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 Post subject: Re: 74LS02 iCs getting scarce..
PostPosted: Sep Wed 15, 2021 8:47 pm 
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Peter Bertini wrote:
The worst chip I ever tried to locate was a 74S90N. They were made for an extremely short run. I wanted one for a homebrew frequency counter since it was about the fastest decade counter at the time... I don't see anyone selling them.

I see 74LS90 available for 86 cents at Rochester Electronics.
Is the LS a suitable substitute?

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 Post subject: Re: 74LS02 iCs getting scarce..
PostPosted: Sep Wed 15, 2021 9:32 pm 
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Pbpix wrote:
Peter Bertini wrote:
The worst chip I ever tried to locate was a 74S90N.

I see 74LS90 available for 86 cents at Rochester Electronics.
Is the LS a suitable substitute?


No, LS is too slow. S series switches faster than LS series. Did they make the 7490 in the S series ? My old TTL data books don't show such a part. The 74xx90 was an old counter. Many different counter chips came later, that do come in S series, such as the 74S162, 74S168, & 74S190. LS series had a nominal worse case propagation delay of 10nS, while S series was closer to 3nS. ~3x faster.

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 Post subject: Re: 74LS02 iCs getting scarce..
PostPosted: Sep Wed 15, 2021 9:41 pm 
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Location: Montreal, Quebec
But at the time, the S series was fastest, and if you needed it, you were willing to spend the extra current.

I don't remember a 74S90. But anything that got you faster than TTL was good. Not only would improve the upper limit of your frequency counter, but if yiu had a prescaler, it helped there.

I remember one article suggesting swapping ICs, trying to get the fastest right at the front. AndI think someone out a heatsink on a couter (thiugh maybe that was just a prescaler IC),

There were discrepancies. I remember, and used, the 74196 as a first counter in a frequency counter, for some reason it was faster. It was good up to around 50MHz, while the 7490 about 20MHz.

LS came along, and it was somewhat faster than straight ttl, and less current, but not as fast as S.

There were so many possibilities for awhile. L but that never took off, speed better than low current.


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 Post subject: Re: 74LS02 iCs getting scarce..
PostPosted: Sep Wed 15, 2021 9:46 pm 
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Location: Tehachapi, CA - Bottom end of the Sierras
Pbpix wrote:
try rochester electronics $3

https://www.rocelec.com/search?q=74ls02


Rochester comes in handy, when the have it. Reliability that the part is genuine, is somewhere between, Mouser, Digikey, etc, and someone on eBay. They sometimes get bogus parts, too.

On the note of eBay, its sometimes a valid supplier, for more common parts, where there's little incentive to counterfeit.

Though, I once got a bunch of LM358 Dual OP-Amps, that weren't as advertised. The LM358 has got to be the most bottom basement part, currently available in op-amps. Re-stamping a higher performance number (higher priced), on a lowly LM358, makes some sense. Going the other way around seems to make no sense. But that's what I got. The actual part was a lot faster, but still a "single supply" device (maybe a MC34072 ?), but re-stamped as a cheap LM358. And I got 100 of them. All shipped out, now.

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 Post subject: Re: 74LS02 iCs getting scarce..
PostPosted: Sep Thu 16, 2021 3:49 am 
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Joined: Dec Sat 28, 2019 4:18 pm
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Location: Corinth, TX
Circuit Specialists, $.60:
https://www.circuitspecialists.com/74ls ... 757ccf5b2e

John


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 Post subject: Re: 74LS02 iCs getting scarce..
PostPosted: Sep Thu 16, 2021 11:23 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Monte Vista, CO. USA
Peter Bertini wrote:
The worst chip I ever tried to locate was a 74S90N. They were made for an extremely short run. I wanted one for a homebrew frequency counter since it was about the fastest decade counter at the time... I don't see anyone selling them.

That makes me wonder: If you did come across some, would you buy them?


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 Post subject: Re: 74LS02 iCs getting scarce..
PostPosted: Sep Fri 17, 2021 2:04 pm 
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PhilF wrote:
Peter Bertini wrote:
The worst chip I ever tried to locate was a 74S90N. They were made for an extremely short run. I wanted one for a homebrew frequency counter since it was about the fastest decade counter at the time... I don't see anyone selling them.

That makes me wonder: If you did come across some, would you buy them?


LOL. That was over 50 years ago, when I had eyesight and could hand-wire a raft of chips on perfboard and come up with a useable counter for the shop. I think the 74S90 ended up being replaced with a 95H90 prescaler, so it worked out.

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