[time-nuts] HP-103AR frequency beyond adjustment

Charles Steinmetz csteinmetz at yandex.com
Thu Sep 28 08:48:17 EDT 2017

Jeremy wrote:

> The only thing I've not adjusted is the oven temperature.
> I know there's been discussion of this subject here in the
> past but my searches come up empty—I must be using the wrong keywords.
> The 103AR is just a toy for me so no harm is done if the frequency can't be
> raised to 1 MHz but if it's possible I'd like to try. Have I missed something
> somewhere?

To adjust the frequency trim range, replace selected capacitor C103 
inside the oven (nominally 18pF).  Use a C0G/NP0 ceramic.  Note that HP 
indicates this "Component [is] not separately replaceable."  But at this 
point (nearly 60 years on), opening sealed oven assemblies has become 
routine for those who maintain old HP standards.

The procedure for adjusting the oven temperature is described in 
paragraph 8-11 of the operating and service manual 01037-2 (printed Jan 
1962).  Be advised it is somewhat tedious.

If you do not have the manual, you can download it here:


Best regards,


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