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

timeok at timeok.it timeok at timeok.it
Tue Nov 21 07:41:01 EST 2017

   Hi Charles,
   what you refer is the resistance relation referred to the LM299 source around 14VDc but you have to consider
   the tuning range of the pot, in the original HP5065A is 2E10-9.
   Of course, it depends on the setting value of the variable resistance, but you have to consider a possible variation of 20PPM/c on 2E10-9.

   Da "time-nuts" time-nuts-bounces at febo.com
   A time-nuts at febo.com
   Data Tue, 21 Nov 2017 06:31:25 -0500
   Oggetto Re: [time-nuts] HP5065A C-field mods and optical unit mods
   Luciano wrote:

   > 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.

   In the schematic Corby posted, the potentiometer (used as a variable
   resistor) makes up a very small part of the total resistance of the
   series string, so the overall tempco is dominated by the tempcos of the
   fixed resistors (2.4k to 4.4k 1ppm/ C, depending on trim). The pot will
   increase the overall tempco a little bit, but not anywhere near 20ppm.

   Best regards,


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