[time-nuts] HP5065A C-field mods and optical unit mods

[cdelect at juno.com]

HP5065A C-field mods and optical unit mods

In addition to the power supply mods:
-removed AC components
-power now supplied with an external DC lab grade low noise 
 highly regulated supply.
-temperature coefficient of +20 Volt supply adjusted to be 
 below 1PPM/deg C
See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html


I've now installed the improved C-field circuit that has
less than +- 1PPM variation per degree C.

The optical unit has been installed into a sealed enclosure
that has been purged with dry Nitrogen. This eliminates
any Barometric pressure effects and also eliminates
drift caused by Helium permeation.

Tests at this point show a very nice long term stability.

Last mod will use a small PC closed loop liquid cooler to
keep the outside of the sealed enclosure at a constant temperature 
essentially making it a double oven.


I'm also working on:

An active temp compensation scheme to add to the
active barometric compensation I outlined earlier. 
See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html

And a passive optical unit temperature compensation using a
thermistor/resistor
arrangement.

PIX shows the sealed optical unit installed into a slightly taller
chassis. (The 5065C ?)

Cheers!

Corby
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