This picture shows the amplifier.
It is not 100% the same as the SM0VPO amplifier.
I did not use a thermistor in the the bias current regulator. When I find a 1K thermistor I will add it. Now I just use a 1 K resistor. The bias circuit for the driver is different too. I don't remember why I changed that.
The amplifier works but I can only get 5 watt output. I add a few capacitor to smoothen the base and the collector voltages. They are sinus shaped now. Without those capacitors the signals cointains spikes.
A problem is that collector voltages reach their maximum at 7 Watt. That should not happen. I tried different ouput transformers but the results are the same. The output voltages divided by the input volatges just doesn't match the turn ratio. Input current of the finals is 1.5 Ampere for 5 watt output, so the efficiency is low too.
I will have to investigate what is wrong meanwhile I keep using amplifier as it is stable. I did not see it oscillate, even when SWR was high. The output looks clean.
Then I checked the audio. It souns good on a shortwave receiver.
Next task is to improve power and efficiency and build a lowpass filter.
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