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

[John Ackermann N8UR]

Attached is a frequency plot of my 5065A vs. GPS (via PPS) over about 6 
months.  Note the changed freq and slope between about MJD 57205 and 
57235.  That correlates to the month we were out of town on vacation, 
with the air conditioning set about 6 degrees higher than normal. 
(There was probably less differential than that in the basement lab vs. 
the thermostat upstairs, so don't try to do any absolute measurements 
from this.)

On 08/31/2015 02:32 AM, Poul-Henning Kamp wrote:
> --------
> In message <A1A54F1F-926F-42A9-8AEC-F83BCAF4E58D at n1k.org>, Bob Camp writes:
>
>> As we go joyously bashing the poor guys that designed this beast,
>> it’s worth noting just how old the design is. 741 op amps were
>> indeed “modern” [...]
>
> I don't think chip op-amps appear until the 5065 is a toddler, later
> revs use a couple of them.
>
> The only thing I feel like beating them up about, is that appearantly
> they didn't consider the tempco of the R10||R11 pair (or maybe it is
> just R10 - not sure yet).
>
> Either way:  If any of you have a non-amazing HP5065, Measure the
> A15CR5 voltage, multiply it by 76, and replace R10||R11 with something
> of that value and better than 5PPM tempco.
>
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