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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Jan 15 21:39:22 UTC 2010


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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