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

[Adrian]

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.

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

Adrian

Poul-Henning Kamp schrieb:
> Using the Fluke 732A as voltage reference improved HP5065A stability,
> but not very much, so I looked closer at the constant-current
> generator and the C-field pots "calibration":
>
> 	http://phk.freebsd.dk/hacks/HP5065A/20150828_c_pot/index.html
>
> ... and found out that the current-sensing resistors R10||R11 have
> a very high temp-co.
>
> Getting closer...
>