V7-49 electrometer produced in Minsk, Belarus.

[Kleinstein]

Connecting both meters in current mode is tricky and not measuring the real offset of the current. Both meters can have a small input voltage offset. They are not made to work with a low impedance source, but a high impedance current source.
With both meters in current mode would measure the difference in offset divided by the protection / isolation resistors of both meters. Adjusting this offset to zero would be better with a simple short than a 2 nd meter.

I know the V7-45 is using a kind of integrator, but similar to an TIA it is a relatively low impedance (may be still in the 100 M range) input. With those small currents 100 M is considered low impedance .

The more relevant test would be having the V7-49 in voltage input mode, which I assume the meter would also support.

[Kleinstein]

The meters do have an offset, the troublesome point is the offset voltage. If one connects a resistor of let's say 10 M from ground to the input of a TIA / integrator type amp-meter it would read a  different current from the open circuit case. This is due to the internal offset voltage. I don't know how much this would be with the vibrating capacitor, but there is a good chance to have some 10 µV, possibly more.

Turning off the feedback at the V7-49 is kind of setting the meter to voltage mode, though the 2nd OP may still run into saturation. Because it is separate from the input stage it would still no effect the input current.
The output of the program 10 should ideally be the voltage. So the V49 would read the offset voltage of the V45 + it's own offset voltage and the V45 would read the bias current of the V49 (ADA4530) + it's own bias current (rather small).

[bsw_m]

Historical information.
I'm found price for this electrometer in 1990 year: 2975 rubles.
The official exchange rate in the USSR was 1.64 USD per ruble.
So this device cost $4879 in 1990.

[exe]

So this device cost $4879 in 1990.

Wow, that's a lot of money... Well, makes sense, I just expected it to be much more... affordable.

[bsw_m]

I did a home metrology check on my B7-49. The results can be found in the attached file.

[bsw_m]

This device has a strange GPIB, I had to spend a lot of time to get the device to work smoothly via GPIB.
As result I'm share dirty, but smoothly working code for using this electrometer over GPIB.

[bsw_m]

Little and may be last upgrade to my V7-49.
New full custom display with backlight from the daughter of MNIPI: unitary enterprise "Display"

[harrimansat]

accepted !

Is that a KPC104A with Voskhod/Kaluga logo?
Who has datasheet? Generic FET or secret weapon component from cold war?

(Saving part number on ebay in case it someday it pops there.)

Here i

Can you please share datasheet again?   I have two of these pair fets

[bsw_m]

Can you please share datasheet again?