[time-nuts] HP 10811 stabilizing time

[Richard (Rick) Karlquist]

Hi Perry, I worked in the HP frequency counter section in the 1980's
when the 5335A was developed.  I was the project manager for the
5334B counter.  Basically, no counter that we ever made AFAIK had
any provision for EFC.  The basic concept is that you can get the
frequency close enough with the coarse adjust, say 1 part in 10^8.
Unfortunately, your email was garbled and we only know you were
able to adjust it to 4 to 6 parts in 10^????.  Attempting to
put in EFC would entail getting some very temperature stable
and low noise reference and some very low TC multiturn pot.
Lots of things to go wrong there.  If there was enough demand
for that feature, it is likely that HP would offered it as a
extra cost option.

If you want to add EFC yourself, it is on pin 6 of the edge
connector.  You might have to liberate that pin from ground.
The coarse adjustment is a high quality piston trimmer; no
way to do any better there.

HP was certainly not infallible, but I think you are giving
them a bum rap here.  There were many highly talented engineers
in that section (I knew them all).  The project manager of
the 5335A was eventually promoted to R&D manager and he was
the boss of the counter section manager.

Rick Karlquist
HP Santa Clara Division 1979 to 1998.

On 7/21/2019 6:53 PM, Perry Sandeen via time-nuts wrote:
> Yo Bubba Dudes!,
> I bought a HP 10811 from ebay for $36 and shipping.
> I installed it in my HP 5335a counter.  After running continuously for about 90 days it was down to about 4 to 6  parts in -10.  I couldn't adjust it for better accuracy as HP in their infinite and inscrutable wisdom provided a edge connector for the 10811 but didn't make provision for EFC one had only the course adjustment.  Sheesh!
> Now maybe I was very lucky in my ebay purchase.  On ebay prices seem to go from $125 to around $60.  One of the lower priced sellers advertise that their 10811's are *tested* but no details.
> Regards,
> Perrier
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