Testing A Soviet 1000 Volt Insulation Tester From 1985

March 17, 2026 by Maya Posch 8 Comments

Although the term ‘Iron Curtain’ from the Cold War brings to mind something like the Berlin Wall and its forbidding No Man’s Land, there was still active trade between the Soviet Union and the West. This included devices like the M4100/4 insulation tester that the [Three-phase] YouTube channel recently looked at, after previously poking at a 1967 USSR resistance bridge.

This particular unit dates to 1985, and comes in a rather nice-looking case that somewhat looks like bakelite. It’s rated for up to 1 gigaohm, putting out 1,000 V by using the crank handle. Because of the pristine condition of the entire unit, including seals, it was decided to not look at the internals but only test its functionality.

After running through the basic usage of the insulation tester it’s hooked up to a range of testing devices, which shows that it seems to be mostly still in working condition. The first issue noticed was that the crank handle-based generator was a bit tired, so that it never quite hit the maximum voltage.

With no parallax correction and no known last calibration date, it still measured to about 10% of the actual value in some tests initially, but in later tests it was significantly off from the expected value. At this point the device was suspected of being faulty, but it defied being easily opened, so any repair will have to be put off for now. That said, it being in such good condition raises the prospect of it being an easy repair, hopefully in an upcoming video.

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It’s 1979 – What Exactly Did That ∫ Key Do?

March 10, 2026 by Donald Papp 15 Comments

[Michel Jean] asked a question few others might: what exactly is going on under the hood of a classic HP scientific calculator when one presses the ∫ key? A numerical integration, sure, but how exactly? There are a number of useful algorithms that could be firing up when the integral button is pressed, and like any curious hacker [Michel] decided to personally verify what was happening.

[Michel] implemented different integration algorithms in C++ and experimentally compared them against HP calculator results. By setting up rigorous tests, [Michel] was able to conclude that the calculators definitely use Romberg-Kahan, developed by HP Mathematician William Kahan.

Selected by HP in 1979 for use in their scientific calculators, the Romberg-Kahan algorithm was kept in service for nearly a decade. Was it because the algorithm was fast and efficient? Not really. The reason it was chosen over others was on account of its robustness. Some methods are ridiculously fast and tremendously elegant at certain types of problem, but fall apart when applied to others. The Romberg-Kahan algorithm is the only one that never throws up its hands in failure; ideal for a general-purpose scientific calculator that knows only what its operator keys in, and not a lick more.

It’s a pretty neat fact about classic HP calculators, and an interesting bit of historical context for these machines. Should you wish for something a bit more tactile and don’t mind some DIY, it’s entirely possible to re-create old HP calculators as handhelds driven by modern microcontrollers, complete with 3D-printed cases.

Thanks to [Stephen Walters] for the tip!

How The Chornobyl NPP Got Modernized In The 1990s

March 7, 2026 by Maya Posch 5 Comments

During the 1990s the Chornobyl Nuclear Power Plant – formerly the Chernobyl NPP – continued operating with its remaining three RBMK reactors, but of course the 1970s-era automation with its very limited SKALA computer required some serious modernization. What was interesting here is that instead of just replacing this entire Soviet-era mainframe with a brand-new 1990s one, the engineers responsible opted to build a new system – called DIIS – around it. This is detailed in a recent video by the [Chornobyl Family] on YouTube.

This SKALA industrial control system was previously detailed in a video, covering this 24-bit mainframe computer and its many limitations. It wasn’t quite a real-time control system, but it basically did what it was designed to do. Since at the time it was not clear for how long these three RBMKs would be kept running, they didn’t want to go overboard with investments either.

Ultimately Unit 2 only was active until 1991 due to a turbine fire, Unit 1 until 1996 and Unit 3 was shutdown for the last time in 2000, so this a sensible decision. During those years, an auxiliary information-measurement system (DIIS) was the big upgrade, which got bridged into SKALA via a Ukrainian-made SM-1210 minicomputer, with the latter connected to an 80386 PC which itself was connected to an ARCnet hub.

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How To Restore Your 19th-Century Lancashire Boiler To Hold 120 PSI

February 23, 2026 by Maya Posch 14 Comments

The Industrial Revolution was powered by steam, with boilers being a crucial part of each steam engine, yet also one of the most dangerous elements due to the high pressures involved. The five Lancashire boilers at the Claymills Pumping Station are relatively benign in this regard, as they operate at a mere 80 PSI unlike e.g. high-pressure steam locomotives that can push 200 – 300 PSI. This doesn’t mean that refurbishing one of these boilers is an easy task and doesn’t involve plugging a lot of leaks, as the volunteers at this pumping station found out.

At this Victorian-era pumping station there are a total of five of these twin-flue Lancashire boilers, all about 90 years old after a 1930s-era replacement, with them all gradually being brought back into service. The subject of the video is boiler 1, which was last used in 1971 before the pumping station was decommissioned. Boilers 2 and 3 were known to be in a pretty bad condition, and they needed a replacement for boiler 5 as it was about to go down for maintenance soon.

Although the basic idea behind a Lancashire boiler is still to boil water to create steam, it’s engineered to do this as efficiently as possible to save fuel. This is why it has two flues where the burning coal deposits its thermal energy, which then goes on to heat the surrounding water. The resulting pressure from the steam also means that there are a lot of safeties to ensure that things do not get too spicy.

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Retrotechtacular: Bleeding-Edge Memory Devices Of 1959

February 21, 2026 by Maya Posch 6 Comments

Although digital computers are – much like their human computer counterparts – about performing calculations, another crucial element is that of memory. After all, you need to fetch values from somewhere and store them afterwards. Sometimes values need to be stored for long periods of time, making memory one of the most important elements, yet also one of the most difficult ones. Back in the 1950s the storage options were especially limited, with a 1959 Bell Labs film reel that [Connections Museum] digitized running through the bleeding edge of 1950s storage technology.

After running through the basics of binary representation and the difference between sequential and random access methods, we’re first taking a look at punch cards, which can be read at a blistering 200 cards/minute, before moving onto punched tape, which comes in a variety of shapes to fit different applications.

Electromechanical storage in the form of relays are popular in e.g. telephone exchanges, as they’re very fast. These use two-out-of-five code to represent the phone numbers and corresponding five relay packs, allowing the crossbar switch to be properly configured.

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PROFS: The Office Suite Of The 1980s

February 11, 2026 by Al Williams 14 Comments

Today, we take office software suites for granted. But in the 1970s, you were lucky to have a typewriter and access to a photocopier. But in the early 1980s, IBM rolled out PROFS — the Professional Office System — to try to revolutionize the office. It was an offshoot of an earlier internal system. The system would hardly qualify as an office suite today, but for the time it was very advanced.

The key component was an editor you could use to input notes and e-mail messages. PROFS also kept your calendar and could provide databases like phonebooks. There were several key features of PROFS that would make it hard to recognize as productivity software today. For one thing, IBM terminals were screen-oriented. The central computer would load a form into your terminal, which you could fill out. Then you’d press send to transmit it back to the mainframe. That makes text editing, for example, a very different proposition since you work on a screen of data at any one time. In addition, while you could coordinate calendars and send e-mail, you could only do that with certain people.

In general, PROFS connected everyone using your mainframe or, perhaps, a group of mainframes. In some cases, there might be gateways to other systems, but it wasn’t universal. However, it did have most of the major functions you’d expect from an e-mail system that was text-only, as you can see in the screenshot from a 1986 manual. PF keys, by the way, are what we would now call function keys.

The calendar was good, too. You could grant different users different access to your calendar. It was possible to just let people see when you were busy or mark events as confidential or personal.

You could actually operate PROFS using a command-line interface, and the PF keys were simply shorthand. That was a good thing, too. If you wanted to erase a file named Hackaday, for example, you had to type: ERASE Hackaday AUT$PROF.

Styles

PROFS messages were short and were essentially ephemeral chat messages. Of course, because of the block-mode terminals, you could only get messages after you sent something to the mainframe, or you were idle in a menu. A note was different. Notes were what we could call e-mail. They went into your inbox, and you could file them in “logs”, which were similar to folders.

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Restoring The Soul Of A 1940s Radio

February 4, 2026 by Bryan Cockfield 13 Comments

Although we do often see projects that take antiques and replace some or all of their components with modern equipment, we can also sympathize with the view that (when possible and practical) certain antique electronics should be restored rather than gutted. [David] has this inclination for his 1948 GE radio, but there are a few issues with it that prevented a complete, period-correct restoration.

The main (pun intended) issue at the start of this project was safety. The original radio had a chassis that was just as likely as not to become energized, with the only protection being the plastic housing. [David] set up an isolation transformer with a modern polarized power cable to help solve this issue, and then got to work replacing ancient capacitors. With a few other minor issues squared away this is all it took to get the radio working to receive AM radio, and he also was able to make a small modification to allow the radio to accept audio via a 3.5mm jack as well.

However, [David] also has the view that a period-correct AM transmission should accompany this radio as well and set about with the second bit of this project. It’s an adaptation of a project called FieldStation42 originally meant to replicate the experience of cable TV, but [Shane], the project’s creator, helped [David] get it set up for audio as well. A notable feature of this system is that when the user tunes away from one station, it isn’t simply paused, but instead allowed to continue playing as if real time is passing in the simulated radio world.

Although there are a few modern conveniences here for safety and for period-correct immersion, we think this project really hits the nail on the head for preserving everything possible while not rolling the dice with 40s-era safety standards. There’s also a GitHub page with some more info that [David] hopes to add to in the near future. This restoration of a radio only one year newer has a similar feel, and there are also guides for a more broad category of radio restorations as well.

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