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

timeok at timeok.it timeok at timeok.it
Fri Nov 17 10:59:25 EST 2017


   Hi Corby,


   I would first like to thank you for sharing your precious studies with us.

   I love the HP5065A because it's an extremely interesting project and I'm convinced like you we have a lot of room for improving its performance.


   *********************************
   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
   **********************************


   My approach to modifying some equipment is to try to keep it as good as possible under original conditions unless the modification leads to a substantial increase in specifications.

   For this reason I do not understand why you have removed the power transformer and its filter inductance. You could power it from the DC input and leave disconnected the AC power supply or have I missed a reason to do this?

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

   **********************************

   It would be very interesting to see the schematic of your solution. I have tested a simple ssolution replacing the R12 (333Ohms) with parallel of a 470 Ohms and a 5k Ohms NTC, this mounted in the middle of the chassis. I must admit, however, that I do not have a suitable instrumentation and a Maser reference to make appropriate measures.


   **********************************

   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.

   ***********************************

   Do you have any more detailed photographs?

   ***********************************
   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.
   *************************************

   [C:\Users\PRINCI~1\AppData\Local\Temp\msohtml1\01\clip_image001.gif]


   As you have previously written , boxing the 5065A physical module solve the problem of barometric pressure variation, making an active compensation is an alternative are you studying?


   Hope to read you soon,


   Luciano

   Timeok


   Da "time-nuts" time-nuts-bounces at febo.com
   A time-nuts at febo.com
   Cc
   Data Thu, 16 Nov 2017 12:58:13 -0800
   Oggetto [time-nuts] HP5065A C-field mods and optical unit mods
   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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