Hi all,
Prompted from my other thread in B/S/T to purchase a Nixie tube for this, here is a thread for the repair / "restoration" (might be more applicable!) of a very old Keithley Model 440 Picoammeter.
First off... I have absolutely no idea what I'm going to do with this; I only bought it for the lovely display and repair journey. So if anyone can suggest a worthy use, let me know.
The unit has cleaned up quite well so far.
Based on the now removed asset tags, it appeared to have been bought/owned by AVX Semiconductor.
Currently the "Hundreds" Nixie tube is dead. Verified by swapping the H/T/U tubes around, fault follows the tube. All drive electronics of the 3x on the card work well.
The "±" indicator works.
I currently haven't ascertained if the "1" Thousands tube works, but is not the same as the H/T/U. On my list to investigate.
The Nixie tubes are NL-841's.
It appears to be a RTS-14 base.
http://danielbriggs.co.uk/NL-841.pdfhttp://www.swissnixie.com/tubes/NL841RCA/I have a sensibly priced NOS replacement on its was from USA old aviation surplus place; it should be here in a week or so, so fingers crossed that's the glorious display back and working with the correct parts.
After then I'm swapping the mains flex as the 1970's one is breaking down / disintegrating and is bordering on dangerous.
Once the display is functional fully again I'm planning to calibrate it, and run some tiny currents through it to see what it says on each range. Any pointers? I do not have a SMU or picoampere source currently.
Now for the first batch of pics:
Note the amazing range switch and 100GΩ resistor! [I've been careful not to touch any component, as have read things that scared me like "the resistance of a fingerprint"]
Manual:
http://danielbriggs.co.uk/Keithley440.pdfWell, hope that's of interest.
All the best,
Dan