Replacement for a DEC 7474 Chip

ben bfranchuk at
Sun May 15 01:04:21 CDT 2022

On 2022-05-14 10:53 p.m., Chuck Guzis via cctalk wrote:
> On 5/14/22 15:35, dwight via cctalk wrote:
>>>> You are stuck with using an original 7474 family assuming this is driving other early TTL. 74LS74, and others simply don't have the drive capability to work.
>>> I know LS has less fanout, but is it not able to drive plain 74xx at all?  That doesn't sound right.  If the circuit in question runs near the fanout spec of plain 74 the yes, 74LS won't work.
>>> Spec sheets and the actual schematic will give a definitive answer.
> I've got a whole parts drawer full of 74S74s, which I believe exceed the
> output current capabilities of the original 7474.   There's also the
> 74ABT74, if you want a beefer BiMOS version.  Heck, I can probably come
> up with a couple of crufty old 74H74s...
> --Chuck
Faster is not better, bigger is bett... ops wrong topic.

74H while slower, and 74S tend to have reliable delay times looking at
gates with min to max delays < 3 ns. This helped devices to track
the same speed across a system.
A 74ABT00 is 1 to 4 ns depending on the temp,phase of the moon,and what 
ever. How much margin do I need to add? Ok I guess for connecting a 386?

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