[time-nuts] HP 10544A with dodgy output?

[Bruce Griffiths]

It sounds like the dc emitter current for the output emitter follower is 
too low.
Either that or the emitter follower transistor is faulty.

It is possible to damage the output emitter follower, it happened in one 
that I had several decades ago.
Once the output device was replaced the OCXO functioned well.

Bruce

Nick Foster wrote:
> Hi all,
>
> I've just built a GPS-disciplined oscillator built around a 10544A, somewhat in the style of the Brooks Shera unit, just to use around the shack. Problem is, now that it's wired up, I notice the output is heavily distorted. It's clipped on the negative side of the waveform, like an emitter follower without enough headroom. The more I load the oscillator output, the heavier the clipping. When I load the oscillator output with 1000 ohms, spec for this unit, almost 30% of the waveform is clipped on the negative side. If I don't load it at all and just put a probe on the output, it looks OK, but still some flattening of the bottom half of the waveform.
>
> I've got it wired up according to the datasheet, with +12V on the oscillator and +20V on the heater. The grounds for the oscillator/amplifier, oven controller, heater, and output are all tied together.
>
> I know these are old units, and I'm wondering if this is a problem (for instance in the output emitter follower amp) that others know about, before I tear into it looking for a solution.
>
> Thanks for your time,
> Nick
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