[time-nuts] HP 106B quartz frequency standard...the story so far

[WarrenS]

Bob

Mostly True, But
 I'd be willing to bet  there are few out there that can tell or measure the difference between the 
factory setting and the 'best' Inner oven temp setting, Especially in a relative constant Lab environment.
Unless they really know what you are doing and have the equipment & have a real goal in mind, best to leave it alone.
If it is not broken , DON'T break it.

warren

***************  
----- Original Message ----- 
From: "Bob Camp" <lists at cq.nu>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Cc: "WarrenS" <warrensjmail-one at yahoo.com>
Sent: Thursday, August 06, 2009 3:45 PM
Subject: Re: [time-nuts] HP 106B quartz frequency standard...the story so far


> Hi
> 
> Regardless of weather it's a single or double oven, you want the  
> crystal to be at it's "turn temperature". If you have a BT cut  
> crystal, that's going to be the highest frequency you find as you move  
> the oven around. With either a double or single oven, you should be  
> able to "map out" a parabolic plot of frequency versus temperature.  
> That's only close to "right" since the electronics contribute  
> something to the temperature performance. To really get it *right* you  
> need to vary the external temperature and see what happens ....
> 
> On a double oven, the outer oven is set for some "nominal" amount of  
> inner oven current. The idea is to keep the inner oven controller from  
> either cutting off or saturating as the external temperature is  
> varied. Often the inner oven is set to the "low side" of it's power  
> range.
> 
> Bob
> 
> On Aug 6, 2009, at 6:24 PM, Jim Palfreyman wrote:
> 
>> Hi All,
>>
>> Thanks very much for your interesting replies.
>>
>> I'm beginning to think I'm not letting it settle between adjustments.
>> And besides, The thing has been powered off for at least a decade I
>> would suspect and maybe I'm just watching the crystal adjust to micro
>> changes in temperature as it warms up. It's been on for about 10 days
>> with only about 30 min off time in between. I shall leave it on the
>> bench for a month or two before changing anything again.
>>
>> Now my next question is to those with double oven experience. The
>> service manual says the oven is "not field repairable". And there is
>> minimal description on how to get the oven settings right.
>>
>> The container has 61.3 C on the side - obviously the point of
>> inflection for the temperature curve of the crystal. There are two
>> test points which connect to either side of a thermistor buried deep
>> inside the inner oven. The label next to it say 432 ohms. The
>> resistance it should be at the correct temperature. I'm currently
>> running at 422 ohms (hotter) - that's the temperature that causes
>> minimal drift in frequency (at the moment - maybe this will change
>> after further burning in).
>>
>> The outer oven has no such thermistor. How do I know that is set
>> correctly? If it is too high, I'd assume it would heat the inner oven
>> too much and not allow you to drop the temperature in the inner oven.
>> If it is too low I'd guess the inner heater would have to use more
>> power and do more work to keep it ok. What is the ideal outer oven
>> temperature and how is this worked out?
>>
>> In all this, keep in mind my power rails are running a few volts high
>> and I'm not sure the effect this is having in the oven.
>>
>> Regards,
>>
>> Jim Palfreyman
>>
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>