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Thread: TV Typewriter replica project back on track

  1. #1
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    Default TV Typewriter replica project back on track

    After a whole bunch of diversions I am finally getting back to building my TV Typewriter prototype replica. Don Lancaster has been great with supplying info about the original's design. I've finally secured an MDS keypunch keyboard that is correct (keys and pattern all match that of the prototype photos, just not colour). I'm going to feel bad about disassembling a vintage piece like that, but the machine it was attached to is long gone anyway.

    I have an opinion question though: should I strive for complete accuracy and see if I can obtain photos of the prototype circuit boards somewhere and try to make the replica internals as close to the original as possible? Never seen photos of them before and not sure if whoever has it would be willing to open the original. Option B is use the plans printed in Radio Electronics. Then I could go further and socket the chips so I can swapnout quickly where they fail..

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    I would def socket the ICs no matter what!

    If you can get your hands on period - level sockets (like with machined pins) that would be even better!

    gwk

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    I think that Augat machined-pin sockets came a bit later; I do remember that most of the IC sockets found were those awful TI models--which I used in my TVT back when.

    Just wondering where all of the plain 74xx (not 74LSxx) logic came from, not to mention the old 1000 nsec. (very slow) 2102s (21L02s/91L02s came a bit later). Those 6 buggers ran very hot. The right character generator couldn't have been easy to find.

    If you're doing this thing strictly period-correct, my hat's off to you.

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    Quote Originally Posted by Chuck(G) View Post
    I think that Augat machined-pin sockets came a bit later; I do remember that most of the IC sockets found were those awful TI models--which I used in my TVT back when.

    Just wondering where all of the plain 74xx (not 74LSxx) logic came from, not to mention the old 1000 nsec. (very slow) 2102s (21L02s/91L02s came a bit later). Those 6 buggers ran very hot. The right character generator couldn't have been easy to find.

    If you're doing this thing strictly period-correct, my hat's off to you.
    Well, not 100% right off the bat, no. Some chips of the right vintages are impossible to find. The goal was to make anything I could period correct, get it running with the closest chips I could find for now and then work on finding period correct pieces.

    I have had some luck, like these char gens:

    1440023509331.jpg

    And these guys, which I think, if I'm reading date codes correctly, are 1974 or 1979 vintage:

    1440023599534.jpg

    These 7400s are 79 vintage, but they'll do I hope:

    1440023799923.jpg

    They pretty much all came from ebay. There was a chip place in California I understand closed its doors and dumped a ton of NOS and working used chips there. Still have a bunch more to get, but I'm sure I can get what I need to build it.. then just spend the rest of my days slowly accumulating correct date chips. I like neverending projects.

  5. #5
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    Quote Originally Posted by Chuck(G) View Post
    I think that Augat machined-pin sockets came a bit later; I do remember that most of the IC sockets found were those awful TI models--which I used in my TVT back when.

    Just wondering where all of the plain 74xx (not 74LSxx) logic came from, not to mention the old 1000 nsec. (very slow) 2102s (21L02s/91L02s came a bit later). Those 6 buggers ran very hot. The right character generator couldn't have been easy to find.

    If you're doing this thing strictly period-correct, my hat's off to you.
    Well. I certainly remember using the GP IC ones in the '70s, and as for machine-pin sockets in general (not IC), the tube variety has been around since the late '30s...

    BUT, my "instant-recall-memory" definitely need a trip to ReKall - ReKall - Rekall, so YMMV!

    PS : I also did a lookup in a '76 Fairchild handbook, and it lists 2102's (plain) as being 350ns (where on earth were these 1000ns chips???)
    Although my handbook (and a 1975 Intel one) only list 2102*A*, so maybe that's the difference....


    gwk
    Last edited by griffk; August 19th, 2015 at 04:28 PM.

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    I didn't think my mind was playing tricks on me--have a look at the late-1973 Intel Memory Design Handbook. PDF page 129, "Selection Guide". See the timing for the 2102? About the same speed as the 1702A EPROM. 350 mW too.

    You can see that, right about that time, where dynamic MOS shift registers looked pretty good for screen refresh. Even in 1976, the 2102-2 was 850 nsec.

    If you wanted to go fast, you could use bipolar RAM, but have a fresh supply of eggs to fry on them.

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    I just found a bunch more chips I needed on ebay, 1973 vintage (!?). The supplier (acpsurplus) seems to be dumping a lot of vintage chips on the market. I seem to recall reading around here somewhere about a major chip wholesaler or something in California going bust or shutting down, and these being the result of that? Anyone know the story? Can't find it now via search. Seems odd that they'd have 1973 NOS chips still hanging around. I got 15 or so 6540 ROMs that way. These chips are becoming a collector obsession for me all on their own.

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    This weekend I will finally begin a bit of assembly; of the case, just to have something to inspire me to keep moving forward. To match Don Lancaster's prototype, I've got what I think is the correct wood and of course just recently, the Mohawk keyboard.

    I'm currently working on a blog as I progress: http://www.bradhodge.ca/blog and welcome comments/suggestions/factual corrections. But one thing I was curious about -- did Mohawk customize their keyboards according to customers? When I was working on one of the blog posts I found a pic online of the keyboard from the first auction I missed out on, and then noticed that it was slightly different than mine. Mine has a rectangular key at the far right, and far fewer switches up top.

    Also wondering if anyone has a pic of the complete MDS key to tape system that used these keyboards. I can't find one anywhere and I've really been looking. Just curious.

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    Are you talking about the MDS 1101 system. Bitsavers has some stuff on it.

    Brochure
    Handbook

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    Thanks Chuck,

    I literally have no idea what model of system my keyboard belongs to. That's kind of the problem.. this stuff predates my existence by a few years. Just figuring out who made my keyboard was hard enough. I'll take a look at what you have there.. but unless I see a photo of the system with my actual keyboard being used with it I'll probably never know if it's correct.


    Quote Originally Posted by Chuck(G) View Post
    Are you talking about the MDS 1101 system. Bitsavers has some stuff on it.

    Brochure
    Handbook

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