One idea would be to leave the existing C-field circuit in place with a switch 
to disable it.  That'd preserve your ability to carry out the second harmonic 
adjustment procedure, while allowing you to switch back to a stable current for 
normal operation.

For that matter, it's not clear what "aging process in the A12 RVFR assembly" 
accounts for the presence of that adjustment procedure in the manual.  Given 
the absence of any other aging mechanisms other than (very) gradual lamp 
darkening, I have to wonder if the Implementers mistakenly blamed the RVFR for 
drift in some other component.  I suppose they could be referring to partial 
diffusion of the buffer gas through the cell walls... but after 40 years, is 
there any indication that this is actually an issue?

Has anyone looked into the oven temperature stability to make sure that further 
optimization of C-field stability is worthwhile?  I'm a bit behind on my email 
so this may have already come up.

-- john, KE5FX
Miles Design LLC


> -----Original Message-----
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Poul-
> Henning Kamp
> Sent: Friday, September 04, 2015 2:38 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] HP5065A C-field current voltage mod
> 
> --------
> In message <89828.1441376...@critter.freebsd.dk>, "Poul-Henning Kamp"
> writes:
> 
> >I actually have some calculations relevant to this, I'll write them
> >up on my homepage when I have a second.
> 
> Here:
> 
>       http://phk.freebsd.dk/hacks/HP5065A/20150904_math
> 
> I'd be very pleased if somebody would double-check the calculations.
> 
> --
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> p...@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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