richard at karlquist.com
Tue Aug 17 14:40:48 EDT 2004
The E1938A was used in various HP "Smart Clocks".
The total production run of the E1938A was something
in the low 10's of thousands. It was never offered
for sale separately. I have a few dozen reject
E1938A's in my junk box. In general, they work OK,
but the crystals have frequency jumps or aging problems
that make them no better than a 10811 for timekeeping.
(I tested them all on the E1938A test system before it
It might be possible for me to make them available to
people for educational purposes only. I also have some
extra oven assemblies that can be taken apart to study
the design. I cannot accept money for them, and do not
have much time available to give "support". A number
of papers describing the oscillator are on my web site.
Brooke Clarke said:
> Hi Rick:
> Is E1938A something I could search eBay for, or are there other HP model
> numbers that encompass the E1938A?
> i.e. how to get one of these?
> Brooke Clarke, N6GCE
> Rick Karlquist wrote:
>>Brooke Clarke said:
>>>HP did quite a bit of research on isothermal oven design. The idea is
>>>that you can draw a line in three dimensional space where the
>>>temperature is constant. Since you can not have the temperature sensor
>>>and the device being controlled in the same place it's important to have
>>>them both on an isothermal line. Then the trick is to get the system
>>>gain as high as possible.
>>In the 10811, this is accomplished by ratioing the power to
>>2 heater transistors. You can tweak the ratio in an individual
>>10811 to optimize its thermal gain. A thermal gain of about 1000
>>can be achieved. The E1938A goes beyond this theory, and keeps
>>the temperature constant over a volume, not a line.
>>(See http://www.karlquist.com/oven.pdf). A thermal gain of
>>over 1,000,000 can be achieved in a single (not double) oven this
>>time-nuts mailing list
>>time-nuts at febo.com
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