[time-nuts] Simple solution for disciplining OCXO with 1 PPS

[Bruce Griffiths]

The grid current of most tubes (apart from electrometer tubes operated at low voltage) is much larger than most FETs (apart from very large area ones).. The other issue with tube grid currents is that zero current corresponds to a delicate balance between electon and ion currents so the grid current noise can be somewhat larger than one may at first expect.
Bruce
 

    On Monday, 23 May 2016 8:04 PM, David <davidwhess at gmail.com> wrote:
 

 On Sun, 22 May 2016 15:52:16 -0700, you wrote:

>...
>
>The DAC is nothing more than 16 precision resisters each
>one twice the value of the next one, each connected to one bit of the
>register by a transistor switch.

It will take beyond a heroic effort to get 16 bits of differential
non-linearity out of a binary weighted DAC.  It is difficult enough to
do with an R-2R ladder.

>I would only implement this as exercise to show how cool 1970's
>technology was.  It would be far more impressive if you limited
>yourself to 1960's technology.  I say this because one of my other
>hobbies is building tube based audio gear.  The last thing I built was
>a spring reverb, using a steel spring as the delay.    I already have
>the software version but the physical spring is more fun to use. I
>think a 60's or 70's vintage GPSDXO would be unique if strictly
>limited to period correct technology

I would not go back that far although with tube technology you do have
the capability of better than FET input impedance for long time
constants.  Chopping would be needed if offset drift below 10s of
microvolts is required.

I would like to try a mixed signal design using charge pumping into an
integrator.
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