Replacement for a DEC 7474 Chip

Rob Jarratt robert.jarratt at
Mon May 16 16:52:34 CDT 2022

You are right, I thought I remembered someone else saying on this thread
that he couldn't find a datasheet for the 7474 so I didn't look, but
actually I found one quite easily!


From: Paul Koning <paulkoning at> 
Sent: 16 May 2022 22:08
To: rob at; Robert Jarratt <robert.jarratt at>;
cctalk at
Cc: Rick Murphy <rick at>
Subject: Re: Replacement for a DEC 7474 Chip



On May 16, 2022, at 4:59 PM, Rob Jarratt via cctalk <cctalk at
<mailto:cctalk at> > wrote:


I have several 7474s, including one marked DEC 7474. Sadly, I fear that
shipping from the US is likely to be prohibitive.

I have ordered some 7474s. However I am getting a bit lost in the discussion
now. From a simple fan out point of view, would an S be sufficient to
replace it?


I can think of two ways to answer that: (1) ask and see if you get an
answer, hopefullly a correct one, (2) find the data sheet for the 74x74
you're looking at, and the devices it is driving, and do the calculation.
Sum up the max input currents of the driven devices, compare with the min
output current of the 74x74.  If the output current is >= the load current,
you have the needed fanout.




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