Looking to see if a PT2395-based project might be viable, but from what I can tell 41256 DRAMs are obsolete. Can anyone confirm this?

Cheers

Mike

Oh, yes, long ago.

The easiest way to find 256K memory chips is to find a ...free... old computer loaded full of them.

New ones are nonexistant. Maybe some surplus houses will have some leftovers.

41256s are long gone but there were lots of them made so your chances of finding some are still pretty good if you look for places that cater to old computers (the Apple //gs used these chips quite often, they were also commonly used in 640K PC XT motherboards and expansin cards of the era.). If you can find and 256K 30 pin SIMM, there's another source.

You can also use a larger chip like a 411000 if you just tie the top address line to ground. You'll only be using 1/4 of the chip, but if it makes it work, who cares.

Hmmmmm.... looking at the datasheet it seems that you might be able to double the delay time by simply adding another 41256 and attaching the Q output of the first to the D input of the second. At worst it should take a 4013 or 74HCT74 to latch the output of the first chip for the second.

Are PT2395s still around?

Take care,
-Peter

Quote from: Peter SnowbergAre PT2395s still around?

Yes they are still in production but just alittle hard to get here in North America. I think Small Bear might have them. I know the Danelectro delay pedals are based on them.

Andrew

Excellent! Thank you.

Take care,
-Peter

similar topic:
http://diystompboxes.com/sboxforum/viewtopic.php?t=22358&highlight=  :wink:

Thankyou for the thoughtful responses. I had located some small stockpiles, but really need an ongoing reliable supply, certainly not possible it would seem without a reasonable amount of effort looking. It's possible to do a trick or two with the PT2399 to get longer delay times, but with the obvious reduction in bandwidth - for now, though, I think this will have to do. The extra R&D time spent on anything more exotic WRT memory would be unlikely recoupable for me!

Mike

PS I have some NE566s to trade with anyone who has some known working 41256s, just to indulge my interest a little .....

Very cool.

One of those PT2395s, plus a 256K 30 pin SIMM, two 74HCT04s for address buffers (if needed), and a 74HCT574 would yield a digital delay with 6.4 seconds . In addition you could make it sample and hold too with infinite repeat.

A 4046 PLL could probably get used to make a faster clock for higher fidelity or to modulate the clock!

I guess you might need a couple more NANDs or NORs, but it would be small with minimal wiring thanks to the SIMM

What about XOR mixing the repeat data with the new data? :twisted:

This seems like quite a perfect chip for a digital experimenter.

Take care,
-Peter

Mike I got all kinds of NOS Dram, I'll look and see if I got some good #'s for you if you want,
JD

QuoteOne of those PT2395s, plus a 256K 30 pin SIMM, two 74HCT04s for address buffers (if needed), and a 74HCT574 would yield a digital delay with 6.4 seconds

Is there one L or two in "PLA"?

PLA ? :?

OK, I give up... what's PLA?


Small Bear has PT2395s for $5.95 too.

Too bad the datasheet is so brief. It says 800ms in extended mode, but nothing about normal delay times. Hmmm.....

Mike, here's some #'s off the dram I got,
P21256-07,41256-12, km41256ap-12,gm71c456-10,4164-12,44256,44256-80,
that's some of the #'s, I got tube's & tube's of this stuff, if ya need any let me know.
JD

I built the app note of the PT2395 on breadboard...

Breadboard hates me...

I wasn't impressed with the quality of the delay, FWIW.

The ram I used says "MCM6256BP12"

Fp

err, wait : didn`t I soup up my old Atari ST 1040 with 16 of those chips less than 20 years ago?
If so, the Atari-DIY-scene (if it still exists) must know about sources...

:?:

One of the best sources for 41256's is in older 1meg VGA video cards, circa 1993 or so.  Some Mobo's from 1990 and earlier have them in large quantity as well.  If there are any comuter garage sales near you they'll be in abundance.

I think JD has me sorted out at the moment .... many thanks to him!

Mike

.........Mike- I just saw some for sale on Ebay........

......look for item #3821074388.......are these what your looking for?.........dr........

No, I don't believe so .... I'm after 16-pin ICs, although those *do* seem to have the 41256 code - perhaps these are 4x capacity or something? Thanks though, I'd forgot about looking on ebay, but hopefully I'm sorted for experimental purposes for the moment.

Mike

you`re not alone....  :wink: