Substitutes for the 7400 family....

How about 74HC parts ?

That's pretty much what I have been using for the last several years

boB

The hc/hct parts will be faster than the old TTLs, which could be a problem with old hairball logic.

Yes. I've had to interface new kit to very old kit. The answer was Schmitt trigger for signals coming into new, and RC filters going into old.

Joe Gwinn

You should post your specific list of wanted parts here, or on the EEVBLOG forum.

I have many 74xx parts (and 93xx too) (NOS and/or working used) that I will probably never use in a new design, and almost none of the things I repair require them either.

You might like to look at 74HCS devices. There are not a lot of them, but they do all have Schmitt trigger inputs. If you need DIL packages that might be a problem unless you make adapter boards. John

I recall some instances of people switching existing TTL designs to HC, and discovering that termination or better termination was required on clock and data lines. The RC filter should prevent that problem.

I have a box of old IC's containing a bunch of 74xx parts in original Jim- Pak or Active Electronics packaging, mostly unopened, I could send the

Glen

Thanks, but I don't need them, it was the original poster who may.

Joe Gwinn

Thanks Fred, I figured 74F should work - interesting that another poster mentioned is is essentially 74AS which widens the available sources as well.

As you say, while HC is not compatible with TTL, and HCT is 'usually', I'm looking for drop-in without having to redesign anything - these are for repairs, not new designs. Repairs need to be done on a timely fashion or customers get annoyed with really high bills for time spent on upgrades so the newer parts will work.

I do design some new simple boards and try to use modern TTL that is not being discontinued or there is a huge supply of the parts for future service.

John :-#)#

I use pretty service much the entire 74## family in my board repairs. Fixing the very first arcade games (Nutting's Computer Space) to use TTL through to modern stuff - which has other supply issues of course.

If you are willing to ship them to me, I'd be happy to refund your postage (parcel post) - my shop address is below.

Thanks!

John :-#)#

Too many problems when interfacing HC with older TTL. Both HC and HCT are essentially LS in fan-out and their output voltages don't work in a number of circuits. I was servicing one game where the board designer substituted HCT in place of the original LS and the HCT chips would not drive the optos correctly. Took a while to track that down as I had assumed the board redesign had been done correctly...

Sometimes they work, often they introduce new problems. And if one is dealing with a component level board with several issues adding a new problem to the mix isn't optimal.

John :-#(#

I would be happy to refund your postage costs! My address is in the signature...I am in Canada so postage is a bit more than within the USA.

Thanks!

John :-#)#

Dang, it says that right on the cover!

I need to RTFM obviously - COVER to cover...

John ;-#)#

That's an interesting take and valid points I'm sure.

Where I use HC parts, thare are no old TTL parts connected to the HC parts so they work fine... So far, so good anyway :)

boB

At this point I don't think I want to send you everything I have (sorry!), but if you post a list of the ones you have low stock of and which you use, then I might send you those, if I have them.

Chris

Don't make any assumptions about FAST being the same as AS. I recall they had some clear differences. Otherwise, why call it anything other than AS?