TTL Logic - 74F replace with 74LS ?

[chaoticjelly]

Hey guys,

I was wondering if it would be possible to replace TTL Logic 74F (74F251) with TTL Logic 74LS (74LS251).

I am aware that F = Fast, and LS = Low Speed.

These are the TTL Logic chips which select some of the graphics on a 6 Slot I need to fix (8 Input Multiplexer with 3-STATE outputs). I suppose that it isn't possible, but since I can't find 74F within the UK, only abroad, and 74LS are available from numerous places in the UK, it was worth asking.... long shot I know...

Cheers, CJ.

 

[channelmaniac]

Not sure on that one CJ...

I don't have the average propagation delay for signals through the F logic.

On a data sheet from TI you are looking at:

9ns average delay for 74LS
6ns for 74H
4ns for 74ALS
3ns for 74S
and around 1.7 for 74AS

I'd probably go for 74 S or AS to replace it.

I got your PM and will dig in the shop later today to see what I have. I have a ton of F series ICs and will see if I have F251s in that.

RJ

 

[ttooddddyy]

http://www.tranzistoare.ro/datasheets/70/490633_DS.pdf

Data sheet here.
They should be interchangable with no problems, although I havent tried myself.

 

[channelmaniac]

No F251s here... I have a couple of tubes of LS251s...

Still have one more box of components in storage. I'll dig 'em out tomorrow afternoon if I have time otherwise it will be Tuesday evening.

RJ

 

[Kyuusaku]

Yes you can, there's no reason to track down fast parts either.