[time-nuts] Making a HP 10811 better

Neville Michie namichie at gmail.com
Mon Mar 29 23:19:13 UTC 2010


I agree with leaving well alone,
But I had a HP10811 which had no EFC control.
I agonised about why this would be and bought a few varicaps,
- I could not find suitable current sources and I had resistors.
When I opened it I found the junction of the varicap diode,
the oscillator capacitor and a resistor was dry. No solder at all!
When it was soldered all worked well. Another unit was inspected and  
it had a lousy
joint in the same location. The serial numbers of the two units were  
years apart.
Now I am more confident with them I am thinking of trying to reset  
the oven temperature
to suit my ambient temperature, the aged crystal and the drift of the  
thermistor and resistors.
I may even lag the HP10811 with some insulation to reduce the  
internal temperature gradients
and reduce the oven power.
The method would be to use an external resistor which would be set to  
several likely values
increasing the temperature past maximum frequency, then the same  
values decreasing the temperature.
An hour or so at each temperature. Then a least squares regression to  
a parabola which
should show the best value.

cheers, Neville Michie





On 30/03/2010, at 9:49 AM, Mike S wrote:

> At 05:59 PM 3/29/2010, WarrenS wrote...
>
>> Bert wrote: >"would not feel comfortable tearing into the unit."
>>
>> I tend to agree, First rule is "do no harm",
>
> I've got this rule that says "If I don't know what the insides look  
> like when it's working, I won't know what to look for when it  
> breaks." :-)
>
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