Here are some initial photos, as usual clickable.
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/photo/3455A/REF/heater_ctl_1.jpg)
One of benefit from old ages, is the fact that full schematics often was included in manuals. Wish today T&M vendors follow with that approach as well!
10V voltage reference circuitry:
Reference IC is custom HP 1902-0926 5-leg metal TO-99 can. It does run little warm by touch, but not nearly as hot as LM399.
Zener diode is marked on schematics 5.1V, actual measured voltage was 5.2485 VDC. Can have marking 6355 on side, can it be 55 week of 1963 ?
U2 opamp is remarked with HP part number - 1826-0059, made in HONGKONG, date code 35 week 1978.
Another opamp U3, remarked with HP P/N 1826-0009, date code 24 week 1978 is driving heater element inside VREF IC.
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/photo/3455A/REF/11177B_sch.png)
Precision resistance circuitry.
* R24 is epoxy encapsulated wire-wound 1.0020K 0.01% 1ppm/°C beast
* R21,R22,R23 are metal hermetic 0.01% 1ppm/°C resistors
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/photo/3455A/REF/11177B_sch2.png)
Close-ups:
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/photo/3455A/REF/setup_1.jpg)
Sorry for bad photos, with wires sticking around, I was desperate to try if this puppy works, so hooked it all up before taking photos. It does take some time to do proper photoshoot, and it's already late after midnight here, so will do that later.
Test setup:
* Linear transformer PSU with 7915 powering -15V input on board. Current consumption according to my Fluke 87V was ~15.8 mADC...Now it's dropped a little to 15.727 mADC as it's few degrees warmer in the room now.
* Keithley 2400 is providing +29.300 VDC and reading +15.38mADC on this rail.
* 10V output measured by
one of Keithley 2001 (roughly calibrated it myself, as my primary 2001 with Tek cal is busy at moment
gathering data from ESI DB52 bridge).
![](http://doc.xdevs.com/doc/HP_Agilent_Keysight/photo/3455A/REF/ovr_1.jpg)
Output was ~9.99975 VDC when it was powered on as is and let settle for 15 minutes. Little fiddled with R6 trimpot to set 10.000000VDC.
Now after ~1 hour 2001 showing Max: 10.000011 VDC, min voltage 9.999967 VDC.
I will compare this module to my LTZ units and my earlier LM399 10V breadboarie with K2002 to see how stable it is.
Also will compare 1Meg and 1K resistors to my custom 0.01% Vishay's.