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

Charles Steinmetz csteinmetz at yandex.com
Tue Nov 21 06:31:25 EST 2017


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,

Charles




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