I'm trying to put together a doc for University students that will give some advice on buying parts and finding datasheets. I basically want to know what differences there could be for the same part number, different manufactuers.
For the most part, things are identical. However, there are some cases where in critical designs that depend upon a specification that's pushing the envelope for the original part or for an alternate manmufacturer that was originally used, another manufacturer's part may not work. But that's more poor design when that happens.
For example a search for LM317 on
https://www.datasheetarchive.com/ returns 17 different manufacturers.
For the most part, any (for example) LM317 from a reliable, well-known manufacturer should work in any properly-designed circuit.
Are there any manufacturers to avoid. For example, I've read that you should only use NTE parts as a last resort.
I agree that NTE and other "replacement type" parts should never be specified in new designs or for published projects. That's like a manufacturer designing, building and selling a car made strictly from third-party parts bought at Auto Zone! Especially in the area of discrete parts like diodes and transistors, consider that NTE may use one of their parts to cover for the substitution of 850 different part numbers. Who's to say that NTE is going to use the same generic transistor for all of their subs for that NTE number?
That old Motorola parts are very good.
Oh, yeah? Then why did I have to replace every Motorola Nixie driver in a DMM due to failure while the drivers from NSC held up fine? I think that you can only make broad and rash statements like that if you say something like, "I've heard that Fluke's current crop of handheld DMMs are 'bulletproof'." Too many component failures are due to poor circuit design, abuse by students or the user and shouldn't necessarily be chalked up to the part or manufacturer.
If a student buys the cheapest LM317 they can find, would there be any performance or reliability issues?
Danged right! Too many "surplus" outfits sell "floor sweepings". In the old days, Poly-Paks was good at that. You end up buying a bag of what have been generically marked "LM317" or "317" -- no date code, no manufacturer's logo, none of that -- and you end up with a part that works similar to an LM317, but it doesn't meet specifications at all. For the most part, as long as the device has been purchased from a reliable source, you're going to be OK.
Do be aware that not all similar parts will work exactly the same. For instance, I made the drastic mistake of assuming that a 7400, 74LS00, 74L00, 74H00, 74S00, 74C00, 74HC00, 74ALS00 -- well, you get the picture -- all logically worked the same and only varied in specs with things like power consumption, speed, driving capabilities, etc. For the most part, that's true. But then I tried substituting a 74LS123 dual one-shot in a circuit where I'd been using a 74123 to find that it wasn't working right. After careful studying of the data sheets, I found out that the reset function is different with the two versions. So, be careful in that area of subsititution.
Dean