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Thread: PDP8/F new toy, knobs wanted

  1. #1

    Thumbs up PDP8/F new toy, knobs wanted

    Today I've got a new toy, a PDP8/F. Can someone help me to get 4 orange and one yellow switch levers?
    I would love to make this machine complete again...

    IMG_20200316_010941.jpg IMG_20200316_011359.jpg IMG_20200315_201436.jpg


    This machine has a little story for me personally. Years back this was the first PDP8
    which I saw in real life here in the Netherlands. It was in a museum in Rotterdam.
    In that time they had a HUGE collection of Radio, TV, computer, calculator and maritime electronics.
    That museum is a part of a quite big radio, TV, computer and maritime shop and was started by the
    owner of the shop. He really liked old electronics and he had some volunteers to run the museum.
    Because he had a huge building he could use a big part of it for the museum.

    But that PDP8 intrigued me and I then looked for a PDP8 for myself.

    Unfortunately the owner of the shop passed away a few years back. And because of a company
    reorganization the museum had to shrink, they sold a lot of the collection.
    But last year they had to shrink a whole lot further.

    So I saved an Anita MK8 calculator, the TMC 300 BAUD modem and a Teletype 33 ASR.
    I asked about the PDP8. Noooo that one never goes away... Okay great! In my opinion it
    is way better that it is being showed in a museum then that it is hidden at someone's home...

    Then it suddenly appeared on a local trading platform for a huge amount of money which probably scared
    a lot of people away. And to be honest, this PDP8/F is just like my PDP8/M. So I didn't want to go too far.
    So I made an offer which was way lower then that they were asking. And I said if
    someone will pay more then just do it. Then the machine will have a good home too.

    After a month the ad was gone... So I asked if they did a good job on selling it.
    Well, they didn't and I could pick it up for my offer... So welcome to another 8.
    Actually the first which I've ever seen
    Last edited by Roland Huisman; March 15th, 2020 at 06:25 PM.
    WTB: Case for Altair 8800 ...... Rolands Github projects

  2. #2
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    Stay healthy and enjoy it. A good reason to stay home.

  3. #3

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    Quote Originally Posted by Roland Huisman View Post
    Today I've got a new toy, a PDP8/F. Can someone help me to get 4 orange and one yellow switch levers?
    I would love to make this machine complete again...
    I, among others, have 3D printable handle files, which gets you to functional, if not aesthetically matching results.
    (Talking folks out of their vintage stock will be harder.)

    (I also still recommend wood or plastic, not metal, to replace broken pivot axles.)

    Vince

  4. #4

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    Quote Originally Posted by jackrubin View Post
    Stay healthy and enjoy it. A good reason to stay home.
    Thanks Jack, I will enjoy it in these weird times... Also for all of you, take care!

    Quote Originally Posted by vrs42 View Post
    I, among others, have 3D printable handle files, which gets you to functional, if not aesthetically matching results. (I also still recommend wood or plastic, not metal, to replace broken pivot axles.)
    Thanks, that might be an option. Good point about that plastic replacement for the pivot axles!

    Quote Originally Posted by vrs42 View Post
    Talking folks out of their vintage stock will be harder.
    Well I might have some DEC stuff to swap. Or maybe someone
    want to swap it with a Data General Nova 3 front panel?

    DG Nova 3 front.jpg
    WTB: Case for Altair 8800 ...... Rolands Github projects

  5. #5
    Join Date
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    Quote Originally Posted by vrs42 View Post
    (I also still recommend wood or plastic, not metal, to replace broken pivot axles.)
    Vince
    Curious as to why metal would be a bad choice ?

  6. #6

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    Quote Originally Posted by jdreesen View Post
    Curious as to why metal would be a bad choice ?
    Well, the most common reason for the paddles to be lost is because they fell off after the pivot axles broke. Among paddles that are not lost, the most common failure point is the pivot axle pins. The temptation is to replace the broken pins by drilling through and inserting a steel pin, typically a bit of paper clip or the like. I think this is a mistake because the impact or shear forces on the paddle are likely to recur someday, despite our efforts to prevent that. When a paddle gets whacked, I'd like it to still be the axle protrusions that snap, rather than convey that force into the switch bodies or the switch PCB. If something breaks in there, it is much more difficult to repair.

    Vince

  7. #7

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    Quote Originally Posted by vrs42 View Post
    I, among others, have 3D printable handle files, which gets you to functional, if not aesthetically matching results.
    (Talking folks out of their vintage stock will be harder.)

    (I also still recommend wood or plastic, not metal, to replace broken pivot axles.)

    Vince
    I have seen reports of 3D printing filament made to the customers Pantone choice. I haven't ordered any so have no knowledge of how successful they are at hitting the exact shade.

    https://www.pantone.com/color-intell...-filament-line
    "It's all bits on the bus, Cowboy! It's all bits on the bus!" -- Tom Beck, #1ESS Instructor, Southern Bell Opa Locka Training Center

  8. #8

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    Quote Originally Posted by DDS View Post
    I have seen reports of 3D printing filament made to the customers Pantone choice. I haven't ordered any so have no knowledge of how successful they are at hitting the exact shade.
    I've had good results with Shapeways' sintered nylon and spray paint, which can also be color-customized.

    For that matter, I've cast decent results in two part resin. It's more difficult to color, but the color does go all the way through. I saw on the web somewhere where someone had cast a whole set of paddles for themselves.

    Dave G. even had a few injection molded sets made that were gorgeous.

    It's feasible to create a set of paddles that look OK, especially from a few feet away. What I've never seen is a set that could pass as original if you put them side by side, as you would do if you were replacing just a few paddles.

    Heck, even actual originals don't always match that well between sets. (That is not all down to ageing, either.)

    Vince

  9. #9

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    Well the PDP8/F had its ups and downs... At first I modified the power supply wiring.
    In my PDP8/M I had a fried power connector. The +5V wire was clearly overloaded.

    power fail 1 8M.jpg power fail 2 8m.jpg

    Since I have the habit to expand these machines to the max I modified the power in de PDP8/M.
    And to prevent problems in the PDP8/F I did the same in this machine. In the 8/M it was the +5V
    line which was damaged. But if this happens with the GND wire then it can be very dangerous.
    With a floating GND it is possible that the 5V for TTL chips will rise without tripping the crowbar.
    That happens when the floating GND on the backplane is pulled negative by the circuits on the -15V line.
    My solution is an extra set of wires for the GND and +5V line, soldered directly onto the power board.

    power 1.jpg power 2.jpg power 3.jpg

    After this modification you have double wires for the GND and the +5V to the backplane.

    power 4.jpg

    After running OS/8 for a half an hour it crashed. Entering a test program into the memory
    learned that the address went back to zero after entering a value in memory address 0002.
    This was caused by a broken DEC8271 on the M8300 Major Registers board. It is replaced by a
    SN74179 and the machine was back online and passed the maindecs.

    A few days ago I wanted to test my prototype VC8E controller board. But it failed the interrupt test.
    Now that was weird! But it wasn't caused by the VC8E. There was a new error in the machine.
    This time cause by a defective DEC8251 and a 74H74 on the M8330 timing generator.

    For the DEC8251 I designed a little converter PCB so you can use a SN7442 in place.
    Picture 5.jpg

    So it was back online again and the VC8E passed the tests with flying colours.

    Nice, I can put everything back together again. I moved the system a bit while it was switched off.
    And then it was POOF and dark was the house. The nut on the
    automatic mains fuse has come loose a bit. That caused the mains PCB to move and the mains
    touched the metal surface. I removed that capacitor because the leg was blown away.

    mains input.jpg

    The system is back online again. Still looking for 4 orange and one yellow switch levers.

    And in the meanwhile my VT55 broke down. These things tend to keep you busy....

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

  10. #10
    Join Date
    Nov 2014
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    Chicagoland
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    Complements on sorting out all the issues.

    Some advice with regards to the additional ground wire soldered directly to the ground plane. If there is any heating on this area (power 2.jpg), this connection may fail with time.

    My schooling on high current power supplies taught me to make sure to have a strong mechanical connection. I suggest you considering using the nearby screw on the capacitor with a crimp terminal tongue connector instead.

    Jerry

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