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My testing was only of the Wenzel, with a modified output transformer. I used a modified output transformer only because I did not have the components for duplicating the original design exactly. I wanted to duplicate the original design as closely as possible. My intent was to evaluate the design, and not to try to improve it.
Sorry that I misunderstood which product you performed your efficiency test on. It would really be nice to have efficiency data on the the most popular transmitters, SSTRAN and Rangemaster. You said on a thread near the end of last year that maybe Part 15 enthusiasts should concentrate on improving transmitter efficency, where some real gains could be made, and not only on antenna efficiency. To know what sort of gains could be made, we need to have data about the transmitters that are used the most.
I am not familiar with the SSTRAN, so I don’t know how to design a method for testing its efficiency. From what I have learned on the Forum, there is an impedance matching L network, and also an external loading coil. If the L network is of the capacitive input type, where the output resistance is lower than the input resistance, and the external loading coil tunes out the series-equivalent capacitance of the antenna, supplying a resistor at the output to represent the sum of the loading coil resistance and the ground resistance should be adequate. However, I have no idea if the SSTRAN circuit actually works that way.
Getting data on the Rangemaster has the additional difficulty that it costs a lot, which makes it less likely that the transmitter would be used as a test bed.
Although the Wenzel has a Class A amplifier, since the conduction angle is 360 degrees, it is not a linear amlifier, because the current approximates a square wave while the voltage is a sine wave. This causes the theoretical maximum efficiency to be higher than 50%. If both the current and voltage waveforms were sine waves, the theoretical efficiency would be 50%. Interestingly enough, if the output circuit had enough bandwidth so that both the current ant voltage waveforms were square waves, the maximum theoretical efficiency would be 100%. Actually, in this case, the theoretical efficiency could be slightly higher than 100% because of feedthrough from the driving circuit of the grounded base amplifier.