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Thread: Looking to buy/build a small PDP-11 system

  1. #1
    Join Date
    Oct 2011
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    Default Looking to buy/build a small PDP-11 system

    Hello all,

    I am looking to buy or build up a small PDP-11 system, something like the attached photo I stole off of someone's web site:

    20170714_101334-Large.jpg

    I'd like to hear your suggestions for what that small double wide chassis is, and where I might be able to obtain one like it. My idea is just like what is shown - to power the small chassis with a reasonable PC power supply, and add any wiring needed to create whatever "front panel" switched and indicators that may be needed.

    I figure that I can obtain a M8186, DLV11-J, 128K memory, and a disk interface on eBay, or around somewhere. That should be all that's really needed for a small system. I'd love to come across a BA11-VA, if anyone knows where one might be had for a reasonable price.

    Thanks,

    smp

  2. #2
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    Jan 2010
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    I've got a small 4-slot card rack, same as that one. It came as an embedded PDP-11/03 from a piece of Kevex lab equipment (spectrometer, IIRC). One thing you'll notice in the picture: no cooling fans! QBus boards absolutely must have forced air cooling, or you'll end up cooking at leas the CPU. They're too packed in there for convection.

    Your desired setup sounds pretty sane, make sure you get a disk controller with a boot ROM like the Emulex SCSI boards -- a dual-width CPU won't have its own boot ROM, all you'll get is ODT in microcode. Your KDF11 will top out at 128KW which is very doable on dual-width cards, but you can also plug a KDJ11 in there and find a 2MW third-party RAM board, and even run 2.11BSD. With a DLV11-J you can probably get one of the SLUs running as a SLIP line and even have TCP/IP.

    You'll also need to add a mini front panel, with at least DCOK circuitry (an AT or ATX supply provides a power good signal, I don't remember if any further conditioning is needed) and a HALT and RESET switch. Documentation exists for building one yourself.

    I could probably be convinced to part with my 4-slot QBus card cage, I keep thinking I will build a system out of it, but I keep finding that 4 slots is too small for what I usually want to do. PM me if you're interested in mine. I can provide at least a DLV11-J as well, probably the rest of the cards you need minus the disk controller, too.

  3. #3
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    Dec 2010
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    Seattle, WA
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    This page has information and pictures about setting up a small systems with a 4 slot H9281-BA card cage:

    http://home.windstream.net/engdahl/pdp-11_23.htm

    See also the section on the H9821 backplane starting on page 387 of the PDP-11 Microcomputer Interfaces Handbook 1983-84

    http://www.bitsavers.org/pdf/dec/qbu...ntrfs_1983.pdf

  4. #4

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    If you can't find one with a proper card cage, I've got a bare QBus backplane you can have for the price of shipping - I think it's four or six slots, no idea if it's 18-bit or 22-bit addressing. You would of course need to come up with a PSU. Can't remember if I have any spare cards left aside from a controller board for a mass spectrometer I don't have.
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
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    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

  5. #5
    Join Date
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    Quote Originally Posted by glitch View Post
    I've got a small 4-slot card rack, same as that one. It came as an embedded PDP-11/03 from a piece of Kevex lab equipment (spectrometer, IIRC). One thing you'll notice in the picture: no cooling fans! QBus boards absolutely must have forced air cooling, or you'll end up cooking at leas the CPU. They're too packed in there for convection.

    ...snip...
    Hi Jonathan. Thanks very much for your response. Yes, indeed, I noted the lack of cooling. I will have to implement a boxer fan or some such, right beside the card cage to assure enough air flows in between the cards.

    I've sent you a PM. Thanks very much for the possibility.

    smp
    Last edited by smp; September 29th, 2017 at 04:27 PM.

  6. #6
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    Quote Originally Posted by gslick View Post
    This page has information and pictures about setting up a small systems with a 4 slot H9281-BA card cage:

    http://home.windstream.net/engdahl/pdp-11_23.htm

    See also the section on the H9821 backplane starting on page 387 of the PDP-11 Microcomputer Interfaces Handbook 1983-84

    http://www.bitsavers.org/pdf/dec/qbu...ntrfs_1983.pdf

    Hi Glen,

    Thanks very much for those pointers. I had long ago lost track of that fellow's web site, and I'm glad to have it again. Thanks for the pointer to the DEC handbook, as well. That's one I hadn't been looking at.

    smp
    Last edited by smp; September 29th, 2017 at 04:27 PM.

  7. #7
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    Quote Originally Posted by commodorejohn View Post
    If you can't find one with a proper card cage, I've got a bare QBus backplane you can have for the price of shipping - I think it's four or six slots, no idea if it's 18-bit or 22-bit addressing. You would of course need to come up with a PSU. Can't remember if I have any spare cards left aside from a controller board for a mass spectrometer I don't have.
    Hi John,

    Thanks very much for the offer. I'll keep you in mind.

    smp

  8. #8

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    Quote Originally Posted by commodorejohn View Post
    If you can't find one with a proper card cage, I've got a bare QBus backplane you can have for the price of shipping - I think it's four or six slots, no idea if it's 18-bit or 22-bit addressing.
    You can wire-wrap the extra 4 bits on the backplane - 30-ish years ago I did that on an 11/03 backplane, as well as using a much higher wattage power supply. I had an 11/73 card in there along with a RQDX2, so as you can imagine it needed a lot more than stock power.

    I found my old write-up about this on DECUServe. Here it is:
    Quote Originally Posted by me
    Note 144.8, 5-Jun-1988
    Kennedy: Wrapping is faster!
    ----------------------------
    > For the 32 wire wraps (4X4X2) I will spring for the H9270-Q and keep the
    > old one as "spare". (about $175)

    Total effort is about 10-15 minutes to do the wrapping, compared with at
    least an equal time wrestling the backplane in & out. Not to mention that
    you can (usually) find wire-wrap wire a lot faster than a backplane!

    P.S. - If you do wrap it, do it as two vertical rows (A/B side, C/D side),
    and then connect them, rather than ABCD-ABCD-ABCD... This will reduce the
    noise. I've done this and it runs fine at 18Mhz - although the J11-RQDX2
    combo makes the 11/03 power supply scream!
    Depending on what sort of backplane you get, there may be something funky going on with the C/D slots, and dual-wide cards may only work in A/B slots. There are also a couple of obscure cards that used those 4 pins for something other than addressing. All DMA devices need to be 22-bit aware as well. If you're using a terminator board (either alone or as part of a bootstrap board) the termination needs to be 22-bit as well. But on a 4x4 backplane, you should be able to just leave the far end unterminated - there is usually another terminator on the CPU card.

  9. #9
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    I think the ultimate tiny system would be a KDJ11-A M8192 and M7195 MXV11-B. That consumes two slots. You could use emulated TU58 for mass storage, connected through the non-console SLU of the MXV11-B. If you could afford to consume a third slot, an CMD CQD-220 would allow connection of all other mass storage by SCSI. Even floppies could be connected by SCSI with the TEAC FC-1. Of course, more affordable would be RQDX3 in lieu of the CQD-220.

    I have done all these things except put them all together in a tiny backplane (I had them all in a much larger backplane.)

  10. #10
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    May 2011
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    Liverpool, England
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    I recently bought a BA11-VA and two clone BA11-VA off ebay for buttons. Only two have the four slot backplanes. I've cleaned them up and tested the PSU's. I need to acquire some boards for them now. They even have a backplate with four D25 connectors to connect to a DLV11-j4. I'd like an MXV11 but they are really expensive.

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