[volt-nuts] Fluke 720A Kelvin Varley Divider Questions

[Greg Burnett]

Bruce wrote:

A more general question would be:

Is it possible to design a chopper stabilised null detector using modern
components with a performance equivalent to the 845A?

Whilst the noise of most chopper stabilised opamps is much larger than
that of the 845A, perhaps something like the approach used in:
http://cds.linear.com/docs/LT%20Magazine/LTMag-V16N01-11-FETAmp-Williams.pdf
could be used.

Since the low noise preamp is AC coupled a lower noise input using a
single ended JFET could be substituted for the one using the LSK389.

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Good question/suggestion Bruce.

Maybe that approach could be used to re-design the first "half" of a HP 
419A, building a modern circuit into an existing HP 419A to save time/money 
and to come up with a nice little box that works well. (The HP 419A *was* a 
small form-factor, cute, attractive instrument, with built-in supply & 
batteries, so it might yet still have a use?)

I think the 419A can be purchased for practically nothing, if it can still 
be found. ...again, I'm afraid many of them have already gone to graveyards 
for scrap metal recovery.

Greg