Thanks to both Mr Simpleton and PA0PBZ !
As I am really new in this game, any advice is appreciated.
I have checked the voltages and they look quite OK
21 : 1.34 V
22 : 14.9 V
23 : 1.66 V
24 : 15. 4 V
25 : 2.79 V
26 : 19.16 V
27 : 2.35 V
28 : 2. 64 V
and across the 47 Ohms resistor : 22 V and 21.26 V
As all the voltages, and additional measures I did were looking quite reasonable, I wonder if I had put the proper frequency
for the input signal.
Indeed, It is written 39Db from 0.15 to 300 Mhz, and I had put a 10 khz signal, with the habit that this should be OK for any amplifier. But I was wrong.
When I increased the frequency in the nominal range, everything was much better, and in the nominal range.
I could try up to 30 Mhz and on the lower level up to 10 khz, but on this side, it deteriorates rapidly below 15khz.
So it seems that it is working finally. The good thing is that I have a much better idea of how it works now.