[time-nuts] HP 105B Modification

[Ed Palmer]

Bruce Griffiths wrote:
> 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.
>
...By compensating for the different output voltages of the 7474 vs. the 
74HC74.  Good point.  Which means more hacking on a perfectly good 
circuit board.  I hope I can leave this alone and duplicate John 
Ackermann's 'loose coupling' connection on the input of the 7474.  It 
should be relatively easy to duplicate the circuit on a breadboard for 
testing.

Thanks for the ideas, Bruce.

Ed

> 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