Vintage Tube Radio Restorations

[J.B. Langston] has some vintage late-40’s/early-50’s tube radios that he wanted to repair – a Motorola All-American 5 AM radio, an Air Castle AM/FM radio and a Sears Silvertone AM/FM radio. He goes over, one by one, the three vintage radios, the problems they had, and how he got them back into working order. No finding a replacement microchip here, this was all about replacing capacitors and finding vacuum tubes!

In contrast to most modern builds we see on Hackaday, vintage radios are fairly simple – mainly turret-board builds with a transformer, resistors, capacitors, coil and tubes. The main issues in any vintage electronic repair is checking the capacitors because old wax paper and electrolytic capacitors can degrade and will need replacing. When repairing the All-American 5, [J.B. Langston] had an issue with the transformer, and he goes over how he fixed what’s called silver mica disease in it. While many parts were replaced with modern equivalents, only a selenium solid-state rectifier in one of them was replaced by a different part – a silicon diode and a high-wattage series resistor.

Looking at the inside of some of these radios, it’s surprising that they could be restored at all – 65-odd years of rust, dust, dirt and grime will take their toll – but [J.B. Langston] was able to fix all three radios and clean their Bakelite cases so they look and work like new. He goes over what he discovered, how he fixed the problems and the links to where he got help when needed. We’ve seen some great vintage radio projects over the years, including adding RDS (Radio Data Systems) to a vintage radio, converting a vintage radio with modern technology and even some other radio restoration projects.

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Hollow State Receiver

[Netzener] received a Radio Shack P-Box one tube receiver as a gift. However, at the time, his construction skills were not up to the task and he never completed the project. Years later, he did complete a version of it with a few modern parts substitutions. The radio worked, but he was disappointed in its performance. Turns out, the original Radio Shack kit didn’t work so well, either. So [Netzener] did a redesign using some some old books from the 1920’s. The resulting radio–using parts you can easily buy today–works much better than the original design.

The most expensive part of the build was a 22.5V battery, which cost about $25. However, you can get away with using three 9V batteries in series if you want to save some money. The battery provides the plate voltage for the 1T4 vacuum tube. A more conventional AA battery drives the tube’s filament. Continue reading “Hollow State Receiver”

History Of The Diode

The history of the diode is a fun one as it’s rife with accidental discoveries, sometimes having to wait decades for a use for what was found. Two examples of that are our first two topics: thermionic emission and semiconductor diodes. So let’s dive in.

Vacuum Tubes/Thermionic Diodes

Our first accidental discovery was of thermionic emission, which many years later lead to the vacuum tube. Thermionic emission is basically heating a metal, or a coated metal, causing the emission of electrons from its surface.

Electroscope
Electroscope

In 1873 Frederick Guthrie had charged his electroscope positively and then brought a piece of white-hot metal near the electroscope’s terminal. The white-hot metal emitted electrons to the terminal, which of course neutralized the electroscope’s positive charge, causing the leafs to come together. A negatively charged electroscope can’t be discharged this way though, since the hot metal emits electrons only, i.e. negative charge. Thus the direction of electron flow was one-way and the earliest diode was born.

Thomas Edison independently discovered this effect in 1880 when trying to work out why the carbon-filaments in his light bulbs were often burning out at their positive-connected ends. In exploring the problem, he created a special evacuated bulb wherein he had a piece of metal connected to the positive end of the circuit and held near the filament. He found that an invisible current flowed from the filament to the metal. For this reason, thermionic emission is sometimes referred to as the Edison effect.

Thermionic diode
Thermionic diode. By Svjo [CC BY-SA 3.0], via Wikimedia Commons
But it took until 1904 for the first practical use of the effect to appear. John Ambrose Fleming had actually consulted for the Edison Electric Light Company from 1881-1891 but was now working for the Marconi Wireless Telegraph Company. In 1901 the company demonstrated the first radio transmission across the Atlantic, the letter “S” in the form or three dots in Morse code. But there was so much difficulty in telling the received signal apart from the background noise, that the result was disputed (and still is). This made Fleming realize that a more sensitive detector than the coherer they’d been using was needed. And so in 1904 he tried an Edison effect bulb. It worked well, rectifying the high frequency oscillations and passing the signals on to a galvanometer. He filed for a patent and the Fleming valve, the two element vacuum tube or thermionic diode, came into being, heralding decades of technological developments in many subsequent types of vacuum tubes.

Vacuum tubes began to be replaced in power supplies in the 1940s by selenium diodes and in the 1960s by semiconductor diodes but are still used today in high power applications. There’s also been a resurgence in their use by audiophiles and recording studios. But that’s only the start of our history.

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Simple Vacuum Tube Preamp Results in a Beautiful Build

We have no intention of wading into the vacuum tube versus silicon debates audiophiles seem to thrive on. But we know a quality build when we see it, and this gorgeous tube preamp certainly looks like it sounds good.

The amp is an attempt by builder [Timothy Cose] to give a little something back to the online community of  vacuum tube aficionados that guided him in his journey into the world of electrons under glass. Dubbed a “Muchedumbre” – Spanish for “crowd” or “mob”; we admit we don’t get the reference – the circuit is intended as a zero-gain preamp for matching impedance between line level sources and power amplifiers. Consisting of a single 12AU7 in a cathode-follower design and an EZ81 for rectification, where the amp really shines is in build quality. The aluminum and wood chassis looks great, and the point-to-point wiring is simple and neat. We especially appreciate the neatly bent component leads and the well-dressed connections on the terminal strips and octal sockets. There’s a nice photo gallery below with shots of the build.

As much as we appreciate the miracles that can be accomplished with silicon, there’s still magic aplenty with vacuum tubes. For more thermionic goodness, check out these minimalist homebrew vacuum tubes or these artisanal vacuum tubes.

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Punch Cards

Before the Commodore 64, the IBM PC, and even the Apple I, most computers took input data from a type of non-magnetic storage medium that is rarely used today: the punched card. These pieces of cardstock held programs, data, and pretty much everything used to run computers in the before-time. But with all of that paper floating around, how did a programmer or user keep up with everything? Enter the punch card sorter and [Ken Shirriff[‘s eloquent explanation of how these machines operate.

Card sorters work by reading information on the punched card and shuffling the cards into a series of stacks. As [Ken] explains, the cards can be run through the machine multiple times if they need to be sorted into more groups than the machine can manage during one run, using a radix sort algorithm.

The card reader that [Ken] examines in detail uses vacuum tubes and relays to handle the logical operation to handle memory and logic operations. This particular specimen is more than half a century old, rather robust, and a perfect piece for the Computer History Museum in Mountain View.

It’s always interesting to go back and examine (mostly) obsolete technology. There are often some things that get lost in the shuffle (so to speak). Even today, punched cards live on in the automation world, where it’s still an efficient way of programming various robots and other equipment. Another place that it lives on is in voting machines in jurisdictions where physical votes must be cast. Hanging chads, anyone?

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To See Within: Making Medical X-rays

I was a bit of a lost soul after high school.  I dabbled with electrical engineering for a semester but decided that it wasn’t for me – what I wouldn’t give for a do-over on that one. In my search for a way to make money, I stumbled upon radiologic technology – learning how to take X-rays. I figured it was a good way to combine my interests in medicine, electronics, and photography, so after a two-year course of study I got my Associates Degree, passed my boards, and earned the right to put “R.T.(R) (ARRT)” after my name.

That was about as far as that career went. There are certain realities of being in the health care business, and chief among them is that you really have to like dealing with the patients. I found that I liked the technology much more than the people, so I quickly moved on to bigger and better things. But the love of the technology never went away, so I thought I’d take a look at exactly what it takes to produce medical X-rays, and see how it’s changed from my time in the Radiology Department.

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Building Triodes With Blinker Fluid

The triode is one of the simplest kinds of vacuum tubes. Inside its evacuated glass envelope, the triode really is just a few bits of wire and metal. Triodes are able to amplify signals simply by heating a cathode, and modulating the flow of electrons to the anode with a control grid. Triodes, and their semiconductor cousin the transistor, are the basis of everything we do with electricity.

Because triodes are so fantastically simple, they’re the parts most commonly crafted by the homebrew tube artisans of today. You don’t need a glass blowing lathe to make the most basic vacuum tube, though: [Marcel] built one from the light bulb used in a car’s tail light.

The light bulb in your car’s tail light has two filaments inside: one for the normal tail light, and a second one that comes on when you brake. By burning out the dimmer filament, [Marcel] created the simplest vacuum tube device possible. In his first experiment, he turned this broken light bulb into a diode by using the disconnected filament as the anode, and the burning filament as the cathode. [Marcel] attached a 1M resistor and measured 30mV across it. It was a diode, with 30μA flowing.

The triode is just a diode with a grid, but [Marcel] couldn’t open up the light bulb to install a piece of metal. Instead, he wrapped the bulb in aluminum foil. After many attempts, [Marcel] eventually got some amplification out of his light bulb triode.

The performance is terrible – this light bulb triode actually has an “amplification” of -108dB, making it a complete waste of energy and time. It does demonstrate the concept though, even though the grid isn’t between the anode and cathode, and this light bulb is probably filled with argon. It does work in the most perverse sense of the word,  and makes for a very interesting build.