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Thread: VC8E point plot 74xx replica

  1. #21

    Default Omnibus boards resurected

    I'd suggest an RK-8E replacement would be quite popular. There's also the RK-8L (two-board) newer design that I've seen (years ago) that never made it into production.

    A hex-wide combo KT8-A and 128KB RAM might be possible on a single board.

    If you're going to re-do the KL8-JA (M8655), might as well include the mods to allow programmable baud-rate, stop-bits, parity, etc...

    re: TD-8E. It's a real killer for system performance. Please look at whether it might be possible to create a 'TC-8E' (TC08 for Omnibus), that would be far more useful. The register display panel could be a later option.

  2. #22

    Default

    Quote Originally Posted by ftcnet View Post
    I'd suggest an RK-8E replacement would be quite popular. There's also the RK-8L (two-board) newer design that I've seen (years ago) that never made it into
    production.
    Probably quite popular yes I might need another RK8E in the future as well. But it is a 3 board set which will take a huge bit of time.
    I've seen errors in the DEC schematics from the RX8E. That is just a simple floppy controller. I've redrawn it and
    ordered the 74xx version of that board and we will see if I got those corrections right. But these errors worry me a bit.
    What can I expect from even more complicated schematics? I guess more errors...

    I have a working set of the Plessey RK8E. So if I'm crazy enough to start a redesign of the RK8E it will be
    the Plessey as reference. It depends on if other projects are successful.

    And maybe a poll would be interesting on which boards are the most desired. I have no clue
    if people here would actually build a board if they need it or just wait for stuff to pop up on Ebay.

    Quote Originally Posted by ftcnet View Post
    A hex-wide combo KT8-A and 128KB RAM might be possible on a single board.
    That should not be to difficult since there is already the 32KW RAM board. You can use that as reference.
    But it would be better to let someone else draw that since I don't have a PDP8/A. You could even put
    the bootloader in it I guess...

    Quote Originally Posted by ftcnet View Post
    If you're going to re-do the KL8-JA (M8655), might as well include the mods to allow programmable baud-rate, stop-bits, parity, etc...
    In which way do you mean programmable? I guess adding some jumpers or switches can be done.
    But software programmable would be quite useless in my opinion. It would not be compatible with original PDP8 software.
    If you want you could use this board and make your own version of it in CPLD. http://pdp8.hachti.de/projects/omni_usb/

    Quote Originally Posted by ftcnet View Post
    re: TD-8E. It's a real killer for system performance. Please look at whether it might be possible to create a 'TC-8E' (TC08 for Omnibus), that would be far more useful. The register display panel could be a later option.
    I'm very happy with my TD8E. Yes it's slow, but with a TC-8E tape controller it is still slow
    To be honest, the fact that I have a TU56 connected and working on a PDP8 is much more
    important for me then speed. And the TC-8E will take a huge amount of time.

    Talking about slow, I'm currently drawing the TA8E controller for the TU60...
    WTB: Case for Altair 8800 ...... Rolands Github projects

  3. #23

    Default

    And no one has suggested an FPP8A???
    Not so easy from the available documentation mind you, but I’d like one!

  4. #24

    Default

    After making three VC8E sets and putting online the schematics and gerbers
    there is still one thing I'm wondering...

    The VC8E seems to work fine on the internal -15V and +15V power,
    but DEC specified an external HQ power for the -15V and +15V power supply.

    Does anyone know what power supply was used originally? And does anyone have a picture of the
    original power cable? I want to specify the cable to make it as close as possible to the original.

    This is the last set I've build. I'm quite confident about the part list after soldering three sets

    VC8E M869R Front.jpg VC8E M885R Front.jpg

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  5. #25

    Default

    Well, I have a external power supply for my board. The power supply is extremely good, some where I have seen the +/-15V HQ where HQ stands for high quality. The power supply has remote sense so it can adjust the output at the far end of the cable when its loaded. I measured mine to 15,005V @ 900mA load, ~10mV ripple!

    Mine was broken, I changed the bulk capacitors and one zenerdiode to get it going. There are some pictures to look at in my (Swedish) restoration thread. To be found here: https://elektronikforumet.com/forum/...03658#p1103658

    There are pictures there where you could see the cable and the supply. Don't know the name of the supply though.

  6. #26

    Default

    Ah thanks! It's very clear to me now how it was intended.

    I had already seen that you can daisy chain the cards for the power supply.
    This HQ power is also used on the DAC and ADC boards and you
    want those stable as well if you want to do precise measurements.

    The feedback explains to me the double pinning for the GND , +15V and -15V.
    Thanks for sharing!

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  7. #27

    Default

    Well, it took some doing, but I have finally worked out what I hope is the last problem with my VC8E/M1703 space war board.

    There was a fair bit of confusion on my part about how the timers worked, but also the intensify circuit never worked to my satisfaction. (Without it, the display is really messy.) Anyway, I finally located a source for the very fast transistor in the first stage of the intensify circuit, and with that, both positive and negative going intensify are working.

    Unlike Roland's TTL clone, this is a single board, with all the logic pushed into a CPLD, and the DACs and amplifiers from the other board replaced with more modern DAC chips and op amps. I've also, at Kyle's suggestion, added RCA connectors, which make for much easier cabling than the BERG connector (though you can build it that way too, if you like).

    VC8Erework.png

    I also have EAE and non-EAE versions of space war, spacex, and other VC8E demos:
    svn co http://svn.so-much-stuff.com/svn/trunk/pdp8/src/vc8e/

    (The technology to build the serialdisk image on the fly is cool, too.)

    Vince

  8. #28

    Default

    Hi Vince, that looks great!

    I have seen a game TANK for the PDP12. I wonder is that source is available
    and if it is possible to make that work on an PDP8 / VC8E as well...

    TANK.jpg
    WTB: Case for Altair 8800 ...... Rolands Github projects

  9. #29
    Join Date
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    Location
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    Default

    Very nice Vince!
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  10. #30
    Join Date
    Mar 2004
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    Wilmette, IL (north of Chicago)
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    Sign me up please!

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