Keithley 140 DC nanovolt amplifier

Friend of mine have this interesting bit of Keithley sensitive measurement equipment legacy, Model 140 – Precision Nanovolt DC Amplifier.
It has nice analog movement with ±10 volts scale, six knobs to control various settings and typical for old Keithley large military style circular 2-pin connector.

Sadly I couldn’t find a manual for this thing online, if anyone has a copy, please scan/upload it for our collection.
Based on controls available at the front panel, we can determine some functions:

• Amplify low-level input voltages to large scale signal output (on the back)
• Has adjustable rise time, with 0.05, 0.5 and 5 seconds setting
• Has four available gain settings : 10², 10³, 10⁴ and 10⁵
• Has optional filter
• Allow to adjust zero suppression in coarse and fine steps
• Designed to operate either from AC mains or battery power (as typical for nV-stuff).

Teardown photos

There is a lot going on internally. I’ve opened up shield around business nanovolt-grade input front end for clarity.

It’s based on solid-state JFETs input stage, no tubes or lamps here.

Lot of transformers scattered around this instrument, I counted at least seven.

Missing fuse?

Not sure what’s the business here with solenoid coil. Perhaps a heavily insulated relay?

At least labels for trimpots are available on PCB board.

Output terminal is some old-school amphenol port with two terminals available.

More nanovolt input photos. Everything important has only pure copper interconnects, as expected for instrument with nanovolt in the name.

Whole box has two layers of metal shielding, µ-metal and outer steel/aluminum shielding.

Some more transformers:

Interesting test points for PCB:

All switches are electrically decoupled from the front panel knob, as expected for sensitive instrument.

Electrocube capacitor? :)

Focus-stacked photographs of the business end

I love copper unplated resistors at the front-end. Spare no expense on last tiny detail, like Keithley did.

Rotary switches also have simplistic but efficient construction. Similar to what we see in Keithley 262 divider.

If enough interest generated from this post, I might do separate tests on this Keithley 140. If you are interested and want to discuss details, you are welcome at our own IRC chat server: xdevs.com (port 4808, channel: #xDevs.com) or by reaching out to us with email.

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