Differences Among Keithley 610 Models

[adamredwine]

I am relatively new to electrical test equipment but I am starting a PhD in experimental physics and need to learn fast.  My advisor says he knows that the Keithley 610C electrometer will work for our needs but he sees a model 610B for sale for a good price.  He has asked me to determine if the model B would work for our needs.

Now, I don't know the exact specifications we will need but I believe we will only need to use it as an ammeter for very low currents (around 10^-13 Amps).  I have obtained specification sheets for these models but they look functionally identical with the exception of one listing offset current and the other listing grid current.

Are there any big difference between these models that I should be aware of?  Generally, what differentiates the model (other than the 'R' designation for rack form factor)?

[Kosmic]

My understanding is that the a, b and c models are revision. So they offer the same overall features but precision and accuracy was improved over time.


Personally I would try to get the later revision (610C).

[MadTux]

As I remember, the older A/B models used vacuum tube input amplifier, while C model uses FETs with isolated gate and super low gate leakage. Don't really know, which are better, vacuum tubes probably are more tolerant to abuse, while with the FET version, there are no vacuum tube related troubles.

Keithley 602 is different, in that it's battery powered. So add the price of like 10 9V batteries to your instrument and be prepared for leaked battery mess, when opening it.

[Kosmic]

There's a cheap 610C on ebay https://www.ebay.com/itm/Keithley-610C-Solid-State-Electrometer-Parts-Unit/143331467445?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

Probably need some love though.

[HighVoltage]

I had plenty of problems with "B" version and then I got a "C" version a few years ago and it has been working perfectly since I have it.  I highly recommend the 610C.
It looks like Keithley improved the over the years.
And they are really affordable these days.

[wishboneash]

I bought a dead 610A on eBay for $20. I thought I could fix it since it looked like a power supply problem. Turned out to be a blown transformer that spilled its guts. Probably due to some selenium rectifiers that failed. Most of these stacked rectifiers turned out to be bad. There was a missing connection to one of the -ve HV supplies. I am not sure how it was working before the transformer died. I had the transformer rebuilt and it now works like a charm. Except for the mirror scale on the meter which is corroded, the rest of the insides were in good condition. One of the 12AX7 tubes is weak, but that hasn't affected its accuracy at all. I like the fact it's vacuum tube based - the input stage is the last thing that will break. The input impedance on the Volts scale is 10^14 ohms which is fantastic. The resistance scale is linear which is another great feature and much easier to interpolate if you need to and can measure from 10 ohms to 10^14 ohms FS. Beats the 617 in this regard. Power consumption is a measly 40W for a tube based design. I am very impressed by this electrometer.

If anyone is interested, I put a YT video to document some of the repairs and some quick testing. Still working on better editing of my videos but hopefully informative.
https://youtu.be/TLpwEaU6wow

[Kosmic]

Was the custom transformer expensive ?

I'm a bit in the same situation where I need a custom transformer and I'm hesitating to make one myself or check for a cie that can make custom one. 

[wishboneash]

Was the custom transformer expensive ?

I'm a bit in the same situation where I need a custom transformer and I'm hesitating to make one myself or check for a cie that can make custom one. 

Is it for the Keithley 610A?. I would not call the transformer cheap ($160 I believe + s/h) but not many outfits can do this for a reasonable price for a one off order that has some unique requirements. I was more interested in bringing this thing back to life, and I thought the price for the transformer was quite fair. The transformer is not a run-of-the-mill transformer since it has all but the filament windings shielded. I got mine made at Heyboer transformers (in Michigan). There was a clown in Southern California who quoted over $400 for the same thing and would not even bother to take the specs I had worked out. He claimed he knew what I needed! Several other places wouldn't touch it or get back to me with a quote.

[Kosmic]

Was the custom transformer expensive ?

I'm a bit in the same situation where I need a custom transformer and I'm hesitating to make one myself or check for a cie that can make custom one. 

Is it for the Keithley 610A?. I would not call the transformer cheap ($160 I believe + s/h) but not many outfits can do this for a reasonable price for a one off order that has some unique requirements. I was more interested in bringing this thing back to life, and I thought the price for the transformer was quite fair. The transformer is not a run-of-the-mill transformer since it has all but the filament windings shielded. I got mine made at Heyboer transformers (in Michigan). There was a clown in Southern California who quoted over $400 for the same thing and would not even bother to take the specs I had worked out. He claimed he knew what I needed! Several other places wouldn't touch it or get back to me with a quote.

OK thanks for the info.

no it's not for a Keithley 610A. At 160$ it would definitely be cheaper to order one than make my own rig to make one.