Hi,
it is never ending story.
Currently i have some free time (i have looking for job now) so i let start to experiment with my 2dw236 diodes.
I will show you my approach to stabilisation of temperature of 2dw23x. You can see top layer PCB, U4 is ref to 2dw23x but zener is placed upside down on this two heating resistors, between them is NTC for temp. stabilisation. Between U4 and ntc, as top silk show, is placed thermal pad for better heat exchange.
On bottom side of PCB was placed 6 300R resistors for some heat up all resistors and initial heat up of U4.
Firs task was set current for U4 to achive tempco in resonable high, but not to high temp. Then i perform seting up of divider for obtain 10V on output. Lastly i have change R24 and R30 resitor to achive temp. with zero tempco of zener.
It cost me a lot of time ofcourse but i think it is possible to build some better PCB and some tester/calibrator for it. Maybe in future.
My 2DW236 have unusualy big zener voltage, something like 6.45 V even with some small current like 2 mA. If i good remember my diode work with current in between 2 mA to 3 mA.
Also power supply isn't super duper, it is ordinary transformer (230 V -> 14 V) and full bridge rectifier, then is 7815 for heaters, 33mH choke (100R, it act like fuse/current limiter btw. Removing it was a bad idea, output was noisy) and 7812 for powering OPA189.
All of this stuff was enclosed in aluminum case, with good thermal foam guled to wall although it is not hermetic.
Last question is when voltage stop dropping. This one diode is in operation since 200h in temperature close to 70 degree of Celsius.
Sincerely.