 and its addition as Chapter 19A, do you agree with my position that the output resistance at the output terminals of the pi-network is non-dissipative? Walt, W2DU |
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