2DW234 and 2DW236
I got a few 2DW236 zeners from China but the noise performance was obviously worse than the 2DW234. I notice the metal can had a different finish (matt vs bright), the part number lettering was a different font, there was no date code and on closer inspection the zener die was 0.5mm square verses rectangular with a 0.72mm length.
In the future if I have a concern about a batch of chips I will use diagonal cutters, remove the case and just look at the die. Based on my samples and other comments on this thread, the low noise chips are 0.72mm long and rectangular.
The 2DW236 sample I received were connected common anode. In a series configuration that means you will measure 0.7v on the case, pin3. The 2DW234 rectangular chips seem to be common cathode with 5-6 volts on the case, pin 3.
The 2DW236 zeners came with Factory QC paperwork also. But keep in mind they meet all the data sheet specs. It would be great if these special low noise zeners had a unique part number so they did not get mixed up with the normal 2DW23X zeners.
I'm evaluating the 2DW234 and they are very low noise. It's a challenge to measure it. I don't do the 0.1Hz to 10Hz measurements I build two identical systems and measure the difference with a nanovoltmeter. This gives a better picture of the overall worst case performance. I need to temperature regulate the parts before I will be able to get good stability numbers. Maybe I'll have that running in the next month.