classic hacks

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A Cake Tin Makes A Great Tube Amp Chassis

June 5, 2016 by 44 Comments

If you have ever had a go at building a tube-based project you will probably be familiar with the amount of metalwork required to provide support structures for the tubes themselves and the various heavy transformers and large electrolytic capacitors. Electronic construction sixty years ago was as much about building the chassis of a project as it was about building the project itself, and it was thus not uncommon to see creative re-use of a chassis salvaged from another piece of equipment.

This morning we stumbled upon a rather nice solution to some of the metalwork woes facing the tube constructor courtesy of [Bruce], who built his tube audio amplifier on a chassis made from a cake tin and with its transformers housed in decorative display tins.

The circuit itself is a straightforward single-ended design using an ECL82 triode-pentode on each stereo channel, and comes courtesy of [Nitin William]. The power supply is on-board, and uses a pair of silicon diodes rather than another tube as the rectifier.

It’s true that [Bruce] has not entirely escaped metalwork, he’s still had to create the holes for his tubes and various mountings for other components. But a lot of the hard work in making a tube chassis is taken care of with the cake tin design, and the result looks rather professional.

We have something of a personal interest in single-ended tube amplifiers here at Hackaday, as more than one of us have one in our constructional past, present, or immediate futures. They are a great way to dip your toe in the water of tube amplifier design, being fairly simple and easy to make without breaking the bank. We’ve certainly featured our share of tube projects here over the years, for example our “Groove tube” round-up, or our look at some alternative audio amplifiers.

How An Amiga Graphics Business Ran In The 1990s

June 5, 2016 by 37 Comments

If you have ever used an eraser to correct a piece of pencil work, have you ever considered how much of an innovation it must have seemed when the first erasers were invented? It might seem odd to consider a centuries-old piece of stationery here on Hackaday, but there is a parallel in our own time. Digital image manipulation is such a part of everyday life these days as to have become run-of-the-mill for anyone with a mobile phone and the right app, but it’s easy to forget how recent an innovation it really is. Only a few decades ago your only chance of manipulating a photograph was to spend a lot of time in a darkroom with a photographic developer of exceptional skill, now children who have never known a world in which it wasn’t possible can manipulate their selfies with a few deft touches of the screen.

[Steve Greenfield] pointed us at a detailed description of the business he ran in the 1990s, offering digital and composite photography using an upgraded Amiga 3000.  It caught our attention as a snapshot of the state of digital image manipulation when these things still lay at the bleeding edge of what was possible.

His 3000 was highly customised from the stock machine. It featured a Phase 5 68060 accelerator board, a Cybervision 64 graphics card, a then-unimaginably-huge 128MB RAM, and an array of gigabyte-plus Fast SCSI drives.  To that he had attached a Polaroid SCSI digital camera with a then-impressive 800×600 pixel resolution. The Polaroid had no Amiga drivers, so he ran the Shapeshifter Mac emulator to capture images under the MacOS of the day. The fastest 68000-series Mac only had a 68040 which the early PowerPC Macs could only emulate, so he writes that his 68060-equipped Amiga ran the Mac software faster than any Mac at the time.

His stock-in-trade was attending sci-fi conventions and giving costumed attendees pictures with custom backgrounds, something of a doddle on such a souped-up Amiga. He writes of the shock of some Microsoft employees on discovering a 60MHz computer could run rings round their several-hundred-MHz Pentiums running Windows 95.

His business is long gone, but its website remains as a time capsule of the state of digital imagery two decades ago. The sample images are very much of their time, but for those used to today’s slicker presentation it’s worth remembering that all of this was very new indeed.

In a world dominated by a monoculture of Intel based desktop computers it’s interesting to look back to a time when there was a genuine array of choices and some of them could really compete. As a consumer at the start of the 1990s you could buy a PC or a Mac, but Commodore’s Amiga, Atari’s ST, and (if you were British) Acorn’s ARM-based Archimedes all offered alternatives with similar performance and their own special abilities. Each of those machines still has its diehard enthusiasts who will fill you in with a lengthy tale of what-if stories of greatness denied, but maybe such casualties are best viewed as an essential part of the evolutionary process. Perhaps the famous Amiga easter egg says it best, “We made Amiga … ”

Here at Hackaday we’ve covered quite a few Amiga topics over the years, including another look at the Amiga graphics world. It’s still a scene inspiring hardware hackers, for example with this FPGA-based Amiga GPU.

Amiga 3000 image: By [Joe Smith] [Public domain], via Wikimedia Commons.

How Does A Buck Converter Work Anyway?

June 4, 2016 by 30 Comments

[Great Scott] should win an award for quickest explanation of a buck converter. Clocking in at five and a half minutes, the video clearly shows the operating principles behind the device.

It starts off with the question, what should you do if you want to drop a voltage? Many of us know that we can dim and brighten an LED using the PWM on an Arduino, but a closer inspection with an oscilloscope still shows 5V peaks that would be dangerous to a 3.3V circuit. He then adds an inductor and diode, this keeps the current from dropping too fast, but the PWM just isn’t switching fast enough to keep the coil energized.

A small modification to the Arduino’s code, and the PWM frequency is now in the kHz range. The voltage looks pretty good on the oscilloscope, but a filter cap gets it to look nice and smooth. Lastly, he shows how when the load changes the voltage out looks different. To fix this a voltage divider feeds back the information to the Arduino, letting it change the PWM duty to match the load.

In the last minute of the video he shows how to hook up off-the-shelf switching regulators, whose support components are now completely demystified as the basic principles are understood. Video after the break.

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Greet The Sun With A 555 Flute

June 3, 2016 by 6 Comments

Here’s an interesting implementation of a classic: the 555 timer as astable multivibrator for the noble purpose of making weird music. [pratchel] calls this a Morgenflöte or morning flute, indicating that it is best played in the morning. It would certainly wake up everyone in the house.

Instead of using LDRs in straight-up Theremin mode and waving his hands about, [pratchel] mounted one in each of several cardboard tubes. One tube is small and has just a few holes; this is intended to be used as a flute. [pratchel] cautions against locating holes too close to the LDR, because it will overpower the others when left uncovered. A larger tube with more holes can be used as a kind of light-dependent slide whistle with another holey tube that fits inside. We were disappointed to find that the giant tube sitting by the amplifier hasn’t been made into a contrabass flute.

Continuing the theme of astability, [pratchel] went completely solderless and built the circuit on a breadboard. The LDR’s legs are kept separate by a piece of cardboard. This kind of project and construction is fairly kid and beginner-friendly. It would be a good one for getting your musically inclined friends and family members into electronics. Here’s a 555 player piano built by Hackaday’s own [Steven Dufresne] that might be a good second step. Check out [pratchel]’s performance after the break.

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Retrotechtacular: Fog Over Portland

June 1, 2016 by 23 Comments

In the early days of broadcast television, national spectrum regulators struggled to reconcile the relatively huge bandwidth required by the new medium with the limited radio spectrum that could be allocated for it. In the USA during the years immediately following World War Two there was only a 12-channel VHF allocation, which due to the constraints of avoiding interference between adjacent stations led to an insufficient number of possible transmitter sites to cover the entire country. This led the FCC in 1949 to impose a freeze on issuing licences for new transmitters, and left a significant number of American cities unable to catch their I Love Lucy or The Roy Rogers Show episodes.

The solution sought by the FCC was found by releasing a large block of UHF frequencies between 470 and 890 MHz from their wartime military allocation, and thus creating the new channels 14 to 83. An experimental UHF pilot station was set up in Bridgeport, Connecticut in 1949, and by 1952 the FCC was ready to release the freeze on new licence applications. The first American UHF station to go on air was thus KPTV in Portland, Oregon, on September 18th of that year.

UHF TV was a very new technology in 1952, and was close to the edge of what could be achieved through early 1950s consumer electronics. Though the 525-line TV standard and thus the main part of the sets were the same as their VHF counterparts, the tuner designs of the time could not deliver the performance you might expect from more recent sets. Their noise levels, sensitivity, and image rejection characteristics meant that UHF TV reception  did not live up to some of its promise, and thus a fierce battle erupted between manufacturers all keen to demonstrate the inferiority of their competitors’ products over the new medium.

The video below the break delivers a fascinating insight into this world of claim and counter-claim in 1950s consumer electronics, as Zenith, one of the major players, fires salvos into the fray to demonstrate the superiority of their products over competing models or UHF converters for VHF sets. It’s very much from the view of one manufacturer and don’t blame us if it engenders in the viewer a curious desire to run out and buy a 1950s Zenith TV set, but it’s nonetheless worth watching.

A key plank of the Zenith argument concerns their turret tuner. The turret tuner was a channel selection device that switched the set’s RF front end between banks of coils and other components each preset to a particular TV channel. Zenith’s design had a unique selling point that it could be fitted with banks of components for UHF as well as VHF channels thus removing the need for a separate UHF tuner, and furthermore this system was compatible with older Zenith sets so existing owners had no need to upgrade. Particularly of its time in the video in light of today’s electronics is the section demonstrating the clear advantages of Zenith’s germanium mixer diode over its silicon equivalent. Undeniably true in that narrow application using the components of the day, but not something you hear often.

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Kerbal Space Program For The Apple II

May 31, 2016 by 14 Comments

[Vince Weaver] tried to use his time machine to jump a few years in the future to get a less buggy version of Kerbal Space Program, but as usual with time travel, nothing went right and he ended up heading to 1987. Finding himself in an alternate timeline where KSP had been released for the Apple II, he brought back a copy.

Well, that’s the narrative proposed by [Vince Weaver] on his YouTube channel. The real story, and hack, being that he wrote a version of KSP for the Apple II in Applesoft Basic. He has used the language for the ridiculous before. You can build a rocket, select a pilot, launch, and if you’re lucky (or skilled), reach orbit.

We loaded up his disk image on an Apple II emulator and gave it a try. We managed to murde—lose a few pilots, but that was about it.  It was hard not to get distracted by the graphics and remember to point the rocket the right direction. Either way, it was a neat bit of fun in retro computing. Video after the break.

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Hackaday Prize Entries: Inventing New Logic Families

May 30, 2016 by 46 Comments

One of the favorite pastimes of electronics hobbyists is clock making. Clocks are a simple enough concept with a well-defined goal, but it’s the implementation that matters. If you want to build a clock powered only by tubes and mains voltage, that’s a great skill tester. A relay-based timepiece is equally cool, and everyone should build a Nixie tube clock once in their lives.

For [Ted]’s Hackaday Prize entry, he’s building a clock. Usually, this would be little cause for celebration, but this is not like any clock you’ve ever seen. [Ted] is building this clock using only diodes, and he’s inventing new logic families to do it.

Using diodes as logic elements has been around since the first computers, but these computers had a few transistors thrown in. While it is possible to make AND and OR gates using only diodes, a universal logic gate – NANDs and NORs – are impossible. For the computers of the 1950s, that means tubes or transistors and DTL logic.

For the past few years, [Ted] has been working on a diode-only logic family, and it appears he’s solved the problem. The new logic family includes a NOR gate constructed using only diodes, resistors, and inductors. The key design feature of these gates is a single diode to switch an RF power supply on and off. It relies on an undocumented property of the diodes, but it does work.

Although [Ted] can create a NOR gate without transistors — a feat never before documented in the history of electronics — that doesn’t mean this is a useful alternative to transistor logic. The fan-out of the gates is terrible, the clock uses about 60 Watts, and the gates require an AC power supply. While it is theoretically possible to build a computer out of these gates, it’s doubtful if anyone has the patience to do so. It’s more of a curiosity, but it is a demonstration of one of the most mind-bending projects we’ve ever seen.

You can check out a video of the diode clock below.

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