Author: Al Williams

4349 Articles

This Vintage Computing Device Is No Baby Food

July 20, 2024 by 10 Comments

Today, if you want a computer for a particular task, you go shopping. But in the early days of computing, exotic applications needed custom computers. What’s more is that with the expense of computers, you likely got one made that fit exactly what you needed and no more. That led to many oddball one-off or nearly one-off computers during that time frame. Same for peripheral devices — you built what you had to and you left the rest on the drafting table. [Vintage Geek] got his hands on what appears to be one of them: the Gerber Scientific 6200.

While Gerber Scientific is still around, we’ve never heard of the 6200. Based on the serial number, we would guess at least 62 of them were made and this one has an interesting backstory of living in someone’s home who worked at the Pentagon. We presume the tapes were erased before it was sold!

Design-wise, it is pretty standard stuff. A 19-inch rack, a standard tape drive from Kennedy, a power supply, and some cards. The box takes 240 V, so the computer didn’t get powered up, but an examination of the inside looked like this really was a one-off with handwritten labels on masking tape.

We couldn’t tell for sure if the device was a computer itself, or just a tape drive and maybe plotter interface for another computer. If you know anything about this device, we are sure [Vintage Geek] would like to hear from you.

If this does turn out to have a CPU onboard, we’d bet it is bit sliced. If you have a 9-track tape machine, you may have to make your own tapes soon.

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How Ten Turn Pots Are Made

July 19, 2024 by 5 Comments

It is easy to think of a potentiometer as a simple device, but there are many nuances. For example, some pots are linear — a change of a few degrees at the low end will change the resistance the same amount as the same few degrees at the high end. Others are logarithmic. Changes at one end of the scale are more dramatic than at the other end of the scale. But for very precise use, you often turn to the infamous ten-turn pot. Here, one rotation of the knob is only a tenth of the entire range. [Thomas] shows us what’s inside a typical one in the video below.

When you need a precise measurement, such as in a bridge instrument, these pots are indispensable. [Thomas] had a broken one and took that opportunity to peer inside. The resistor part is a coil of wire wound around the inside of the round body. Unsurprisingly, there are ten turns of wire that make up the coil.

The business end, of course, is in the rotating part attached to the knob. A small shuttle moves up and down the shaft, making contact with the resistance wire and a contact for the wiper. The solution is completely mechanical and dead simple.

As [Thomas] notes, these are usually expensive, but you can  — of course — build your own. These are nice for doing fine adjustments with precision power supplies, too.

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Retro Calculator Panders To Trekkies… Or Trekkers

July 19, 2024 by 10 Comments

Back in 1976, when calculators were not common or cheap, a company named MEGO made the Star Trekulator: a calculator sporting a Star Trek theme. However, it was a bit odd since the calculator didn’t correspond to anything you ever saw on the TV show. It was essentially a very simple calculator with a Star Trek picture and some blinking LEDs. [Computer History Archives Project] has two examples of the rare calculator and shows them off, including the insides, in the video below. We’ve also included a vintage commercial for the device a little farther down.

Inside the 5-inch by 9.5-inch cabinet was an unremarkable printed circuit board. The main component was a TI calculator chip, but there were a surprising amount of other components, including three that [Computer History Archives Project] could not identify.

MEGO was known for making Star Trek toys, including a cassette player that (sorta) looked like a tricorder and communicator walkie-talkies. We wish they’d made the calculator look like some sort of prop from the show, although the beeping noises, we suppose, were supposed to sound like the Star Trek computers.

Honestly, we want to 3D print a case to replicate this with modern insides that can drive a display to put different Trek clips and sound effects out. Now, that would be something. Maybe [Michael Gardi] can take a look at it when he’s got a spare minute. If anything, the calculator looks too advanced to be on the original series. They should have gone VFD. Although Mr. Spock has been seen with a flight slide rule (an E6-B, if we recall). We prefer our props to look like the real ones, thank you.

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A Nostalgic Look At A Kid’s Shortwave Receiver

July 18, 2024 by 10 Comments

[Mikrowave1] had a Unelco shortwave receiver as a kid. This was a typical simple radio for the 1960s using germanium and silicon transistors. It also had plug-in coils you had to insert into sockets depending on the frequency band you wanted to receive.

While simple AM radios were all the rage, they didn’t have to operate at higher frequencies. [Mikrowave1] shows some of the design tricks used to allow the radio to operate in the upper part of the spectrum. Otherwise, the radio is the usual superhet design using lower frequency germanium PNP transistors in the IF stage. You get a look inside the radio and a peek at a similar schematic along with notes on where the radio is different.

But how does it work? For an old single-conversion receiver, it works well enough. Of course, when the radio was new, there were many more interesting stations on shortwave. Today, he had to settle for some ham radio stations and CHU, the Canadian time and frequency station.

There were six pairs of coils built on top of tube sockets. The coil was actually more than a coil. There were other components in the case that adjusted other radio parameters based on the frequency.

[Mikrowave1] has been on a toy kick lately, and we’ve enjoyed it. This radio looks simple compared to the Radio Shack one that every kid wanted in the 1970s. Well. Every hacker kid, at least.

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Secrets Of The Old Digital Design Titans

July 18, 2024 by 46 Comments

Designing combinatorial digital circuits seems like it should be easy. After all, you can do everything you want with just AND, OR, and NOT gates. Bonus points if you have an XOR gate, but you can build everything you need for combinatorial logic with just those three components. If all you want to do is design something to turn on the light when the ignition is on AND door 1 is open OR door 2 is open, you won’t have any problems. However, for more complex scenarios, how we do things has changed several times.

In the old days, you’d just design the tubes or transistor circuits you needed to develop your logic. If you were wiring up everything by hand anyway, you might as well. But then came modules like printed circuit boards. There was a certain economy to having cards that had, say, two NOR gates on a card. Then, you needed to convert all your logic to use NOR gates (or NAND gates, if that’s what you had).

Small-scale ICs changed that. It was easy to put a mix of gates on a card, although there was still some slight advantage to having cards full of the same kind of gate. Then came logic devices, which would eventually become FPGAs. They tend to have many of one kind of “cell” with plenty of logic gates on board, but not necessarily the ones you need. However, by that time, you could just tell a computer program what you wanted, and it would do the heavy lifting. That was a luxury early designers didn’t have. Continue reading “Secrets Of The Old Digital Design Titans” →

Remembering Seymour Cray

July 16, 2024 by 28 Comments

If you think of supercomputers, it is hard not to think of Seymour Cray. He built giant computers at Control Data Corporation and went on to build the famous Cray supercomputers. While those computers aren’t especially amazing today, for their time, they were modern marvels. [Asianometry] has a great history of Cray, starting with his work at ERA, which would, of course, eventually produce the computer known as the Univac 1103.

ERA was bought up by Remington Rand, which eventually became Sperry Rand. Due to conflict, some of the ERA staff left to form Control Data Corporation, and Cray went with them. The new company decided to focus on computers to do simulations for things like nuclear test simulations.

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DME With A Twist Of LimeSDR

July 16, 2024 by No comments

Navigating aircraft today isn’t like the old days. No more arrows painted on a barn roof or rotating airway beacons. Now, there are a host of radio navigation aids. GPS, of course, is available. But planes often use VOR to determine a bearing to a known point and DME — distance measuring equipment — to measure the distance to that point. DME operates around 1000 MHz and is little more than a repeater. An airplane sends a pair of pulses, and times how long it takes for the DME to repeat them. [Daniel Estévez] has been monitoring these transmissions with a LimeSDR.

Like most repeaters, the DME transponders listen on one frequency and transmit on another. Those frequencies are 63 MHz apart. This poses a challenge for some types of SDRs which have limits on bandwidth.

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