Vintage Keithley Model 440 Picoammeter Repair/Restoration

[danielbriggs]

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.pdf

http://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.pdf

Well, hope that's of interest.

All the best,
Dan

[SilverSolder]

Looks in beautiful shape!  Gotta love old tech...

[Gyro]

I love the old stuff too.

Good instinct on the fingerprints, you want to keep everything in the frontend scrupulously clean.

At least it has nice cheap input connectors, not the modern Triax stuff. It looks to have a decent level of input overload protection but it would still be pretty sad to accidentally damage the matched input FETs - hopefully that calibration note on the 100pA range isn't significant and just indicates a bit of contamination somewhere.

[Ordinaryman1971]

The meter portion is the same as other Keithley multimeters... I have 160 with the same exact driver. I believe 164 has the same as seen in Marco Reps video here: