I would like to close this topic.
Replacing D27 and D28 solved the problem that the swr-power meter can now measure correctly.
This is how output power monitoring works.
I received the IRFZ24Ns I ordered yesterday.
I didn't want to change anything without them. As you can read, their existence was necessary.
I measured their characteristics with a tester (which the meter can indicate: connection of legs, input capacity and opening voltage.)
First, I measured with a used 9V battery, according to the display it was 7.1V.
Since a measurement is not a measurement, I also supplied it with 9.0V from an external power supply according to the display.
According to the measurements, I measured input capacitance between 555pF...562pF and opening voltages of 3.1...3.2V from the IOR P925 J 80 0C production product (10 pcs).
I only mention as an interesting fact that I ordered the 2N2219A from two dealers, and I measured their characteristics similarly.
There was a difference in HFE characteristics. My measurement was 163 from one dealer, and 216 from the other.
What is interesting is that the batch marking does not fit on the part from the same manufacturer, only here.
After that I returned to Sbitx.
Since the arrival of the device, I have only used it in reception, with the exception of the May 4 testing txcal artificial load transmission mode.
It was possible to short-circuit one of the FETs with a previously modified hw_settings.ini during the txcal (PSU 12.5V limited to 8 amps), so the replacement was now possible.
I soldered the FETs as shown in the picture.
I turned 'VR_bias' all the way towards the ground.
Power on: ssb mode, drive 1, mic 0 to set the quiescent current of the final stage, then reboot.
My power supply has a current monitor and current limiter, so I limited it to 2 Amps.
The quiescent current is different when receiving and transmitting.
This quiescent current taken during transmission (i.e. in the absence of an input signal) must be increased in the case of 2 FETs by 100-100 mA, i.e. 200mA (maximum 250 mA). The transmission is started by pressing PTT. There is artificial load on the output.
My further measurements show that I am satisfied with my output even without changing the original hw_settings.ini.
Measured with an external power meter at 80% drive,
80M and 40M= 35W.
30M and 20M = 20W.
17M and 15M= 15W.
12M and 10M= 10W
In short, I received a good product, except for the D28, which became the cause of all the problems.
I write this only for the edification of others. I have no hurtful intentions.
--
Gyula HA3HZ
