HP ET 5188 (in-house) Voltage Standard

[cellularmitosis]

Here's an edited version of that pdf, which just has the circuit analysis, schematic, and parts list (attached).

It looks like the main reference zener is a 1N825.

The heated reference "can" might make a great training playground for gaining experience with building and tuning an oven and current driver for the 2DW232 zeners.

[cellularmitosis]

Oh wow, hparchive has a gorgeous copy of the 6101A manual (which has the same schematic as the 6116A), which appears to have been digitally reconstructed / recreated!  Perfectly legible!

http://www.hparchive.com/Manuals/HP-6101A-Manual.pdf

I've attached a similarly condensed / edited version.

[Kleinstein]

The HP 61xx supplies use a 3 stage differential amp in the oven part. The unit shown here is just a 2 stage differential amp in the oven. Also not very many transistors outside. So the circuit seems to be even simpler, but i could very well follow the general structure.

The temperature regulation looks like a simple proportional regulator. Not sure the oven part is that good to reuse it in a more modern application. The circuit is still from the pre OP era - such circuits today are usually OP based and thus look much different. Today a transistor couple is usually more expensive than a complete OP with in many respects better performance - so precision circuits today prefer OPs over the old style pairs.

[cellularmitosis]

The circuit is still from the pre OP era - such circuits today are usually OP based and thus look much different. Today a transistor couple is usually more expensive than a complete OP with in many respects better performance - so precision circuits today prefer OPs over the old style pairs.

Thanks for your insights here.  I've been wanting to develop a better understanding of how op-amps work, so this is a useful circuit to consider.  Another thread on this forum advised studying the GAP/R P65 circuit, which was a primitive op-amp which only used 6 transistors.

[manganin]

Another thread on this forum advised studying the GAP/R P65 circuit, which was a primitive op-amp which only used 6 transistors.

It doesn't need to be that complex. See the circuit attached: 3 transistors and 3 resistors (if you replace the current sources with resistors). Works fine in applications like audio if you remember the drive capability, gain and PSRR limitations in your circuit design.

[Zucca]

cool, can't wait to see how this ends...