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Thread: What did I do to my PDP-8 today.

  1. #41

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    I have spent some time with my lab pdp-8/a lately.



    By using switching PSUs it is much lighter to carry around in the lab which is nice. But since it is an 8A100 chassis it lacks the E-connector to support hex wide core memories. I did put a 20V PSU and a -5V PSU from the very beginning so it has now become time to create that little board that should be sitting where there are two holes to the right in the chassis.

    I spent some time yesterday working on the CAD layout for the board that would hold five ECS connectors. I also included the four bank select lines to allow for 128 k memory.

  2. #42

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    Yeahh the weight of that DEC stuff... You'd better collect laptops I always use a table or chair with stuff stacked on it to get the right height. You don't want to get such a drive into the cabinet by yourself. You can't see the slides while holding a drive or pdp.

    When I got my RK05 I thought that it would be a nice place on top of the PDP8/E. And this was the easiest way to put it in the cabinet. But when I got it all in the cables of the PC04 were too short to reach the controller again. And a while later got an eye on another RK05. That one is still waiting for me to pick up. I thought that it would be nice to have them on top of each other. That meant that I had two reasons to swap the PDP8/E and the RK05...

    1.jpg 2.jpg 3.jpg 4.jpg

    But the future RK05 needs all the rack space. So the power controller and 230-115V transformer had to be moved too. So these are placed in the top of the cabinet.

    5.jpg 6.jpg

    Now I have the space for the RK05 and below that one goes the RX02 floppy drive... While placing that drive I found out that I had the wrong cabinet slides. But there is a set waiting for me

    7.jpg

    If you like to read the RK05 restoration then read this topic
    And one of my RX02 drives is here

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

  3. #43
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    Roland, I had similar problems with device locations for my 8/e. I have a DECtape rack at the top, then the TU56, the RX02, PDP-8/e, and last is the RK05. The power controller interferes with the RK05 so I will need to move it above the 8/e. I think that I have enough room for a second RK05 at the very bottom of the rack. I would like to replace the DECtape rack with a PC04, but I have never found an M840 PC8E at a price that I can afford.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  4. #44

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    Quote Originally Posted by m_thompson View Post
    ....but I have never found an M840 PC8E at a price that I can afford.
    Hmmm... Are they that expensive? I've never seen them for sale to be honest.
    It is just a single board, not a fancy three board RK8E controller...

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

  5. #45
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    Quote Originally Posted by Roland Huisman View Post
    Hmmm... Are they that expensive? I've never seen them for sale to be honest.
    It is just a single board, not a fancy three board RK8E controller...

    Regards, Roland
    We could make one, and add some other things like serial ports.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  6. #46

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    Quote Originally Posted by m_thompson View Post
    We could make one, and add some other things like serial ports.
    I have an M840 which Warren had collected along with a reader/punch. The reader punch is not in the best condition if I remember correctly.

    It is not a complicated board, it is just that they seem to be pretty rare making them apparently valuable. My suggestion would be to see if this is one of the boards that Vince has drawn up and if so have a few boards made from his work. And it doesn't look like Vince has done one of these.

    Mattis, That is a clean chassis. I do like the replacement power supplies. That must make a huge difference in weight as well as in generated heat. Are you planning on putting 128k in that machine? I think that is the only reason to populate the extra slots. I have one of the 128k boards but it does not work. The onboard power supply gets hot and does not generate the necessary voltages. There is probably a bad memory chip dragging it down and that could be a devil to find. I can always put an external power supply on it and force it to power up and see what gets hot.
    Doug Ingraham
    2nd owner of Straight 8 SN1173
    5 other PDP-8's including an 8/i and a DECSet 8000
    SOL-20

  7. #47
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    Quote Originally Posted by DougIngraham View Post
    Are you planning on putting 128k in that machine? I think that is the only reason to populate the extra slots. I have one of the 128k boards but it does not work. The onboard power supply gets hot and does not generate the necessary voltages. There is probably a bad memory chip dragging it down and that could be a devil to find. I can always put an external power supply on it and force it to power up and see what gets hot.
    Making a modern 128k memory board based on Vincent's current 32k design would be pretty easy. Finding the KT8-a memory management board for 128k will be challenging.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  8. #48

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    Quote Originally Posted by DougIngraham View Post
    My suggestion would be to see if this is one of the boards that Vince has drawn up and if so have a few boards made from his work. And it doesn't look like Vince has done one of these.
    I have taken a hint and created an Eagle CAD project for the M840 . I scanned my M840K (took me a while to figure out how to get my scanner powered up!) and loaded the photos into source control.

    Who knows when I'll find the time to draw the thing, though.

    Vince

  9. #49

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    Quote Originally Posted by m_thompson View Post
    Making a modern 128k memory board based on Vincent's current 32k design would be pretty easy. Finding the KT8-a memory management board for 128k will be challenging.
    I also thought a 128K board would be cool, and actually did a bunch of work to try and clone the KT8A. I ran into problems as there is quite a bit of logic that is actually hidden inside programmable parts. (I have no idea if I've reconstructed/second-guessed the contents of those parts correctly.)

    Vince

  10. #50

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    Quote Originally Posted by DougIngraham View Post

    Mattis, That is a clean chassis. I do like the replacement power supplies. That must make a huge difference in weight as well as in generated heat. Are you planning on putting 128k in that machine? I think that is the only reason to populate the extra slots. I have one of the 128k boards but it does not work. The onboard power supply gets hot and does not generate the necessary voltages. There is probably a bad memory chip dragging it down and that could be a devil to find. I can always put an external power supply on it and force it to power up and see what gets hot.
    I want to have a small light omnibus machine which can be used when fixing broken boards on the lab bench. Then this chassi is ideal. Horisontal mounting of boards is nice when taking measurements.

    The 8/a HEX memory boards are using -5V and +20V which are fed in on the E-slot. That is my primary reason for adding it. But why not make it identical to a real E-slot by adding the bank select signals and that strange jumper. So 128 k is not what I am aiming at.

    I want to be able to work with those core more in this lab machine.

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