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
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