Eventually I found time to measure the input impedance of the amplifier. With 3 turns on the input transformer the input impedance measured 340 ohms on 80m. This is the right most curve of the three shown below - the labeling of the markers might cause confusion. With 2 turns it dropped to 159 ohms and with just a single turn it was 37 ohms.
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| Input impedance to 10W "JBOT" Amplifier |
Gain for the 10W JBOT stage has risen to 20dB with the 1 turn winding. However, I'm not completely satisfied with the "shark fin" distortion that is present on the output. Perhaps I am too picky since I have never previously looked at the output of an amplifier before any low pass filtering.
Next steps:
Add a low pass filter and measure the level of the harmonics.
If the harmonics are acceptable then I will have met my goal of a robust 10W amplifier.
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