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1 Jan, 54 tweets, 15 min read
Tube Time: a 2021 retrospective 🧵
(and stuff you might have missed!)
i started off with this nice video clip of an old-school flashing lamp (like the red-tipped ones used to flash christmas lights)
then tried to resurrect a very corroded pinball circuit board.
for Black History Month, i profiled Mark Dean.
Mark Dean helped design the CGA graphics card. i also dug into the design myself, and gave it a programmable palette with just a single extra chip!
some threads take lots of work, like the CGA thread. other threads are just throwaways (and often get more R/Ts, lol.)
i fired up an ancient video card, one designed for an LSI-11 system.
since it's harder to find NE558 chips, i designed an open source drop-in replacement!
here's a crappy LED light bulb that i reverse engineered. it's unsafe! read the thread to find out why.
branching out from my typical technical fare, i investigate Silicon Valley's very own ghost town!
i got an IBM PS/2 model 30, and fixed it up.
what does the "808" in the name of the famous TR-808 drum machine stand for? i had a theory (which turned out to be wrong) but the journey was amazing!
i randomly decided to adapt a PC trackball to work with my Amiga computer.
the first portable video recorder came out in...1967! i found one of these, and fixed it up.
a fellow vintage computer collector loaned me his PS/2 model 80, so i fixed it up.
i picked apart a strange and terrible hack in the original PS/2 model 80 design.
played some games with an ancient and loud 160 megabyte hard drive, and wound up trying to decode the raw RLL data.
oh, and i released the design for my Graphics Gremlin open source ISA video card! sadly only a few people were able to build them since the FPGA has been out of stock the entire year. i have a feeling it'll be out of stock for all of 2022 as well. 😬
i fixed up a paper tape punch. now i can make my own confetti!
@Foone and I are always trolling each other. it's great 😉
luck found me again since i was able to get a rare IBM 3270 PC! this bizarre beast lets you multitask DOS and a 3270 terminal session using overlapping windows!
🐊🐊
speaking of luck, i went to the Vintage Computer Festival West this year, and found *exactly* the book i needed!
at VCF i found a neat mouse that converts into a trackball.
i met Bill Mensch, one of the designers of the 6502!
this year, the IBM PC turned 40!
in celebration of the PC's 40-year anniversary, i managed to duplicate the official launch photo.
some of you who watch Curious Marc's channel on YouTube might have noticed a familiar face.
(i started helping out Marc and friends with some of the projects featured on his channel)
The Secret Life of Traffic Cones
that would actually be a pretty cool book, but you'll have to make do with this thread instead.
started out investigating a really weird sound card, and ended up investigating a really weird mouse. 🤷‍♂️
based on some of the work i was doing with Marc, i was inspired to fix up an old Tally punch tape reader.
you can watch the CuriousMarc video for the whole story, but i designed a little 3d-printed PLCC plug adapter to help with the troubleshooting.
where do all these old computers come from? i just really enjoy fixing them.
i started working on a Williams tube memory after finding *an actual 1950s Williams tube* in my collection! (the work is still ongoing--it turns out amplifiers can be hard to design!)
bought a DataRover device that runs a really old mobile operating system called Magic Cap.
if you like epic repair threads, here's another good one.
in another stroke of luck, i wound up with an IBM AT, and inside was a rare IBM Professional Graphics Controller! it made me feel better about losing an eBay auction where the card sold for over $500!
at the beginning of the year i made a thread about Silicon Valley's ghost town, but i hopped on my bike and went to go visit! (well, at least get close, it's in a protected wildlife area)
i have too many computers. do i have too many computers?
a friend of mine asked me to repair a SAS RAID card, so i did a little microsoldering.
California Extreme is a yearly video game convention in Silicon Valley. this year it was tiny due to Covid restrictions, but i was able to visit and saw a really neat electromechanical driving game!
🪲
this was one of the more challenging projects. a friend of mine asked me to fix this strange 8086 accelerator card, and it turned out to be a wild ride! read the thread to find out about my copper brush reverse engineering trick.
oh, and i got a 286 accelerator card for my own computer and managed to get it working as well.
check out this majestically overbuilt System 370 channel simulator.
sadly, i got nerd sniped by clickbait. happens to the best of us
this was actually super cool. ancient computers had truly gigantic cables and connectors!
someone in a Discord chat mentioned that punch-card-controlled washing machines exist; naturally, my curiosity was piqued.
wow, i got a Hercules graphics card! but it was missing the character ROM chip, so i had to improvise...
right before christmas i received my Tilt Five AR glasses. playing games is cool, but i've got some other ideas...
and here i am at the end of 2021, playing with old hard drives again.
and that's it! that was my 2021.
thank you all for your suggestions and replies. i am plenty inspired by you folks, and i hope that you find Tube Time to be a little island of sanity in the often treacherous waters of this website.

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31 Dec 21
there's something unique about this potentiometer. Image
it has three large ball bearings in the back, but what for? (read on!) Image
the three ball bearings form a planetary "gear" reduction, turning this into a 10-turn potentiometer!
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31 Dec 21
maybe i should do a Therac-25 deep dive, but there are entire books written about it...
i remember reading about it in a book, Fatal Defect - Chasing Killer Computer Bugs. but there are inaccuracies and simplifications.
there's also this Reddit thread: reddit.com/r/programming/…
(the VT link is dead but archive.org has it)
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27 Dec 21
fantastic aesthetic of the most accurate pendulum clocks ever built.
this 1920s clock technology could be accurate to within 1 second per year, and measurements in the 1980s confirmed that at least one such clock was accurate to within a tenth of a second per year.
here's the 1984 paper measuring the accuracy of such a clock. leapsecond.com/pend/pdf/1986-…
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22 Dec 21
these little guys are 0805 surface mount devices, but you'll never guess what they are! hint: they're not resistors!
not fuses, not capacitors, not diodes, not LEDs, not antennas...
it's in stock at Mouser. no guesses?
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21 Dec 21
today's project is to fix this old Seagate ST-412 hard drive. 10MB, full height, and really loud! Image
here's a problem: the positioner stepper seems to move around randomly on power up. it's supposed to wait until the rpm goes nominal before moving. could be an issue with one of the motor phases.
looks like the stepper is controlled from an MCU. but there's some electronics in between i should check. Image
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4 Dec 21
check this out! it's an accelerator card that turns your 8088 PC or XT into a 286. let's try and get it running... 🧵 Image
hmm, there's some damage to the sockets Image
the card is an Orchid Tiny Turbo 286. Image
Read 52 tweets

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