[time-nuts] HP 10811A failure

Richard (Rick) Karlquist richard at karlquist.com
Sun Oct 14 16:19:58 EDT 2012

On 10/13/2012 8:30 AM, Adrian wrote:

> 12V for the oven because inside the outer oven lives a 10811-60158 ( see
> http://www.realhamradio.com/GPS-oven-journey.htm ) that, as by the specs
> sheet, is specified 12 to 30 V DC, 11 W max. at turn on (mine draws some
> 9 W), and Steady state power drops to approximately 2 W at 25°C in still
> air at 20 V (mine draws some 1.9 W at 12 V without powering the outer
> oven).

This is surprising to me.  Can you give us a citation to this spec?
AFAIK, all 10811 ovens are the same, and the ones I have looked at
sort of work at 15V, but they don't really work properly on 12V.

One source of confusion is the case of the 5334A counter.  The power
supply IMHO is poorly designed and the voltage sags down to 12V
during 10811 warm up.  (All 10811's and 10544's are guaranteed not
to draw more current than a 47 ohm resistor).  It turns out that
you can count on the 10811 oven to function sufficiently at 12V to
turn on the heater transistors and get the oven warmed up.  After
the oven warms up, the current drops back and the 5334A power supply
voltage gets back up over 20V.  This is different than saying
that it is OK to just connect a 10811 heater to a constant 12V supply.

When I was project manager of the 5334B version (a cost reduction
exercise), I took the opportunity to redesign the power supply so
that it worked correctly, in my opinion, meaning that the voltage
did not have a huge sag.  I don't like design "shenanigans".

Rick Karlquist N6RK

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