[WTB] Working or preferable defective nanovoltmeter

[Echo88]

Hi,

im interested in buying a working or preferably defective solid-state-nanovoltmeter like the EM N1A or Tinsley 6045. If anyone has to offer such a nanovoltmeter PM me please.

Background:

I want to build a solid-state-nanovoltmeter like the EM N1A/Tinsley 6045 or similar. The available manuals include the necessary schematics, but not the modulator front end (FETs, transformer, caps, all in a big isolated block). Therefore id like to get the infos on said front end (which FETs are used, polystyrene cap values, resistor value, winding of the transformer) and since i couldnt find those exact infos on the internet im willing to buy such a device to get the infos by disassembling it. 

Greetings,

Echo

[ap]

Why not the Keithely 155?

[azer]

Or the Keithley 181

[Kleinstein]

It does not really help of you know which polystyrene caps and JFETs are used - those caps are essential not available any more and many of the old JFETs are also not available or very expensive.

At the nV level also the layout gets really important. Not so much because of capacitance but more the thermal coupling / symmetry. Old days transformers where often some kind of permalloy. Today one could opt for less sensitive nanocrstaline material. Here it is not only the number of windings, but also about how to handle the core and avoid mechanical stress. Transformer cores might very well be custom made.

The input section might very well be all sealed or potted. So even if one has a unit there is not that much to learn from it, as taking it apart might not work. As one would use newer parts anyway, it is more learning from scratch and a few prototypes.

[Asmyldof]

You may well be more interested in reading this Linear AppNote:
http://cds.linear.com/docs/en/application-note/an159fa.pdf

And then, when you've got everything in there, feel free to read all the others as well, they are quite informative. ;-)

#Nostalgia
Remember reading the first couple in one sitting.
And then again next to the soldering iron.

I strongly suspect the cookie-tin offer still stands, even after AD acquired them.

Note:
Not saying this is what you are looking for, but it should be a good bit of inspiration for some items and may well give you an idea of some challenges you're looking at.

[Echo88]

I already am studying all documents that are available about the topic nanovolt-measurement. I know the relevant app-notes and also built my amplifier-case like the one in AN159. Both Keithley 155 (i own one) and 181 have a very high noise level in comparison with transformer-based chopper-amplifiers (old variants: Keithley 147/8). The K2182 and HP 34420A are at the moment the devices from which i mainly learn, apart from the MAT-02/MAT-03-datasheets and the respective amplifier-appnote by Mr. Rubiola (very interesting considering DC-nV-amplifiers, recommended!: http://rubiola.org/pdf-articles/conference/2004-fcs-dc-amplifier.pdf )  Also recommended: http://www.janascard.cz/PDF/Design%20of%20ultra%20low%20noise%20amplifiers.pdf

At the moment my amplifier consists of SSM2212 (MAT-02-substitute) and has RTI noise in the single digit range (BW 0.2Hz which is suitable for DC-measurement). At the moment im doing drift measurements on it and will add a autozero-feature which will cancel offset-drift, like it is done in the 34420A. Also i will lower the noise by using MAT-03 which has even lower 1/f-noise. So, i already know a bit, but want to get better in this realm by studying the best devices.

@Kleinstein: Take a look at the teardown of the N1 of the user lowimpedance. Normal polystyrene caps, FETs-part-number not visible. Might as well also be just a normal transformer core and wire from the same batch. But nobody knows because we lack the old guy with the long beard who built such things and tells us about it (like MisterDiodes with LTZ1000 or Mr. Pettis with PWWs  ) or the guy who does a whole teardown including the whole frontend and finds out its either absolutely remarkable analog-engineering like the 3458A-multi-slope-design or nothing fancy and we were just assuming.
Of course youre right with the potted front-end. But i maybe already have an option to get such a front-end in the next months. 

In the meantime i will improve my existing design and maybe also try the chopper-amp of Mr. Janasek like in the pdf above.