[time-nuts] HP 10811 update

[paul swed]

Rick
Thanks. But I am far simpler than that. I am trying to get the 10811 back
to 10 Mhz its -45Hz. In the long thread above I go into the troubleshooting
details so far. Because a crystal simply can't go this bad. :-) I hope not
at least.
Regards
Paul.


On Fri, Jul 26, 2013 at 1:38 PM, Rick Karlquist <richard at karlquist.com>wrote:

> Ed Palmer wrote:
> > Hi Paul,
> >
> > Did you see this page that talks about tweaking the 10811 oven
> controller?
> >
> > http://www.realhamradio.com/z3801a-turning-point.htm
> >
> > Ed
> >
>
> Although this article anecdotally claims success, it overlooks
> a number of important issues.  First of all, a large proportion
> of 10811 crystals DO NOT HAVE A TURNOVER.  They merely have a
> very low TC around 82 degrees.  It is ALWAYS 82 degrees for these
> crystals.  The crystals that do, technically, have a turnover,
> still have very low TC even if the oven is slightly off the turnover.
> Secondly, the tempco of the electronics, specifically
> the selected 2N5179 oscillator transistor, is a significant player.
> The thermal gain, if properly adjusted, is around 1000 at the
> crystal, but is much less at the oscillator transistor.  It may
> very well be the dominant factor in overall oscillator tempco.
> Possibly, if you have a crystal with a turnover, you should
> deliberately operate off the turnover at a point where the crystal
> drift cancels the drift of the electronics.
> If you want to tweak a 10811, you should also tweak the thermal
> gain by custom adjustment of the heat balancing resistors for
> the heater transistors.  This has to be done by converting the
> oscillator to mode B and then converting it back to mode C
> afterwards.
>
> Rick Karlquist N6RK
>
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