[time-nuts] HP10544A defective? Looking fro 10811

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Apr 22 10:12:20 EDT 2007

Howard W. Ashcraft wrote:
> I have been building a GPSDO around an HP10544A that I purchased on
> eBay.  After some teeth-gnashing, I have concluded that the 10544A is
> defective.  When attached to a load (it is supposed to be rated into 50
> ohms) the frequency drops radically, and in fact, the frequency is
> dependent upon load, never a good thing.  In addition, the output into a
> high impedance load has strong collateral/noise signals that are
> confusing downstream circuitry.  You can get a somewhat dirty sine wave
> if you use a high-pass filter setting on an oscilloscope.  I took a look
> on an SA and saw a fair amount of energy bouncing around 1.9 Mhz.
> I am aware of the potential interference from the switcher heating
> element and have isolated it with a LC filter, but to no avail.  Before
> I see how big a dent I can create chucking this at the wall, I thought I
> was see if anyone with experience with the 10544A thinks I'm missing
> something.  In the alternative, does anyone have a 10811 they are
> willing to sell before I start looking on eBay again?
> Thanks,
> Howard

The 10544A has an AC coupled (10nF) emitter follower output and is only 
rated for a 1000 ohm load unlike the 10811 which can drive anything from 
a short circuit to an open circuit without demur. You may have damaged 
the output transistor by trying to drive a 50 ohm load.

Can you send images of the waveform?

Despite the warnings in the data sheet it is not too difficult to repair 
the 10544 provided the crystal is OK.
However it will be easier with a circuit diagram.
Fortunately it uses 2N3904's so obtaining replacement transistors isn't 


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