rf+tech at the pin 6 of U1 i have -2.6V.
This is good and shows that the feedback loop is regulating properly.
But, this tells me the RCA HV probe calibration may be not be good.
Since U1 pin 2 voltage is zero (returned to ground via R24), the voltage at U1 pin 3 must also be zero.
Therefore, the two currents through the resistor dividers must also sum to zero.
-1832 Volts / 29.3 MOhms = -62.5 uA, derived from the -HV
If the curent through R13 is correct, then the current through R36, R38 and R37 must also be the same magnitude, but opposite polarity. So we solve to find the total resistance required for +62.5 uA from +15 Volts:
15 Volts / 62.5 uA = 240 kOhms
The total resistance of R36, R38 and R37:
182 kOhms + 10 kOhms + 9.09 kOhms = 201 kOhms, with R38 at maximum
201 kOhms - 5 kOhms = 196 kOhms R38 mid control
Now we calculate the current from +15 Volts:
+15 Volts / 196 kOhms = +76.5 uA
This must be balanced by the same current of the opposite polarity from -HV:
-76.5 uA * 29.3 MOhms = -2242 Volts
This shows that the -HV must really be -2242 Volts and shows that the RCA HV probe cannot be trusted.