Hi Julian,
That's a kind offer, but I've already got a couple of them here. They're nice chips. One thing to watch about putting them in series: the heater supply is connected via an intrinsic diode to the zener, so you have to pay attention to where the heater supplies sit relative to the zener - to be completely safe you'd basically need 10 floating supplies, though I'm sure that could be simplified somewhat.
Alternatively, why not put them in parallel? The statistical trick should work just as well.
Bob Pease writes a bit about this here:
https://www.electronicdesign.com/arc...y-stuff-anyhow
Having summed the output, a (good!) op-amp could be used to get the voltage up to something sensible like 10V, and then you could implement your potential divider idea (and optionally, perhaps a second op-amp could buffer the output?). The op-amps mentioned in your link are promising, but from a quick look they appear to be obsolete now. I'm sure there's something else that's suitable and available. For example, the LT1001 mentioned in the LM399 datasheet is available in DIP from RS for about £4 - I've not checked the datasheet yet. The diagram towards the end of the LM399 datasheet ("Portable Calibrator") is a good starting point for this. Note the way the reference zener is supplied with the bulk of the operating current from the output (via the 5k resistor) - a good trick to improve stability in light of variations of the supply voltage.
The only downside of this approach might be the initial calibration, but you'd be welcome to visit here after the lockdown and put it on my Keithley 2015 if you can't find anyone nearer. Once done, it should be pretty stable long-term. Certainly better than the LM4040.
Anyway, that was the vague plan for mine, but other things took over. But now you've got me thinking...
