[time-nuts] HP 105B Modification

[Bruce Griffiths]

Ed

Given that the divider load current, if one substitutes a 5V CMOS 
flipflop for the 7474, only increases to about 5mA pp, using a 74HC74 is 
probably prudent given the PCB layout used, in that it may avoid EMI 
issues that may be a problem with faster logic. However it may then be 
prudent to attenuate the output of the divide by 2 fliflop to avoid 
overdriving the following emitter coupled pair.

Bruce

Ed Palmer wrote:
> The schematic is available here:  
> http://www.murgatroid.com/t_and_m/hp-00105-6100-figs.pdf .  It's also 
> available with circuit description & waveforms here:  
> http://www.kennethkuhn.com/hpmuseum/scans/hp5065a_part3.pdf on pages 
> 93-101 (pdf pages - not document pages).  However, this copy doesn't 
> show the schematic for the power supply board.  I also see that 
> document page 8-54 is missing which might be the problem.
>
> Ed
>
> Bruce Griffiths wrote:
>> If you send me the schematic for the circuit in which its used I can 
>> answer that question better.
>>
>> Bruce
>>
>> Ed Palmer wrote:
>>> Perhaps, but given what it's replacing and what it's driving, is the 
>>> difference significant?
>>>
>>> Ed
>>>
>>> Bruce Griffiths wrote:
>>>> Ed Palmer wrote:
>>>>> Yes, I have the same configuration.  The part number for the 
>>>>> divider board is 05061-6165.  The 10811 + daughter boards are used 
>>>>> in the 105B, 5061B Cesium, and the 5065A Rubidium.  The circuit 
>>>>> loading problem is exactly the kind of issue I was expecting.  
>>>>> Thanks for the warning.  I could probably resolve it by replacing 
>>>>> the existing 7474 with a 74HCT74, but I'd like to minimize the 
>>>>> amount of hacking I inflict upon the unit.
>>>>>
>>>>> Ed
>>>>>
>>>> A 74AHCT74 would be a superior replacement.
>>>>
>>>> Bruce
>
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