Replacement for a DEC 7474 Chip

[Rob Jarratt]

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 comcast.net> 
Sent: 16 May 2022 22:08
To: rob at jarratt.me.uk; Robert Jarratt <robert.jarratt at ntlworld.com>;
cctalk at classiccmp.org
Cc: Rick Murphy <rick at rickmurphy.net>
Subject: Re: Replacement for a DEC 7474 Chip

 

 





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

 

              paul