I just took Flukes oldest RefAmp, see here:

https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/msg393627/#msg393627 and modified it for 10V reference voltage.

That is, to replace the PWW 9k / 7k24 divider by 5k/10k for 10V,

and changing the other TF resistors which determine collector voltage and currents, so that these parameters stay unchanged.

This gives a similar circuit like in the 731B and 732A/B, and should behave identical, even if an SZA263 or LTFLU is used there.

Afterwards, I made slight disturbances on these 5 resistors by consecutively paralleling a 1M resistor, and then measuring the corresponding influence on the RefAmp, or the reference output voltage.

The relative decreases for each resistor was on the order of 0.15 .. 1%, and the relative changes of both voltages were attenuated, between several ppm and 3200ppm.

Dividing the relative resistor change by its corresponding relative voltage change, gives the attenuation or suppression factor for each resistor.

That means, any drift (i.e. time, temperature) of this specific resistor is attenuated by this factor.

As an example, a factor of 500 would reduce the effective T.C. of 50ppm/K for a TF resistor to 0.1ppm/K of voltage output.

This calculation was already done for the LTZ1000 circuit, which also gave attenuation factors between 75 and 700 for the different resistors.

Therefore, the 6.8V => 10V amplification resistors have to be ultra stable, as their drifts are attenuated by a factor of 3 only, whereas the other ones should also be PWW types at least, as their factors are all on the order of 170..500.

So the FLUKE type RefAmp circuit behaves - no wonder - very similar to the LTZ1000, in this aspect.

Its advantage is the direct 10V output, whereas the LTZ1000 has the advantage to deliver the raw 7.2V reference voltage as a low impedance output.

Frank