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

Nick Foster bistromat at hotmail.com
Fri Jan 15 22:37:16 UTC 2010


> Do you have the serial number of your 10544?
1244A02119


> But this would depend on if the CA3045 were used in the oscillator.

The CA3045 is only used on the buffer board. The oscillator uses several TO-5 transistors and a 2N3904.

> Is the board shown actually the oscillator board or just the buffer board?
That's the buffer + AGC board.

> Is your OCXO a 10554 or is it a 10544A?
Says 10544A on the case.

Well, after disassembly, it turns out the problem was a bad solder joint on the oscillator return wire. Sometimes you just get lucky! Everything is locked on and working now.

Thanks for everyone's help.

Nick

> Date: Sat, 16 Jan 2010 10:39:22 +1300
> From: bruce.griffiths at xtra.co.nz
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] HP 10544A with dodgy output?
> 
> Nick
> 
> The 10544A had at least 2 variants.
> I have the originals but the various datasheets are available on Didiers 
> site.
> The earlier versions had a somewhat higher phase noise spec, as can be 
> seen from the datasheets with different dates.
> There was a significant change to the circuit to achieve the lower phase 
> noise.
> 
> I don't have any details but I believe the changes were mainly to the 
> oscillator and the method of extracting the output signal from the 
> oscillator.
> 
> I suspect that using 2N3904's rather than a CA3045 may lower the close 
> in phase noise.
> But this would depend on if the CA3045 were used in the oscillator.
> Do you have the serial number of your 10544?
> 
> The circuit could be radically different as the CA3045 includes a 
> differential pair (the emitters of the pair are tied together).
>  From the image it appears that at least one of the transistors of the 
> differential pair is used in the circuit.
> Is the board shown actually the oscillator board or just the buffer board?
> 
> Is your OCXO a 10554 or is it a 10544A?
> 
> Bruce
> 
> Nick Foster wrote:
> > Bruce,
> >
> > The 10544 I have doesn't correspond to the 10544 schematic I found on leapsecond.com. Here's a photo of the AGC board inside mine:
> >
> > http://www.nerdnetworks.org/~bistromath/photos/misc/10544.JPG
> >
> > It's an RCA CA3045 array instead of the 3094's used in the schematic I saw. Looks like the best thing to do is pull it out and test it, and replace if necessary. I imagine that despite the transistor change the schematic is mostly the same. Do you happen to know for sure?
> >
> > Thanks,
> > Nick
> >
> >    
> >> Date: Sat, 16 Jan 2010 09:35:03 +1300
> >> From: bruce.griffiths at xtra.co.nz
> >> To: time-nuts at febo.com
> >> Subject: Re: [time-nuts] HP 10544A with dodgy output?
> >>
> >> The output of the diode detector is compared with the dc base voltage of
> >> the oscillator transistor adjusting the oscillator transitor current
> >> whenever the detector output deviates from
> >> Oscillator transistor base voltage - 2*Vbe.
> >>
> >> Bruce
> >>
> >> Nick Foster wrote:
> >>      
> >>> 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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