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MicroPDP-11 - some questions

commodorejohn

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So there's been one of these hanging around at my local recycle center for a while now, and I'm thinking I may just go ahead and put in an offer on it. I'm not sure exactly which model it is. It's a bit dirty, but doesn't look battered or anything.

My questions are: A. around what would one of these be worth? I'm not looking for expert valuation, I just want to be able to counter the owner if he thinks it's worth a fortune (I'm hoping he'll only want scrap value for it, but we'll see,) and B. are there any basic tests I can do without a terminal other than plug it in and make sure smoke doesn't pour out?
 

leaknoil

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Offer him $50 for it. That's probably twice the metal value inside and doesn't take any labor. If we are talking about the pedestal like I have it's mainly just plastic. If he thinks it's worth more I'd guess he thinks its worth much more and you probably don't want to pay it. I would guess anything under $200 is a good deal if its complete.

Anything with pdp on it seems to go for silly money on ebay lately but, you very rarely see whole micropdp there so, he would have a hard time finding one to base price on. I haven't seen one for sale in at least 8 or so months. That one had like a $500 buy it now price and didn't sell instantly or anything. Had to pick it up in LA and it was a little shady looking.
 

RSX11M+

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Try to sneak a pic or two for us with your phone. There's no way to advise you without, unless you know more of what you're looking at.

Even with superficial pics, if we can't see the back and the front [preferably with plastic covers removed] it'll still be guesswork.

It would also help if we knew what you wanted to do with it, other than worship.


BTW - Don't test it there. Working systems are worth more.
 
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commodorejohn

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Hmm, good point about testing it. I don't want to do another trip just for pics, though; it's been there for a while, but I've had more than a few things that have just disappeared for scrap in between the time I visited and saw them and the time I got around to intending to buy them. When it's a PPC Mac or something that's no big deal, but these are, I 'spect, a little harder to come by.

As for the purpose, just to play around with, see what I can run on it, and so on and so forth.
 

RSX11M+

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Well, that being the case, offer what you can easily afford. I would think anything under $200 would be interesting to them, and if there's anything at all in it, it should be worth that. It wouldn't be the best deal for an empty box, but with any Hard drives, floppies, tape drives or boards, you'd be in pretty good territory. Something that's been "picked over" should be bottom dollar. Unmolested - more. There should be no "holes" in back pannels if it's "original".

Of course, if it's chock full, it could be worth much more, if things work. Still, as a play toy - you don't care what it's worth "for profit", only that it does as much for your $$ as you can get.

Don't let the opportunity to get pics pass you by, if it presents itself.

Another thought - if you've a good memory, you could try looking at some photos here on the forums to see if you recognize anything, then direct us to those posts. It's not the preferred way, but it might help.

Hmmm... sounds like we ought to have a PDP-11 Identification Article here on the forums.

... or Would that take the fun out of it??​
 

commodorejohn

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Yeah, I haven't gotten to take a good look at the machine yet. I think it's got a floppy drive and a hard disk, though. I doubt that the recycle-center staff have picked over it at all; there's only a few of them that even know from computers, and even then that's more about salvaging still-resellable PCs. The bigger danger is their scrap-happy tendencies, which is why I'm thinking I'll go ahead and see if I can't get it; if I wait, it might very well be gone.

Any good guides on model/component identification out there?

Oh, also, is the hard drive a standard MFM/RLL drive, or is it something proprietary?
 
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RSX11M+

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Most models have either writing, or an escutcheon plate on the front. The manufacture's serial number tag has a better nomenclature, but we have to look it up. [see MicroPDP 11/73]

These next comments apply to non-rack based "MicroPDP systems" since I think you would have indicated otherwise were it the case. Comments for prior E.G. - "non-Micro" systems, would be entirely different.

Drives would most likely be MFM type [not RLL], if they were DEC supplied. SCSI is another possibility, but not many were DEC sourced in PDP's but it was not uncommon to see 3rd party controllers and drives in OEM systems.

Most PDP-11's were sold as Controllers in "Expert Systems", and these tend to be the ones that lasted in service the longest, becoming available as these systems obsolesced. Examples could be Phone System Control, Bank Central Alarm Control, Radiological Measuring Devices, Nuclear Plant Control, etc. In these applications it was common for a specially suited interface card to be required in the chassis, but the bulk of the system could be all DEC. As a result these computers are often populated by a re-usable suite of DEC cards and storage.

PDP-11s were made for about 20 years, and the Micro based ones about half that time. The vast majority of the survivors will be the latter, but because they often go unrecognized (or unappreciated) - it's not unusual to hear of situations like yours where they are sold "by the pound" as scrap.

Over that time there will be some 20+ actual model variations, but fortunately for you the final 10 years will probably be limited to maybe 2 or 3 popular standalone enclosures. The BA-23 and BA-123 are the most common in "Floor Stand" form (we called them "Pedestal"). 19" Rack versions of the BA-23 and it's predecessors also exist. For RM BA-23s, the only difference is mounting hardware and cosmetics. They are easily converted.

If yours was a free-standing imitation of a very large Floor PC, then it's likely a BA-23. A quick search of the pages on this forum (or google) will result in lots of photos for you to view. If it is a BA-23, CPUs and memory for original manufacture units will be PDP-11/23, 73, 53, 83, 93 with memory sizes from 256KB to 4M and Disks from 10MB to ~250MB. But externally, they all look the same in a BA-23.

A BA-123 is the size of a small office "personal fridge" [25"H x 13"W x 28"D and up to ~130lbs] and pretty much floor standing only. [we used to say it was a nice coffee table] A BA-23 Pedestal was slimmer and deeper. While it's base was wide, requiring 10", the actual enclosure was 7"W x 25"H x 32"D weighing ~70lbs.

Not sure that helps, since you haven't described it's general size.
 
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commodorejohn

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It's pretty large, but I'm terrible with estimating sizes. From looking at the systems guide, I do think it's a BA-23 (it's certainly not 13" thick.) It doesn't seem to have the pedestal stand. If I were to guess, I'd say it's the "tabletop" model (7" thick is close to what I recall,) but of course I'm not 100% sure (did the rack-mount models have full plastic casing?) I only recall the nameplate on the front saying "MicroPDP-11," if it specified a particular model then I didn't notice it.
 

RSX11M+

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No, the plastic enclosure makes it too wide for a standard 19" rack. Tabletop may be right, but it's unusual. Might be a Pedestal with the base removed. So it was on it's side then?

If it actually says "MicroPDP-11", and the size is as you say, then you're likely correct it's a BA-23 inside.
 

commodorejohn

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Okay, it did have the plastic enclosure so it's not a rack-mount. If it was a pedestal, the base had been removed (I'm pretty sure.) It was up on end, not on its side, but this being the recycle center, that says pretty much nothing about the orientation it was actually used in...
 

leaknoil

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One important tip about dealing with recyclers or surplus places. Never ask about, or go looking for, any hard drives inside. Almost all of them have a policy of removing them. If it didn't get removed it was because they didn't know there was one inside or someone was lazy. If they find out there is one they will often not sell you the computer until its removed or rip it out right in front of you. Hard to replace sled and all.
 

commodorejohn

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My local one technically has a policy of removing hard drives, but they're rather off-and-on about actually doing it, or even considering that there is a hard drive inside if the machine's old enough. Usually it's just the newer PCs and Macs that they think to remove them from. I certainly ain't going to be bringing the matter up.
 

commodorejohn

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Well, turns out I was mistaken, and it is a pedestal-model BA-23. But I got it, for scrap value ;) The front fascia went missing, but the the front panel controls seem to be in good shape. It's got a hard drive and what the systems guide made out to be a disk drive - it's some weird thing with two flaps and a plastic bar in the middle; is it a dual drive? Do disks go on either side of the bar, between the flaps? (What kind of disks does it take, anyway? Is it a format that can be written from a PC with a 5.25" drive?)

Haven't gotten a chance to crack it open yet, but the only ports on the back besides the power connector are two DB-25 connectors (one male and one female) and one long male ribbon-cable socket (at a guess I'd say 50 pins - SCSI, maybe?) I presume the DB-25s are serial? Is it standard RS-232?
 

RSX11M+

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That was a close one... I thought you were going to miss out.


Photos before opening please. [front and rear plastic covers pull off]

Please be sure to include a legible one of the S/N tag at the rear of the metal box inside the Pedestal.

Too bad about the front cover. No chance of recovering it I suppose?

Yes - You're describing an RX-50 5.25" Dual Floppy drive.

Pictures before trying to answer more of your questions.


Oh... how much $$ ??
 

commodorejohn

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$50 (and I got a couple mini-PS/2 keyboards thrown in, because they looked handy for DOS systems ;)) Amazingly enough, the owner recognized it as a micro-minicomputer (though he thought it was an AS/400,) but didn't ask more than scrap value. I'll get photos when I get it home, though all I have is my crappy phone camera. No chance of recovering the cover, I'm afraid; I looked around for it, but it's probably already been junked. Oh well, at least they didn't trash the system itself. I just hope the hard drive didn't head-crash due to rough handling or anything.
 

RSX11M+

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Ok, thanks.

If photos are that bad, you can supplement by transcribing numbers. Just provide a photo for general location so we know what the transcribed data comes from.

Good price - BTW.

You can make a rudamentry cover if you like, but it's not required. I'll post a trace outline if you want it. Sometimes empty pedistals come up on eBay cheap enough. They ship cheap(er) because they're not heavy.
 

commodorejohn

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I think I can live without the cover, at least for the time being - the rest of the case is slightly gnarled anyway (though structurally fine,) it's not going to be a museum piece or anything. I'll get all the numbers I can.

(By the way, I've gathered that physical location of cards is important in other PDP-11 models - I'm assuming I should be taking copious notes if I disassemble it for cleaning?)
 

leaknoil

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You can make a rudamentry cover if you like, but it's not required. I'll post a trace outline if you want it. Sometimes empty pedistals come up on eBay cheap enough. They ship cheap(er) because they're not heavy.

A long time ago I needed a front plate for a VAXStation II in a pedestal stand and I tried forever to find one by begging and searching ebay daily. Never found one. They can be really hard to find. I think there are a lot more stands than face covers left in the world now.
 

leaknoil

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The pedestal is probably the easy bit to find. Its those front panels. I bet the rear cover is even harder to find. Any sysadmin I know would toss them away straight out of the box. That's just something to get in the way all the time. Just like all the faceless servers I see in scrap piles now. First thing many admin do is get rid of all that pretty plastic that looks so good on webpages but, just makes life hard.

Does the pedestal stand have an actual part listing ? If you knew what the actual part number of the face was I bet you could find one cheap from the various resellers. I'd still like to find the rear piece myself.
 
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