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

timeok at timeok.it timeok at timeok.it
Tue Nov 21 05:18:27 EST 2017

   Hi Corby,
   about the C field ten turn pot you write is a low TC pot. Normally a good Vishay  pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage reference.
   What kind of pot do you have used?

   Da "time-nuts" time-nuts-bounces at febo.com
   A time-nuts at febo.com
   Data Fri, 17 Nov 2017 12:37:57 -0800
   Oggetto [time-nuts] HP5065A C-field mods and optical unit mods

   The TX and choke and filter caps were removed as I had envisioned I would
   have to re-mount the A1 and A7 in their location.
   However with some judicious movement of the mounting holes I was able to
   squeeze them in close
   to their original spots.

   The 5065 chassis was removed and inserted into a chassis from an HP
   8405A. (just used the side panels
   and the rear panel.)

   I'll post a schematic of the new C-field supply next week. It consists of
   two LM299AH in series feeding
   a string consisting of a 2.4K, 1k, 1K and a 1K low TC pot. A switch
   allows you to short out one or both of the 1K resistors as a coarse
   adjustment. All resistor are 1PPM.

   Fixing the 20Volt and the C-field temperature contributions allowed me to
   isolate the optical units changes
   due to temp.

   The resistor thermistor combo I mentioned would be taped to the optical
   unit and compensate it only.
   It would be in series with the C-field coil.
   Not needed in my unit but thought that others might want to try it rather
   than getting as complex as I have.

   Yes the active baro and temp circuit would be an alternative for a unit
   without my mods.

   attached are PIX of the enclosed optical unit and the front panel.



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