[time-nuts] HP5065A C-field current is temperature sensitive

Poul-Henning Kamp phk at phk.freebsd.dk
Sat Aug 29 11:09:03 EDT 2015

In message <55E1ADA8.2000102 at arcor.de>, Adrian writes:

>Keep in mind that potentiometer R6 is one of the key components of the
>C-field circuit.
>Together with R8 and R12, it defines the reference voltage to Q6A/B.
>The tempco of that wire-wound potentiometer can certainly not be neglected.

Absolutely not, it's clearly part of the picture, but something has
10x the tempco of that one right now.

>I would suggest to check the C-field temperature dependency with an
>external precision current source feeding the C-coil directly.

That's what I'm doing right now: C-field driven by Fluke 732A
through 2.5k resistor.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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