- cctalk - classiccmp.org

by Rob Jarratt

(sending again from a different email address as I don't think my first email got through, apologies if this is a duplicate) I have a VT100 that I was working on a while back and then set aside for a bit. I have started to look at it again. I have noticed that the Video Shift Register, a 74S299, gets very hot, I can smell the heat and the chip gets almost too hot to touch, reaching almost 40 celsius. I have a working VT102 for comparison and the same chip there does not get so hot (it reaches about 30 celsius). I have already tried replacing the chip, but the new one gets equally hot. I looked at the signals the chip is receiving and the one that stands out as different is the CLK input (pin 12). It looks like this: https://rjarratt.wordpress.com/wp-content/uploads/2024/04/vt100-74s299-clk-s ignal.png. On the VT102 it looks like this: https://rjarratt.wordpress.com/wp-content/uploads/2025/11/vt102-74s299-clk-s ignal.png. It is much spikier on the VT100 and I was told at one point that this could be the cause of the hot running for the chip. Is that a reasonable assumption? Assuming the spikes are the cause of the hot running. I am trying to see why there is a difference. I have noticed that on the VT102 there is a 68R resistor between the DC011 which produces the signal and the 74S299. You can see this as R86 in the VT101 printset https://bitsavers.org/pdf/dec/terminal/vt101/MP-01066-00C_VT101_Family_Field _Maintenance_Print_Set_Apr82.pdf (p47 of the PDF). The VT100 printset dated Feb 82 https://bitsavers.org/pdf/dec/terminal/vt100/MP00633_VT100_Schematic_Feb82.p df shows an inductor L8 being used (PDF p17), but my VT100 does not have this and so must be described by the March 80 printset https://bitsavers.org/pdf/dec/terminal/vt100/MP00633_VT100_Mar80.pdf (PDF p17). Could the absence of L8 explain the spikier DOT CLK signal and the hotter 74S299? Incidentally, I suspect that the flyback transformer on my VT100 has failed. If anyone has a flyback transformer going spare, especially in the UK, then I would love to hear from you. Thanks Rob

35 minutes

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Ownership of microcomputing

by Murray McCullough

One of the greatest joys of classic computing was running what you wanted on your own computer. What has happened in the intervening years? Have ‘software walls’ created a computing environment that benefits software gate-keepers(owners of computing technology) by monopolizing creativity, freedom to program and establishing a defacto ‘true ownership’. Will the future be this or will it be more like the earliest years of microcomputing? Murray 🙂

3 hours, 1 minute

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BDV11 programming information

by Peter Ekstrom

Does anyone know if there is any programming information about the BDV11 card? I have disassembled the ROM files for it and I see they do various operations with the registers on the card, but it is not clear to me exactly what they are doing. - Peter

14 hours, 6 minutes

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WINdows-1985

by Murray McCullough

According to history Windows 1 was introduced to the world on Nov. 20, 1985, 40 years ago, minus 2 days. Prior to this Windows was first announced in 1983(vaporware) but…An even earlier development was Interface Manager. What we have now is much more and ‘better’ but for classic computing I still prefer WIN 3.1. Happy computing. Murray 🙂

2 days, 7 hours

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Depraz Mouse, Type D 83 / P, Excellent Condition, Looking to Establish Value and Sell

by microprint314＠gmail.com

I found a Depraz mouse the other day (Type D 83 / P) while going through moving boxes. I used to - long time ago - make things out of broken or disassembled computer gear. There was the most amazing store in Dover, NJ called Second Byte where I spent too much time and money (according to my ex-wife). I purchased this mouse 30 years ago with no particular project in mind, and it has just stayed packed away. I'm looking to sell it but I admittedly don't know what it's worth. I see two of them on eBay for $20-$30K, but don't see any Sold Items as a reference. Those sale prices sound largely aspirational. The mouse is in pretty amazing physical condition, with only basic scuffing on the red surface. The larger spots you see are reflections. The cable has scuffs but no fraying at all. The ball turns when the mouse is rolled. No pins are bent on the connector (RS-232 / DB9?). The three buttons click. Any insight - or offers - is welcomed. Thanks.

3 days, 2 hours

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Re: Seagate half high hard drive face plate & cables

by Peter Ekstrom

Mike, Where are you located? I am in the US in Georgia. I have several of each of those connectors. - Peter On Fri, Nov 21, 2025 at 3:42 PM Mike Katz <bitwiz(a)12bitsbest.com> wrote: > 20 and 34 pin edge (2 each) and 20 and 34 pin female dual in line (1 > each). I have the ribbon cable and the tool > > Thank you > > On Nov 21, 2025 12:19 PM, Peter Ekstrom <epekstrom(a)gmail.com> wrote: > > Mike, > > Which connectors is it you need? > > -Peter > > On Fri, Nov 21, 2025 at 1:08 PM Mike Katz via cctalk < > cctalk(a)classiccmp.org> wrote: > > > Paul, > > The connectors are about $5 apiece and I would need 7 connectors. I > have the cable and tool. > > My goal for asking was to see if anyone had a spare cable or two and > save them from eventually going in the land fill. > > Thank you for your help, > > Mike > > On 11/21/2025 11:17 AM, Paul Koning via cctalk wrote: > > For that matter, since the connectors are insulation displacement type, > you can assemble your own: buy the connectors and a length of table, cut > pieces to size, and assemble the connectors onto the cable. A press is > normally used for that, but a vise should do the job too. > > > > paul > > > >> On Nov 21, 2025, at 11:03 AM, Paul Koning via cctalk < > cctalk(a)classiccmp.org> wrote: > >> > >> General comment on cables like that: in the past I have obtained flat > ribbon cable assemblies from Digikey. If you're dealing with a cable > that's simply a ribbon of width N and a connector at each end, companies > like that can supply them easily and cheaply, in any length you want. > >> > >> paul > >> > >>> On Nov 20, 2025, at 9:40 PM, Mike Katz via cctalk < > cctalk(a)classiccmp.org> wrote: > >>> > >>> Does anyone out there have a spare 1/2 high 5 1/4" Seagate MFM hard > drive face plate (ST-221, ST-251, etc.) that they can let go cheap? > >>> > >>> And also a 34 conductor dual drive cable and a single 20 on single > drive cable? > >>> > >>> Thank you. > >>> > >>> Contact me off list at bitwiz(a)12bitsbest.com > > >

3 days, 4 hours

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Seagate half high hard drive face plate & cables

by Mike Katz

Does anyone out there have a spare 1/2 high 5 1/4" Seagate MFM hard drive face plate (ST-221, ST-251, etc.) that they can let go cheap? And also a 34 conductor dual drive cable and a single 20 on single drive cable? Thank you. Contact me off list at bitwiz(a)12bitsbest.com

3 days, 7 hours

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Various vintage computers and peripherals for sale

by martin .

As we're emigrating soon, I am starting so find a new home for my collection of vintage computers and peripherals. On offer today is: Dec PDP 8E* ==========on a standA list of modules included in the link below. including with the machine comes: - Rail mounting hardware - Spare power supply - A long flat cable - Bootstrap card M847E - 32k SRAM + Bootstrap card from Vincent Slyngstad (new kit, unassembled) ASR33 Teletype* ==============on its original stand Hazeltine H2000 terminal* ========================in pristine condition on a stand Hazeltine H2000 terminal========================probably not working (got somehow damaged during transport from last seller to me, and I never got around checking out what's wrong) Tektronix 4014-1* Graphics Terminal ===================================on its original stand Please make an offer for either some or for all of the items (to martin(a)meiner.ch). *) Items marked with a star were functioning well a few years ago when I was actively acquiring them. As times went by, it could be that one or the other may need TLC. I have not tested them again for full functionality. Items are located near Zurich/Switzerland. It is the buyer's responsibility to either pick the items up or to arrange packing and shipping by a forwarder. Here a link to cloud storage showing photos and other information of the units: http://e.pc.cd/o3sy6alK More equipment to follow in a few weeks / months (will rather be elder calculators).

3 days, 12 hours

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Replacements for DEC 3639

by Christian Corti

It seems that nowadays you can't get *any* replacement for failing DEC 3639 aka 2N3639 transistors. All parts are obsolete and unobtanium, e.g. 2N3640, PN3640, MMBT3640 and so on. So, what can be used instead? The most important electrical parameter is the storage time. It needs to be *very* low, around 20-30 ns. Does it mean that a failing PDP-8 will stay a dead PDP-8 from now on? Christian

3 days, 16 hours

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ST-251 MFM Hard Drive sector size question

by Mike Katz

I have an ST-251 42MB MFM hard disk drive. The documentation says the drive is 512 bytes per sector. I don't know if this is fixed (hard sectored) or not. My problem is my operating system (OS/9 Level II) wants 256 bytes per sector. The OMTI 20C-1 controller can handle that but I'm not sure if the ST-251 can. Does anyone know if the ST-251 can support 256 bytes per sector and/or how to configure it for 256 bytes per sector? Thank you, Mike

6 days, 3 hours

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