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TTL for Altair Clone

Discussion in 'Electronic Basics' started by logjam, Jan 8, 2006.

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  1. logjam

    logjam Guest

    Can someone explain the main differences between those 3 families of
    logic chips?

    I read "standard TTL inputs are stable floating, will read high" and
    that "you can't substitute modern TTL families for standard and expect
    some old equipment to work"

    A project I am working on right now is duplicating an Altair 4k DRAM
    board. I'm preparing to place an order for the ICs. The manual calls
    for 74L02, 74LS00, and a 7406 (for examples). Did they choose these
    different styles (L vs. LS vs. 'nothing') because of cost or were they
    really necessary?

    The manual (link included below) is GREAT. I wish all manuals could be
    this great. :) Not really...

    For example Rev.0 of the board had a IC A, B, R as 74L04s and Rev2
    changes B to an LS04.
    Rev0 has a 7420 for J and rev2 has an L20.
    Revo has a 7400 for L and K, rev2 has a 74LS for L and a 74L00 for K.

    I suppose this could be due to wiring...

    Do I really need to be this specific when ordering new logic chips?

    I'm wondering if I need to special order these parts or if some of them
    will interchange. Will an LS part work in place of an L, or L in place
    of a 'nothing': LS work in the place of a nothing? Do you have any
    suggestions on how I could find information on these old parts?
    Searching in google only results in old stock results.

    Here are 300dpi scans of the board and a datasheet in case you are

    If you're interested in my Altair duplication project send me an e-mail
    and I'll keep you updated.

    1975 4k DRAM kit:
    Top Assembled -
    Top Bare -
    Bottom Bare -
    Manual -
  2. Mark Zenier

    Mark Zenier Guest


    That board was a notorious piece of crap.

    Nobody I knew who got one did anything besides mount it on their wall
    as a reminder to avoid repeating doing something as stupid as buying it
    and wasting their time trying to get it to work. After they replaced it
    with a nice 8K static RAM card.

    If you're looking for something cool to duplicate, try the Cromemco
    Dazzler(?) color video display board set.

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
  3. logjam

    logjam Guest

    Is that why all of mine have been gutted of their parts?

    The manual is sure pretty scary. This is Rev.2 and there are incorrect
    labels on jumpers all over the place.

    Is this 4k DRAM board decent? It doesn't look like a kit model.
  4. Rich Grise

    Rich Grise Guest

    If all he wants is a cool project, he should build a TV typewriter from
    scratch. ;-) (Admittedly, when I built mine, I had access to an EPROM
    programmer and an almost infinite supply of chips. But pipelining the
    character EPROM so it could operate at sane speeds was way kewl!)

  5. Guest

    Wow, it's been a long time since I've seen a MITS Altair memory board.
    I sort of remember that MITS had a _lot_ of problems with their early
    DRAM boards. I don't know if the board in the photo is one of the
    flakey boards. SRAM is a lot easier to work with than DRAM. I bought
    SRAM boards for my IMSAI (Altair clone) and never had memory problems.
    -Dave Pollum
  6. Lord Garth

    Lord Garth Guest

    If you like, I think I can locate the schematic of the 64k dram board I used
    in my might modify it to use 8) 64k drams rather than the
    4116 types.
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