February 2025 - cctalk - classiccmp.org

by Mattis Lind

I am about to get a NCR EM-D2 card reader, but I can not find much documentation on it. Is there anyone here that has documentation on it? Preferably a maintenance manual. A couple of years ago (perhaps in February 2021 if one studies how they indexed the file in their storage) there was a sale of a maintenance manual on Ebay according to the below Worthpoint link. https://www.worthpoint.com/worthopedia/1965-ncr-em-d2-punched-card-reader-3… Did anyone here buy this manual? I am very interested in a scan of this manual or possibly to purchase the manual. /Mattis

10 months, 1 week

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Mid-Atlantic Retro Computing Hobbyists Hack-a-Thon

by Jeffrey Brace

DATE: March 8 & 9, 2025 LOCATION: InfoAge Science and History Museums, Wall, NJ Fee: None *More info here*: https://vcfed.org/2025/02/13/march-hack-a-thon/

10 months, 1 week

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Looking for information on Megan Gentry, former RT-11 developer

by Hans-Ulrich Hölscher

Does anyone know anything about the whereabouts of Megan Gentry, former RT-11 developer? She left her last trace in 2020, when she ported ZEMU to RT-11.

10 months, 1 week

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Vintage Computer Festival Montreal Survey

by Jeffrey Brace

We invite you to take part in a brief, anonymous survey about VCF Montreal. Click here https://bit.ly/vcfm2026pre-en Nous vous invitons à participer à un bref sondage anonyme sur VCF Montréal. Cliquez ici https://bit.ly/vcfm2026pre-fr Jeff Brace Vintage Computer Federation Vice President

10 months, 1 week

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Use (abuse?) of a 7924 in a +24 PS...

by William Sudbrink

I'm repairing/restoring a later model MITS 8 inch floppy drive. I can not seem to find schematics for it. It is the same as Bill Degnan has here: https://vintagecomputer.net/MITS/88-DCDD/ You can see in his photos (and mine match) that the _plus_ 24 volt DC supply on the board uses a 7924 (note the 9. negative) voltage regulator, with a small heat sink, directly on the circuit board. Along with a couple of 7805s, there is a .Motorola 2n6045 screwed to the large black heat sink. All three of the devices drop into sockets on the circuit board to allow the heat sink to be easily installed/removed. On my unit, the socket for the 2n6045 was burnt to a crisp. I have replace the socket, the 2n6045, the 7924 and the electrolytic caps. When I test the +24 volt rail with a dummy load, it measures +41 volts. I don't understand this circuit. I know MITS was notorious for its power supplies. Does anyone have the schematics for this version of the 8 inch floppy? Any suggestions? Thanks, Bill S. -- This email has been checked for viruses by Avast antivirus software. www.avast.com

10 months, 2 weeks

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Re: Looking for IBM 2723

by Tony White

A 2838 card can be used instead of a 2723. keith

10 months, 2 weeks

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Re: Looking for IBM 2723

by Tony White

You can use a 2838 card instead of the 2723.

10 months, 2 weeks

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Microsoft 50 years

by Christian Liendo

I was debating sending this, but Microsoft is part of computing history and fifty years is a milestone. https://news.microsoft.com/microsoft-50/

10 months, 2 weeks

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Re: RS232 then and now

by Robert Feldman

>Message: 26 >Date: Sat, 1 Feb 2025 18:13:17 -0500 >From: Nigel Johnson Ham <g4ajq1(a)gmail.com> >Subject: [cctalk] Re: RS232 then and now > >On 2025-02-01 18:11, Chuck Guzis via cctalk wrote: >> One mystery to me was why did the industry stick with the EIA-232 levels >> for terminals and whatnot long after differential EIA-422 was >> introduced. Higher-speed, better noise immunity, single-ended power >> supply... Seems that the popular places were Appletalk and ST506 data >> lines. But not on DTE/DCE. If you were using full-voltage (±15-±25) >> at high speeds (>500Kbps), the slew rates were ridiculous. >> >> Inertia? My old 80286 motherboard had junper-selectable 232 or 422. >> >> Still have a couple of tubes of 422 drivers/receivers. >> >> --Chuck >> >DEC had RS422 available on their DLJ11J four-port interface, but I never >saw it used in the field. > The Otrona Attache has two serial ports, DA-15 female, that are jumper selectable between RS-232C, RS-422 or RS-423. Bob

10 months, 2 weeks

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A baudy tale

by Donald Whittemore

In the early 70s my employer used stand alone data entry tape units in our remote locations. We started with NCR units but then switched to Tally. In the late afternoon the data would be transmitted to the home office in Chicago for processing. Also using NCR/Tally units. We used Racal-Milgo modems. These things were about the size of a large home stereo receiver. We started at 2400 baud. The units could do 3600 or 4800 (I don’t remember which) if a circuit board strap was moved. We had locations in many cities/towns all the way out to Montana. It was decided that we needed to have the ability to switch between 2400 and the faster speed when possible. We did not want to have the locals power off the modem, open it up, remove a card and move the strap. So I got volunteered to come up with a plan. I found a place in the modem where I could mount a switch. Luckily the modem had a sliding panel on the front so the locals would not have to open the box top. Went to our fleet garage where they had the tools I needed. I made a bunch of aluminum brackets for a tiny toggle switch. Added wires to the switch. It was also decided that we could not trust the locals to do the switch install. So part of the plan included me going to all the locations and doing the install. I did not have a car at the time so I got a fleet car. Headed south to Kentucky then turned west. Don’t remember all the states I hit but I believe the last place I hit on the way home was Rockford. I remember being on a back road in Montana and I took a picture of my speedometer. I was doing 65. This was when there was a countrywide speed limit of 55. I can’t be limited by the Man. :) Back at the home office we had 6 NCR/Tally machines and only 4 modems. I built a plug panel box that had everything wired to it and used telephone jack plugs to connect the Tally’s to an available modem. The box also had switches for the modem speed. I now forget how long the whole process took. Put my DeVry AAS degree to good use. :)

10 months, 2 weeks

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cctalk February 2025