The Best Stereo Valve Amp In The World

There are few greater follies in the world of electronics than that of an electronic engineering student who has just discovered the world of hi-fi audio. I was once that electronic engineering student and here follows a tale of one of my follies. One that incidentally taught me a lot about my craft, and I am thankful to say at least did not cost me much money.

Construction more suited to 1962 than 1992.
Construction more suited to 1962 than 1992.

It must have been some time in the winter of 1991/92, and being immersed in student radio and sound-and-light I was party to an intense hi-fi arms race among the similarly afflicted. Some of my friends had rich parents or jobs on the side and could thus afford shiny amplifiers and the like, but I had neither of those and an elderly Mini to support. My only option therefore was to get creative and build my own. And since the ultimate object of audio desire a quarter century ago was a valve (tube) amp, that was what I decided to tackle.

Nowadays, building a valve amp is a surprisingly straightforward process, as there are many online suppliers who will sell you a kit of parts from the other side of the world. Transformer manufacturers produce readily available products for your HT supply and your audio output matching, so to a certain extent your choice of amp is simply a case of picking your preferred circuit and assembling it. Back then however the world of electronics had extricated itself from the world of valves a couple of decades earlier, so getting your hands on the components was something of a challenge. I cut out the power supply by using a scrap Dymar Electronics instrument enclosure which had built-in HT and heater rails ready to go, but the choice of transformers and high-voltage capacitors was something of a challenge.

Pulling the amplifier out of storage in 2017, I’m going in blind. I remember roughly what I did, but the details have been obscured by decades of other concerns. So in an odd meeting with my barely-adult self, it’s time to take a look at what I made. Where did I get it right, and just how badly did I get it wrong?

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A Tiny Sharp MZ-80K That Really Works!

If you were a computer enthusiast in the late 1970s and early 1980s, one of your objects of desire may well have been a Sharp MZ-80K. This was an all-in-one machine from the Japanese electronics giant, and like Commodore’s PET line it included a CRT monitor, full alphanumeric keyboard and cassette tape drive in a smart console.

[Yasushi Enari] is a modeller of miniatures, and while at high school back in 1981 he made a perfect 1/5 scale model of an MZ-80K as an art project. Fast-forward to 2017, and with the help of a Raspberry Pi Zero, a miniature LCD composite video screen, and a Li-Po battery, he’s turned his 1981 model into a functioning computer.

Sadly he was not able to make his tiny 1981 plastic keyboard work, so an external Bluetooth unit is required to perform that function. And he makes no mention of running an MZ-80K emulator on the little machine, either. But the result is a work of art, and an odd collaboration between his adult and teenage self, something we are guessing most readers would be proud to own.

This isn’t the first tiny replica computer we’ve shown you, an Odroid W went into making this tiny Powermac from an American Girl doll’s toy computer.

Thanks [RC2014] for the tip.

CRT Cataract Surgery

Back in the good old days, people got their information by staring into particle accelerators that could implode at any moment, and we liked it that way, by gum! To protect against disaster, CRT monitors were equipped with a safety screen laminated to the front of the tube. Decades of use often resulted in degradation of the glue used to hold the safety glass on, leading to the dread disease of “CRT cataracts.”

Luckily for aficionados of vintage terminals, [John Sutley] has come up with a cure for CRT cataracts. The video below shows the straightforward but still somewhat fussy process from start to finish. You’ll want to follow [John]’s advice on discharging the high-voltage flyback section of any stored charge; we speak from painful experience on this. With the CRT removed from the case, removing the safety screen is as simple as melting the glue with a hot air gun and applying gentle leverage with a putty knife. We’d think a plastic tool would be less likely to scratch the glass, but [John] managed to get them apart without incident. Acetone and elbow grease cleaned off the old glue, and the restored CRT looks great when reassembled.

With its cataracts cured, [John] says his next step is to restore the wonky keyboard on his Lear Siegler ADM-3A terminal. Perhaps he should look over this VT220 keyboard repair for ideas.

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Do You Have An Endangered Craft?

It is probably fair to say that as Hackaday readers, you will all be people with the ability to make things. Some of you can make incredible things, as your writers we are in constant awe of the projects that pass through our hands. But even if you feel that your skills in the maker department aren’t particularly elite, you’ll have a propensity for work in this direction or you wouldn’t be here.

Most of the craft we feature involves technologies that are still very modern indeed to the majority of the population. We for example know that the first 3D printers were built decades ago and that we take them for granted on our benches, but to the Man In The Street they are still right up there with flying cars and time-travelling police telephone boxes.

We use 3D printers and microcontrollers because they are the tools of our age, but how different might our crafts have been if we’d been born a few centuries ago? Apprenticed to a master craftsman as teenagers, we (well, at least you boys!) would have learned  a single craft to a high level of expertise, making by hand the day-to-day products of life in those times.

The Industrial Revolution brought mechanisation and mass production, and today very few of the products you use will be hand-made. There may still be a few craftsmen with the skills to produce them by hand, but in the face of the mass-produced alternative there is little business for them and they are in inevitable decline. In an effort to do something about this and save what skills remain, the Heritage Crafts Association in the UK has published a list of dying crafts, that you can view either alphabetically, or by category of risk.

It’s a list with a British flavour as you might expect from the organisation behind it, after all for example hand stitched cricket balls are not in high demand in the Americas. But it serves also as a catalogue of some fascinating crafts, as well as plenty that will undoubtedly be of interest to Hackaday readers. Making hand-made planes, saws, or spades, for example, or at least where this is being written, coracle making.

As your Hackaday scribe this is close to home, a blacksmith carrying on her father’s business can’t earn enough to live in Southern England while an electronic engineer and technical journalist can. Eventually there will be one less blacksmith plying the craft, and though his tools and some of his skills will live on here, the business will not. Take a look at the list of crafts, do any of you have them? Or do you know of any craftspeople who have any of the skills listed, that the HCA might not know about? Let us know in the comments.

Treadle lathe image: Patrick-Emil Zörner (Paddy) [CC BY-SA 2.0].

Getting Started with Blinking Lights on Old Iron

If you ever go to a computer history museum, you’ll be struck by how bland most modern computers look. Prior to 1980 computers had lights and switches, and sometimes dials and meters. Some had switchboard-like wiring panels and some even had oscilloscope-like displays. There’s something about a machine with all those switches and lights and displays that gets your hacker juices flowing. Have you ever wanted to get started in retrocomputing? Is it difficult? Do you need a lot of money? That depends on what your goals are.

There are at least three ways you can go about participating in retrocomputing: You can pony up the money to buy actual antique computers, you can build or buy old computers recreated with anywhere from zero to one hundred percent of period-authentic components, or you can experiment with emulators that run on a modern computer. As a hybrid of the second and third option there are also emulations in FPGAs.

You can see that the first option can be very expensive and you will probably have to develop a lot of repair and restoration skills. Watching [Mattis Lind] twiddle the bits on an actual PDP-8 in the clip above is great, but you’ll need to work up to it. The two techniques which get you going without the original hardware don’t have to break the bank or even cost anything presuming you already have a PC.

Although some sneer at emulation, for some machines it is almost the only way to go. You couldn’t buy the original EDSAC, for example. It is also a good way to get started without a lot of expense or risk. But regardless of how you do it, there’s one thing in common: you have to know how to operate the thing.

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DIY VT220 Keyboard

There’s always been interest in the computers of old, and people love collecting and restoring them. When [peterbjornx] got his hands on a DEC VT220 video terminal, it was in good shape – it needed a bit of cleaning, but it also needed a keyboard. [Peter] couldn’t afford to buy the keyboard, but the service manual for it was available, so he decided to convert a modern keyboard to work with his new terminal.

The original keyboard for the VT220 is the LK201. This keyboard communicates with the terminal using 8-N-1 (eight data bits, no parity, one stop bit) over RS232 at 4800 baud. This meant that it would be pretty simple to implement this on microcontroller in order to communicate with the terminal. [Peter] chose the Arduino Nano. However, the LK200 was more than just a keyboard for communicating with the terminal, it also housed a speaker and LEDs which the terminal used to communicate with the user. Rather than put these into the adapter unit, [Peter] decided to put these into the keyboard – a few holes and a bit of wiring, and they were in.

[Peter]’s write-up includes a description of some of the issues he encountered as well as a picture of the keyboard. He’s put the schematic online and the code up on GitHub. In case you were wondering, he used Vim on the VT220 to write his article. You could also use a Raspberry Pi to help out your dumb terminal, or just hook the terminal directly to your Linux box and go from there.

A New Battery For A Potted Clock Module

If you did much dismantling of PCs back in the 1980s and 1990s, you might be familiar with the Dallas Semiconductor range of potted real-time clock modules. These were chunky dual-in-line devices containing clock and non-volatile RAM chips, a crystal, and a lithium battery. The battery was good for about a decade, which was fine for most PCs of the day because the majority of desktop computers are replaced long before that deadline.

[Glitch], however has an industrial single-board computer with a 486 processor that has had a life much more prolonged than its desktop siblings due to its application. The battery in the onboard Dallas DS1387 has long ago expired, and since these devices are so long out of production to be unavailable, he’s had to improvise.

Improving on some previous documented projects he found through an internet search, he carefully ground away the potting compound to reveal a couple of the battery conductors, cut them with a PCB drill, and mounted a lithium cell holder on the top of the device with some tidily soldered Kynar wires to bring in the power. A CR1225 cell was used rather than the ubiquitous CR2032, as space was at a premium in the width of the ISA card form factor.

The potted RTC module is something of a rare device these days, but if you have a retro computer containing one this seems to be a very useful piece of work to bring it back to life. We’ve covered another similar one with a slightly larger battery in the past.