[time-nuts] HP 10811 update

[Rick Karlquist]

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