test-drb April 1999

test-drb@ccmp.vtda.org

170 participants
1190 discussions

How scarce (valuable) is core for the PDP-8?

by allisonp＠world.std.com

<OK, how about it. Put a ring of compasses around the wire with needles str <enough magnetised that they will stay pointing N-S around the ring regardle <the Earth's field. < <Can you then flip them with a current? A very good visual demonstration of <core works! Yep, That would be good to watch but that's really a demo of the fields around conductors (imporant building block). Allison

25 years, 2 months

HP 1000 on eBay : auctioned by unresponsive bidder

by ss＠allegro.com

Hi, I was about to send this just to ccauction list, but I realized that some ClassicCmp readers might not read ccauction ... and they might have an interest. In a rather misleading title: "antique Altair-like HP-1000 M-series computer" dschambe(a)uiuc.edu is selling a partially gutted HP 1000 computer. http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=95719221 This seller has consistently refused to respond to my email about two items that I got for low bids on prior auctions...so I have never been able to finalize the purchase. If anyone from this list does bid on the HP 1000, and wins, please encourage this guy to honor his *existing* committments before sending him money! thanks! sieler(a)allegro.com

25 years, 2 months

Cores, light bulb goes on ...

by cmcmanis＠freegate.com

Core memory, the saga continues. Ok after spending much of the weekend trying to get my core driver working, and feeling really good about having all the parts I needed in my spares box, I realized I had built half of an h-bridge. Since I had already designed a really nice MOSFET based h-bridge that could switch 10 - 15 amps for my robots I slapped my head and went "Doh!" Anyway, so I wired up my #2 nut with sense wire to the h-bridge and start slapping current back and forth through my nuts. :-) Seriously though when viewed on 'scope it looks something like: +--+ | | Ch1 -+ +----+ +----- | | +--+ +--+ Ch2 -+ +----+ +----- +--+ UNTIL you get to about 7.5 amps or so, and then it looks like: +--+ | | Ch1 -+ +----+ +----- | | +--+ +--+ Ch2 ---+ +----+ +----- +--+ So I stared at it a bit and the little bulb went on between my ears. The first pulse "writes" a zero to the core, if the core is either already magnetized with a zero, or has nothing in it, then the sense line sees the deta-B (change in magnetic field) and a current is induced in the wire. When the second pulse comes along it "writes" a one into the core, same effect on the sense wire. The clever part comes when your "write" a zero to a core that has a one already written to it. In this case the current in the wire induces its standard magnetic field, but that field is _cancelled_ by the field already in the core, thus for a period of time the sense line sees no change in magnetic flux, and so no current is induced. Then however the core switches to 0 and the sense wire sees that change in flux and out comes the induced pulse now delayed from the initial point by a time controlled by how long it took to saturate the core and switch it. The gap between the pulse start and the sense pulse is used to tell whether or not the core had a 1 in it. Now in the DEC design what happens after the read pulse (which is really a "write zeros" pulse, is they take the data they just read and re write with the write ones pulse. However this time since the sense lines aren't needed to figure out what the cores had in them, they use them for "inhibit" currents. Remembering that the cores were all written to zero by the 'read' when the write 'ones' pulse comes along you don't want it writing cores that you want to keep zero (they had zero before). So a current that is in opposite direction of the write current is sent down the sense lines where zeros should be kept. The magnetic field generated by these "inhibit" currents cancel the magnetic field created by the "write ones" current and thus prevents those cores with a 'zero' in them from being written to '1'. -------------------------- Cool stuff, now it raises some new questions: 1) Do you want your pulses to be long enough to switch the core exactly, or longer? (eg does writing a zero just cancel a one or does it cancel the one and write a zero in its place?) 2) Why not just gate the write one current pulse? That would save on the inhibit current stuff. 3) What properties of a material make it easier to switch at lower currents? I don't want to build a core plane with nuts if I need 8 amps to switch them. --Chuck McManis

25 years, 2 months

FW: VAX 6500 in Minneapolis.

by kstumpf＠unusual.on.ca

PLEASE REPLY DIRECTLY TO THE AUTHOR OF THE ORIGINAL MESSAGE. >Reply-To: <kenp(a)trlab.com> >From: "Ken Peck" <kenp(a)trlab.com> >To: <kstumpf(a)unusual.on.ca> >Subject: Computer Hardware for Museum >Date: Mon, 26 Apr 1999 16:28:02 -0400 >X-MSMail-Priority: Normal >Importance: Normal >X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 >X-UIDL: e7780be67b36c9d8688e16fdc0bca942 > >Kevin, > >There is a Vax 6500 in Minneapolis, >Minnesota that will be de-installed in June. I thought perhaps there might >be some interest in the historical value of it for some collector or museum. >If you or someone you know might be interested, please let contact me. > >Regards, > >Ken Peck >Total Renal Laboratories, Inc. >1991 Industrial Dr. >Deland, Fl. 32724 >800.604.5227 > > > ---------------------------------------------------------------------------- ------------------------------- Kevin Stumpf * Unusual systems * www.unusual.on.ca +1.519.744.2900 * EST/EDT GMT - 5 Collector - Commercial Mainframes & Minicomputers from the 50s, 60s, & 70s and control panels and consoles. Author & Publisher - A Guide to Collecting Computers & Computer Collectibles * ISBN 0-9684244-0-6 .

25 years, 2 months

The "FIRST PC" and personal timelines (Was: And what were the80s

by edick＠idcomm.com

The previous comment should have made it obvious it was NOT within the reach of the "average" American. First of all, it was over a month's pay for the average American, it was equivalent to six months' groceries for a family of four, and you could get a refrigerator or a washer, neither of which were routine discretionary expenditures for the "average" American of that time. That was during and immediately after the Korean war, when a 4-bedroom house on a 1/4-acre lot cost $4600. That same house, now, in California would cost you $4600 a month to rent. People's attitudes about what's important enough to spend your money on have changed considerably. $300 was not an expenditure an "average" American would consider lightly in 1952. That was the year I came to this country. There was an election between Adlai E. Stevenson (Democrat) and Dwight D. Eisenhower (Republican). It was BEFORE the first test of a hydrogen bomb. People weren't crazy then as they are now . . . and all the loose nuts hadn't yet learned to run to California. Dick -----Original Message----- From: Sellam Ismail <dastar(a)ncal.verio.com> To: Discussion re-collecting of classic computers <classiccmp(a)u.washington.edu> Date: Thursday, April 22, 1999 10:16 PM Subject: Re: The "FIRST PC" and personal timelines (Was: And what were the80s >On Thu, 22 Apr 1999, Richard Erlacher wrote: > >> No, what's relevant isn't the technology and its state of maturity, but the >> comparison of the relative value of the numbers. Today, it's just assumed >> that if you buy an item for $300 and it subsequently breaks, you shrug your >> shoulders and throw it away. Back in the '50's, not many people were silly >> enough to do that. > >So what? $300, even back in the 50s, was still realistically within the >price range of the average American. A multi-million dollar mainframe was >not. $300 vs $$$millions is a significant difference. > >Sellam Alternate e-mail: dastar(a)siconic.com >--------------------------------------------------------------------------- --- >Don't rub the lamp if you don't want the genie to come out. > > Coming this October 2-3: Vintage Computer Festival 3.0! > See http://www.vintage.org/vcf for details! > [Last web site update: 04/03/99] >

25 years, 2 months

Good Weekend, bad weekend...

by Philip.Belben＠pgen.com

Jim Willing: > I've added a fairly complete Tektronix 4054 graphics computer system to the > collection. Along with it came a hard copy unit, external tape drive, a > rather large flat bed plotter, and a full set of docs and tapes! You. Lucky. Beggar. (Green with envy) Philip. (sorry there's not much content in this message, but I had to get it off my chest. More and more 4050 series coming out of the woodwork! Keep up the good work!)

25 years, 2 months

How scarce (valuable) is core for the PDP-8?

by Philip.Belben＠pgen.com

><My first thought was something like a small compass near each bit. I want ><to avoid lights since I think they are less engaging, less an indicator ><that something has happened. Ideally this should be an attractive looking ><toy, that sparks curiousity. > > The ferrite would not show enough external field change to be a reliable > indicator. However when the wires were driven they indeed would! OK, how about it. Put a ring of compasses around the wire with needles strongly enough magnetised that they will stay pointing N-S around the ring regardless of the Earth's field. Can you then flip them with a current? A very good visual demonstration of how core works! Philip. BTW Siemens make some torroidal cores down to 1mm thick ferrite, slightly larger in other materials. RS Components stock some - http://rswww.com/ and go in through the catalogue: "Electronics", "Transformers/Inductors/Ferrites", "Ferrites", "Torroids" (sic). There are even data sheets but I didn't manage to download them.

25 years, 2 months

PC question

by allisonp＠world.std.com

<Yesterday, at the KS10 move, I came away with two IBM PCs, but I <don't know enough about them to know if they are the AT or XT <models... they both have a 5.25" floppy and a hard drive, and <both have color monitors. One was a 5150 (xt) the other was a 5170 (also XT) If all fails look at the cpu: XT 8088 or 8086 AT 80286 or later Allison

25 years, 2 months

Powerlines

by Philip.Belben＠pgen.com

I'm not sure whether this was satisfactorily cleared up. Anyway, the message was still on my list of Classiccmp mails to be answered when I finally caught up with reading them this pm. >> > Realy 234V (strange) and 180 degree ? Where do you know ? By definition ? >> > Just remember, if you tap between 2 phases of a 3~ signal you still get >> > a perfect sinus and you can't decide if it is a single phase or part of >> > a 3 phase signal. Ok, I'm always learning new things on this earth :9 >> > The numbers just saemed to fit well. >> I'm sure the power company has a legal obligation to keep the voltage >> within a certain range of values. Although, I don't know exactly what that >> range is. I think 117 is probably the optimal value for each of the legs >> giving 234 for the total. I've heard it referred to as 110, 115, 117, and >> 120. Since the actual voltage varies any of these could be correct. > > Anybody out there knowing the US regulations ? AFAIR somewhen in the > late 70s the acording definitions have been worldewide standardized > on 115V/200V and 230/400V - the intention was to allow manufacturers > (especialy the ones for power transmission systems) to develop more > efiecently and to lower building costs, since within the lower power > range (up to some MW) designs could be standardized on a simple level. >> Since it is a simple transformer, the phases are 180 degrees out of phase >> (by definition). That's assuming a balanced resistive load. Of course, that >> could change under a heavy inductive or capacitive load but, that's an >> extreme and won't normally present a problem. > > Still not an argument against 2 phases from an 3~ signal. 1. Voltage The voltage will be declared by the supply company to be some value +/- some tolerance. This will usually be according to a national standard. The transformer will usually have a higher voltage on its rating plate - if the nominal voltage is 115 or 117 volts, the transformer may be rated at 120V. People near the transformer will get 120V, people at the far end of the cable will get 110V. My house is very near the transformer so I get 248V on a nominal 230V supply (NB when it was nominally 240V I got 248V. Nobody has adjusted the transformer...) 2. Phase. As I understand it the usual practice in the US is take _either_ a phase and earth (neutral) _or_ two phases of the HV supply and feed a single phase transformer from this. The LV side of the transformer is (say) 240V with a centre tap. The centre tap is earthed and provides the neutral connection, the outer two taps are then both hot at 120V, 180 degrees apart. This is true _even if_ the primary (HV winding) is connected between two phases of the HV 3-phase system. In the UK the usual practice is to connect all 3 phases of the HV (almost invariably 11kV phase to phase) to a delta-star 3-phase transformer. The secondary, the star-connected winding provides 3 phases and neutral. Neutral is earthed at the transformer. Protective earth can be provided by _either_ a separate wire from the main earth at the transformer _or_ an earthing electrode at each customer's site _or_ the neutral is earthed at a large number of points on the system and the customer's protective earth is bonded to neutral at the point of entry of the supply. In all cases the customer sees 240V line to neutral; if he gets more than one line (hot) connection, they will be 120 degrees apart. In remote locations, only 2 phases of the 11kV system are taken to the site. Small loads get a single phase 11kV/250V transformer with one end of the LV earthed; larger loads get a single phase 11kV/500V transformer with a centre tap earthed. Some farm equipment (I am told - I have never seen this) is rated for 480V single phase. It is very unusual for a domestic installation to get more than one phase and neutral. But 3-phase can be done - the supply company don't mind putting it in if they think you'll buy a lot of electricity! Philip.

25 years, 2 months

GEM GPL'd?

by healyzh＠aracnet.com

Here is a site that claims Caldera just GPL'd GEM. http://www.devili.iki.fi/cpm/gemworld.html I've no idea of the validity of this statement, but apparently the guy running the site browbeat Caldera into releasing it. They've got a pretty good selection of GEM PC software, and it sounds like other stuff elsewhere on the site. If you're interested in such things. Zane | Zane H. Healy | UNIX Systems Adminstrator | | healyzh(a)aracnet.com (primary) | Linux Enthusiast | | healyzh(a)holonet.net (alternate) | Classic Computer Collector | +----------------------------------+----------------------------+ | Empire of the Petal Throne and Traveller Role Playing, | | and Zane's Computer Museum. | | http://www.dragonfire.net/~healyzh/ |

25 years, 2 months

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test-drb April 1999