...measured values are all very close to what is stated here.
...de diode string on target (1,5 VDC)
Are you seeing 8.25mA passing through Q1,Q16,Q15 and Q6? This can be read from the voltage drop across R17 or R18.
I =E/R ?/150 should be 8.25mA. Have you considered the possibility your 500 Ohm pot is not 500 Ohms.
You can substitute the thermal track diodes with ordinary ones but it will not solve your problem.
If the voltages in red are your readings,then the voltage at Q18 collector looks to me to be too low by about 11 volts, and the voltage across the diode string should be around 2.6 volts, not 1.5.
I successfully built this using a normal Vbe mutiplier and non-thermal track devices.
I think you need to look at what is happening on the right hand side of the diode string (towards the output) As you have close to 8.25mA it seems some of this current is being shunted by a problem in the following stages.
Check that you have the correct devices in Q19,Q20,Q3 and Q1. Maybe you have swapped NPN and PNP. Measure the Vbe of these devices; it should be around 0.7V
Are you seeing 77mA through R5? E=IxR .077x16=1.232V across R5
Do you have a stereo pair of amplifiers or are you concentrating on powering up one at a time?
since I do not know how to add a .pdf-file to the answer of a PM, I will add the drill-template of my FC-100 PCB into this post.
Please compare your version of my FC-100 PCBs with the image attached:
Best regards - Rudi