My traditional NOS sources for MK4096 have dried up, so now I have to scrounge around for “pulls” for Apple-1/Mimeo ram.
Some MITS s100 ram cards have nice Mostek MK4096 dated 1976 and early 77. Pulling chips off two MITS ram cards, out of 64 chips total... I got about 18 good ones. Don’t worry I’ll replace the ram with nice reliable MK4027 type ram not appropriate for Apple-1 but plausible for MITS since they tended to use what ever was cheapest in Albuquerque the week they were built.
How scary is that 18 chips.... pretty bad failure rate. Sure it could be that these two cards at some point were stored badly or the MITS card just kills ram chips.
Anyone else have this kind of experience with MK4096 ram chips?
Cheers,
Corey
I had good luck with a ND Nuclear Data RAM Board (board # ND-ORM 50-1089-00) with three banks of 16 Mostek MK4096N-11 with 7650 date code. All 48 tested ok.
Uh oh, is Unicorn sold out? I've been procrastinating…
I think unicorn supplies MK4027, which work fine in a Mimeo, MK4096 are more original.
Interesting. I hope not. I just ordered some and they were listed explicitly as "MK4096". At $5.99 apiece, they're certainly priced like they're the real thing.
Same for me, Unicorn sent me MK4096N-16 with date code 7726.
My experience is that you have to take some care of the cycle time. The original board uses MK4096N-11, which has a cycle time of 500 nsec, whereas the MK4096N-16 supports a slightly shorter cycle time of 450 nsec. I needed to adjust the 27K resistor at B2 down to 22K to get the MK4096N-16 reliably working. Of course also the real value of the 47pF capacitor goes into the calculation of the Apple-1 memory cycle.
He must have gotten some mk4096. Cool. Last I heard he was sending MK4027.
Ok. Update....
apparently MK4096-15 which is what MITS used on early 16k DRAM cards are not compatible with MK4096-9 or 4096-16. They are for “hobby market” and use 15V not 12v. I think they are actually MK4096-16 rejects which work at a higher voltage.
So so be careful if you are buying MK4096 chips that they aren’t the -15 version.