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Weird PDP-8A

Q

Qbus

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Joined
Feb 23, 2011
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Location
Salisbury Maryland
Although I have seen most of the PDP-11 family and some of the 8 family don’t recognize this thing, EBay item # 201027722352 says it’s a PDP-8A but some of the internal cards look like they belong to a Unibus system, most PDP-8 systems I have seen only accommodate signal and quad cards. What’s with the six slot cards that appear to be in this? Was this a PDP-8A that was intended to be used for large systems with lots of drives or other items?

Qbus
 
Qbus said:
Although I have seen most of the PDP-11 family and some of the 8 family don’t recognize this thing, EBay item # 201027722352 says it’s a PDP-8A but some of the internal cards look like they belong to a Unibus system, most PDP-8 systems I have seen only accommodate signal and quad cards. What’s with the six slot cards that appear to be in this? Was this a PDP-8A that was intended to be used for large systems with lots of drives or other items?
Qbus
Click to expand...
The 8a used some hex wide cards, CPU, interface, memory. Unless it used the 8e CPU. And the RL8a was hex wide too. This is a real pdp-8a. Still not sure how
to figure out what the yellow tabbed cards do as they don't seem to be documented well.
 
I asked the seller about any other DEC hardware he might have. After all, I need to know whether I want to bid on the PDP-8/M or hold out for something like an 8/E with a larger backplane. He said that all of his hardware is related to the PDP-8/A, /E, /F and /M but hasn't provided other details to me yet. He also said that he has some non-DEC Sykes TT100 cassette drives that were used with PDP-8 machines, and that they're quite large. I don't recognize that model. And he says he has an ASR 33.

My PDP-11/44 project is only going to fill a little over half of the 42U rack I got for it… Maybe a PDP-8 system ought to live in the upper floors?
 
NF6X said:
I asked the seller about any other DEC hardware he might have. After all, I need to know whether I want to bid on the PDP-8/M or hold out for something like an 8/E with a larger backplane. He said that all of his hardware is related to the PDP-8/A, /E, /F and /M but hasn't provided other details to me yet. He also said that he has some non-DEC Sykes TT100 cassette drives that were used with PDP-8 machines, and that they're quite large. I don't recognize that model. And he says he has an ASR 33.

My PDP-11/44 project is only going to fill a little over half of the 42U rack I got for it… Maybe a PDP-8 system ought to live in the upper floors?
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Even with the RL02s?

I don't know what Sykes TT100's are besides what you said. I never had an 8a till much later and both are long gone too.

I wish I had kept my ASR-33.
 
tradde said:
Even with the RL02s?
Click to expand...

I'm presently only planning to install two of the RL02 drives in the rack, at 6U each. Then the Kennedy 9610 tape drive at 5U, and the PDP-11/44 at 6U, for a total of 23U (possibly plus another U or three if I have to kludge slides and something doesn't line up right). So that leaves up to 19U for something else, limited by fear of the whole mess filling through the floor of my manufactured home.

tradde said:
I wish I had kept my ASR-33.
Click to expand...

Me, too! I got mine free off a junk pile back in college. One with stand and copyholder, one without. Then I gave them away to a couple of Canadian guys for their PDP-8 restoration back in the late 90s or so, IIRC. I just replaced them with an eBay purchase, and I must shamefully admit that I helped prop up the absurd pricing of such things on eBay of late. But it came with the chad bucket! The print hammer is presently soaking in a beaker of WD40 on my workbench to see if that softens up the remnants of the rubber pad to make them easier to remove. The hammer is down to the metal, so at the very least I'll try replacing the pad with a Bumpon. A proper new pad that snaps over the rivet like the original would be nicer, but I don't know how to make rubber moldings like that. I'll be worried about the Bumpon flying off during printing such that the hammer ruins the print drum before I notice the problem.
 
NF6X said:
I'm presently only planning to install two of the RL02 drives in the rack, at 6U each. Then the Kennedy 9610 tape drive at 5U, and the PDP-11/44 at 6U, for a total of 23U (possibly plus another U or three if I have to kludge slides and something doesn't line up right). So that leaves up to 19U for something else, limited by fear of the whole mess filling through the floor of my manufactured home.

Me, too! I got mine free off a junk pile back in college. One with stand and copyholder, one without. Then I gave them away to a couple of Canadian guys for their PDP-8 restoration back in the late 90s or so, IIRC.
Click to expand...
I bought mine back when I had an Altair 8800. I didn't pay a ton but it was in
pristine shape. I thought I was done with the amatuer computers so gave it to a friend. Doh. Oh well.

I had a full 8e racked with 2 RK05s and quite full 8e. I tried to keep it along an outside wall for better joist support. The 8i
was the one I worried about. 4 racks and extermely heavy. Lucky my basement had an I-beam running the lenght so
I kept it close to the inner wall over that. You should probably be fine. Put a board down under it to distribute weight better.
 
I'll put it near the external wall so it's close to the perimeter foundation. The floor joists are steel, so that's a plus.

It'll be cool if I can find something like a PDP-8/E, DECtape drive, and RK05 to rack up above the PDP-11. But if either one grows much, then I might need a second rack.
 
NF6X said:
I'll put it near the external wall so it's close to the perimeter foundation. The floor joists are steel, so that's a plus.

It'll be cool if I can find something like a PDP-8/E, DECtape drive, and RK05 to rack up above the PDP-11. But if either one grows much, then I might need a second rack.
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I had a TC08 for the 8i. I tried to use it with the 8e once. You need special cables which I still have to connect it. If you find
yourself in that boat drop me a line. I was lucky years ago when a college in Pa was relocating their dept and I got a bunch
of racks and all the RL02s and packs I could take in my truck. All that's long gone to others now. Lou got a ton of stuff
from me when I moved. If you find that system at a reasonable price then you are one lucky guy. Right now I'd not
mind finding just an 8e again. I prefer the 8e since it has dual backplanes, but would not turn down an 8f or 8m.
 
My workshop is at grade level with a concrete floor, between the computers and radio stuff needed heavy duty floor. Also have separate electrical panel in shop for dedicated 120 and 240 volt distribution. Too bad cant get three phases! But don’t matter however much space you have it will fill up but the eight hardware just looks like it always takes twice the space of the eleven stuff. Had a RK drive a while back that I sold to someone doing an eight and it was close to two hundred pounds when ready to ship. Good luck with the sale; I will stick with the eleven family and lighter accessories.
 
Mark,

On that 11/44 system you will eventually want an RX01 or RX02, so save room for that. I think you should put your future pdp-8 system in it's own rack.

RK05s are not going to be happy high up in a rack. They are so heavy that they must be at the bottom.

Lou
 
Ok, makes sense. Speaking of RX01/RX02, I have one of the Lotharek floppy drive emulators on the way from eBay. I've read reports of some success using it in 8" applications. I wonder if anybody has tried using one to emulate an RX01 or RX02 before? Do the drives use something near the "common" 8" drive pinout? I haven't gotten around to studying those maintenance prints yet.
 
The real dec RX01 and RX02 drive interfaces are nothing like the SA800 (otherwise usual 8") or SA400 (otherwise usual 5-1/4") drive interface. However, there are non-dec work-alike RX01/02 interfaces for connecting an SA800 to an 11. I have such a device from MTI for the qbus, and there must have been unibus versions. Something like that may work with the HxC2001 based emulators (like the one you just bought.)

Lou
 
Cool. Thanks!

Yes, I do want an RX01 and/or RX02 for the system. I also hope to find a TU58-CA, even though I'm working on a little TU58 emulator project to emulate the drive without being tethered to another computer.
 
Why not just put the TU58EM software emulator on a BeagleBoard or RaspberryPI? They should certainly be capable of running it without issue, and are small enough and low power.

Personally I like using TU58EM running off the same PC I'm using as the console terminal, so don't see a real need for a separate standalone hardware box. But I guess if someone is using a real terminal instead for the console it might be more convenient.

Don
 
A Beagle or RasPi would run an emulator just fine, but I have an interesting form factor in mind for my little project. I'll spill the beans eventually, but for now I'm keeping it under my hat until it's further along.

My console terminal is going to be a VT131. In general, I'm not much interested in tethering my old machines to new ones for life support if I don't have to.
 
Oh by the way: I haven't forgotten about building your latest tu58em release on my Mac, but I've gotten temporarily sidetracked by other things. The new version is causing some extra problems because it uses some time-related stuff that's not present in the libraries on the Mac.
 
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