Few more photos, as promised
Top side:
Bottom side:
Modification on source PCB:
Remove R400, R401, LM399 reference.
Solder coax wire in place of LM399's diode location. This connected to Kelvin output (direct connection at LTZ's zener pins).
Solder coax wire to +15V and GND to power LTZ's opamps and control circuitry
Solder coax wire to +18.5V and power GND to provide separate current path for LTZ's heater, so it would not upset reference output.
Now, find a best spot for module location. I think it's best on bottom side, between front panel and HV Opt.002 board. It's far from mains transformer, far from pesky fan.
To have it isolated from airflow I added big piece of airlocked foam used in packing electronics.
It tied to metal chassis via dual-sided 3M tape, for better contact.
Now soldered piece of copper foil for sake of it. It's soldered to ground on power coax wire in single point. Idea to have it for even temperature distribution and bit of shielding. It's likely doing nothing at all, like audiophoolery, but hey, it's shiny and I had it without use anyway. Why not?
Piece of 4mm rubber pad is holding everything in place securely, screwed down to existing two metal stubs on chassis. Coax wires not touching anything and running at least 1cm from output wires/front panel.
Now, let's calibrate it.
Password is standard, but calibration have to be done by GPIB.
Temperature in room around +26°C. After entering calibration mode, it's just showing "Calibrating..." and output have voltage or current, which need to be measured by DMM and written back by command "CAL VALUE x.xxxxxxxx". After running all values from cal manual, it automatically saves CALRAM. Optionally you can leave a string with CALSTR "TEXT" later.
3458A was ACAL'd and initial calibration was just quick sanity check, to make sure I can get output 10.000V. I did not have too much effort on it to do.
It worked well, so I calibrated again, keeping temperature within 1°C span and measuring all at NPLC200
Result after calibration
Now I'll leave it overnight without AC, to see how good is tempco.
I checked 3458A+EDC MV106 earlier today, outputting 10VDC. That setup had
+1.23 ppm/°C tempco. I hope 3245A with LTZ + 3458A can be better.