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

[Nick Foster]

Thanks for the quick reply, John.

> From: jmfranke at cox.net
> Okay, 12V on the oscillator (pin 3) and 20V on the oven (pin 14).  How much 
> on the oven controller, pin 8?

+12V. The oscillator uses the same supply as the filter, with the addition of a 10mH inductor + decoupling caps.

> Are pins 2, 4, 5, 9, and 15 grounded?  Pin 6 (EFC) should be grounded for 
> initial testing.

Yes and yes.

Upon looking further, something jumped out at me: the output is 2.2V RMS into 1000 ohms instead of the 1V RMS spec'ed in the datasheet. So I suppose the problem might be in the AGC circuitry, instead of the output emitter follower. It doesn't look as though the AGC in this oscillator contains a trimpot, like the 10811 does.

I'm using the schematic at http://www.leapsecond.com/museum/10544/10544-3.gif, but I don't have a good idea of how that AGC works.

--n

> From: jmfranke at cox.net
> To: time-nuts at febo.com
> Date: Fri, 15 Jan 2010 15:06:42 -0500
> Subject: Re: [time-nuts] HP 10544A with dodgy output?
> 
> Okay, 12V on the oscillator (pin 3) and 20V on the oven (pin 14).  How much 
> on the oven controller, pin 8?
> Are pins 2, 4, 5, 9, and 15 grounded?  Pin 6 (EFC) should be grounded for 
> initial testing.
> 
> John  WA4WDL
> 
> --------------------------------------------------
> From: "Nick Foster" <bistromat at hotmail.com>
> Sent: Friday, January 15, 2010 2:53 PM
> To: <time-nuts at febo.com>
> Subject: [time-nuts] HP 10544A with dodgy output?
> 
> >
> > 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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