Hackaday Prize Entry: Hot Logic

A few weeks ago, [Yann] was dumpster diving and found something of interest. Two vacuum tubes, an ECC83S and an EL84. This was obviously the droppings of a local guitarist, but [Yann] wanted to know if he could build something useful out of them. An amplifier is far too pedestrian, so he settled on a vacuum tube computer.

The normal pentodes and triodes you’ll find in a tube amp require a lot of support components like output transformers, tube sockets, and high voltage power supplies. This was a little too complicated for a tube computer, but after a little bit of searching, [Yann] found a better option for his MINIVAC — subminiature vacuum tubes. These require fewer support components, and can be found for very reasonable prices through the usual component suppliers. His entry for this year’s Hackaday Prize is Hot Logic. It’s a computer — or at least computer components — built out of these tubes.

The tubes in question are a few 1Ж29Б-В and 6Н21Б tubes, a vacuum pentode and dual triode, respectively. Add in a few diodes, and that meets the requirements for being sufficient to build a computer. As a neat little bonus, these tubes have requirements that are very easy to meet. The filament on the 1Ж29Б-В tube only needs 1.2 Volts.

These subminiature tubes are a little underappreciated in the world of audiophililia and DIY electronics. That’s a bit of a shame; these tubes are the most technologically advanced vacuum-based technology ever created. They were the heart and the brains of ballistic missiles, and if you look hard enough you source hundreds of them at very reasonable prices. A vacuum tube computer requires a lot of tubes, and if anyone will be able to build a vacuum tube computer it’s going to be [Yann] and his pile of Soviet surplus.

Resurrection — Pressing WW2 Radio Equipment Back into Service

Mass production was key to survival during the Second World War. So much stuff was made that there continues to be volumes of new unpacked stuff left over and tons of used equipment for sale at reasonable prices. Availability of this war surplus provided experimenters in the mid 20th century with access to high performance test equipment, radio equipment, and high quality components for the first time.

Even today this old stuff continues to motivate and inspire the young generations because of its high build quality, unique electro-mechanical approaches, and overall innovative designs which continue to be relevant into the 21st century. In this post we will show you how to get started in the hobby of resurrecting WW2 radio equipment and putting it back on the air.

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Home Brew Vacuum Tubes Are Easier Than You Think

It all began with a cheap Chinese rotary vane vacuum pump and a desire to learn the witchcraft of DIY vacuum tubes. It ended with a string of successes – a working vacuum chamber, light bulbs, glow tubes, diodes, and eventually this homebrew power triode and the audio amplifier built around it.

[Simplifier]’s workshop seems like a pretty cool place. It must have a bit of an early 20th-century vibe, like the shop that [John Fleming] used for his early work on vacuum tubes. Glass work, metal work, electronics – looks like [Simplifier] has a little bit of everything going on. True to his handle, once [Simplifier] had a cheap but effective vacuum rig he started with the easiest projects – incandescent and gas discharge lamps. Satisfied that he could make solid electrical and physical connections and evacuate the tubes, he moved on to diodes and eventually triodes. The quality of the tubes is pretty impressive – stray gasses are removed with a bake-out oven and induction-heated titanium getters. And the performance is pretty solid, as the video below reveals.

Very impressive overall, and it’s not just the fact that he’s building tubes from scratch – we’ve seen that before. What shines here is that specialized equipment is not needed to make working and reliable tubes – just a MAPP torch, simple hand tools, and a low-end vacuum rig. Anybody could – and probably should – give this a try.

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Flying Close To The Flame: Designing Past Specified Limits

A very good question came up on The EEVBlog forum that I thought deserved an in depth answer. The poster asked why would amplifier companies in the heyday of tube technology operate tubes in mass produced circuits well in excess of their published manufacturers recommended limits. The simple answer is: because the could get away with it. So the real question worth exploring is how did they get away with operating outside of their own published limitations? Let’s jump in and take a look at the collection of reasons.

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Alfred P. Morgan: A Generation’s Radio Hacker

I was surfing the web looking for interesting projects the other day when I ran into [SkyKing’s] exquisite transistor demodulator radio builds. He mentioned that they were “Alfred P. Morgan-style” and that brought back a flood of memories about a man who introduced a whole generation to electronics and radio.

[Morgan] was born in 1889 and in the early part of the twentieth century, he was excited to build and fly an airplane. Apparently, there wasn’t a successful flight. However, he eventually succeeded and wrote his first book: “How to Build a 20-foot Bi-Plane Glider.” In 1910, he and a partner formed the Adams Morgan company to distribute radio construction kits. We probably wouldn’t remember [Morgan] for his airplanes, but we do recognize him for his work with radio.

By 1913, he published a book “The Boy Electrician” which covered the fundamentals of electricity and magnetism (at a time when these subjects were far more mysterious than they are today). [Morgan] predicted the hacker in the preface to the 1947 edition. After describing how a boy was frustrated that his model train automated to the point that he had nothing actually to do, [Morgan] observed:

The prime instinct of almost any boy at play is to make and to create. He will make things of such materials as he has at hand, and use the whole force of dream and fancy to create something out of nothing.

Of course, we know this applies to girls too, but [Morgan] wrote this in 1913, so you have to fill in the blanks. I think we can all identify with that sentiment, though.

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Retrotechtacular: The Hammond Novachord

Just when we thought we’d heard of all the cool early synthesizers, a tipster rattled our jar with news that someone completely restored a Novachord. These spinet piano-shaped prototypical synthesizers were made by Hammond for only four years. About a thousand of them were built before sales sagged and parts became scarce in 1942. It is estimated that only 200 or so are still around today.

The Novachord’s sounds are generated by a bank of twelve monostable vacuum tube oscillators. Each one is tuned to a pitch of the chromatic scale in what is called divide-down architecture. [Hammond] and his co-creators [John Hanert] and [C.N. Williams] used the property of dividing a frequency in half to generate the same tone, but one octave lower. This design means that all 72 notes can be played at the same time. Adjustable formant filters shape the often otherworldly sounds, which are then passed through flexible tube-based envelopes.

[Phil] knew it would be a big job to restore a Novachord in any condition. Thousands of passive components all had to be replaced. The cabinet bore all the hallmarks of a well-used parlor instrument—water rings from cocktails, scratches, and cigarette burns galore. [Phil] says that woodworking really isn’t his thing, but he did an outstanding job nonetheless of sanding every nook and cranny and applying several coats of stain. There are tons of drool-inducing pictures on his project site, and several clips of [Phil] really putting it through its paces.

Thanks for the tip, [Mike]!

Retrotechtacular is a weekly column featuring hacks, technology, and kitsch from ages of yore. Help keep it fresh by sending in your ideas for future installments.

Artisanal Vacuum Tubes: Hackaday Shows You How

Homemade Vacuum Tube
Homemade Vacuum Tube

About a decade ago I started a strange little journey in my free time that cut a path across electronics manufacturing from over the last century. One morning I decided to find out how the little glowing glass bottles we sometimes call electron tubes worked. Not knowing any better I simply picked up an old copy of the Thomas Register. For those of you generally under 40 that was our version of Google, and resembled a set of 10 yellow pages.

I started calling companies listed under “Electron Tube Manufacturers” until I got a voice on the other end. Most of the numbers would ring to the familiar “this number is no longer in service” message, but in one lucky case I found I was talking to a Mrs. Roni Elsbury, nee Ulmer of M.U. Inc. Her company is one of the only remaining firms still engaged in the production of traditional style vacuum tubes in the U.S. Ever since then I have enjoyed occasional journeys down to her facility to assist her in maintenance of the equipment, work on tooling, and help to solve little engineering challenges that keep this very artisanal process alive. It did not take too many of these trips to realize that this could be distilled down to some very basic tools and processes that could be reproduced in your average garage and that positive, all be it rudimentary results could be had with information widely available on the Internet.

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