Op Amps Before Transistors: A 600V Vacuum Tube Monster

Op amps. Often the first thing that many learn about when beginning the journey into analog electronics, they’re used in countless ways in an overwhelmingly large array of circuits. When we think about op amps, images of DIPs and SOICs spring to mind, with an incredibly tiny price tag to boot. We take their abundance and convenience for granted nowadays, but they weren’t always so easy to come by.

[Mr Carlson] serves up another vintage offering, this time in the form of a tube op amp. The K2-W model he acquired enjoyed popularity when it was released as one of the first modular general purpose amplifiers, due to its ‘compact form’ and ‘low price’. It also came with large application manuals which helped it to gain users.

In order to power up the op amp and check its functionality, +300V and -300V supplies are needed. [Mr Carlson] is able to cobble something together, since it’s very apparent that he has an enviable stash of gear lying around. A 600V rail to rail supply is not something to be taken lightly, though it does give this particular model the ability to output 100V pk-pk without any distortion.

The op amp is set up as an inverting amplifier, and once powered on proves to work flawlessly. As always, the video is an entertaining watch, stuffed full of retro electronics trivia. We’re big fans of [Mr Carlson]’s work, and have previously written about his adventures with a colossal walk-in AM radio transmitter, as well as his restoration of a 1930s oscilloscope and subsequent transformer de-potting.

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A Stereo Tube Amp For Less Than $5

Many of us have aspirations of owning a tube amp. Regardless of the debate on whether or not tube audio is nicer to listen to, or even if you can hear the difference at all, they’re gorgeous to look at. However, the price of buying one to find out if it floats your boat is often too high to justify a purchase.

A motor transformer

[The Post Apocalyptic Inventor] has built a stereo tube amplifier in the style of the Fallout video games. The idea came when he realised that the TK 125 tape recorder manufactured by Grundig was still using tube audio in the late 60s. What’s more, they frequently sell on eBay for 1-10€ in Germany. [TPAI] was able to salvage the main power amplifier from one of these models, and restore it so that it could be re-purposed and see use once more.

The teardown of the original cassette recorder yields some interesting parts. Firstly, an integrated motor transformer — an induction motor whose stator acts as the magnetic core of the transformer responsible for the tube electronics. There’s also an integrated capacitor which contains three separate electrolytics. The video after the break is well worth a watch (we always find [TPAI]’s videos entertaining).

A new chassis is created out of a steel base plate and aluminium angle, and some neat frames for the motor transformers are made from scrap copper wire bent and soldered together. It looks great, though there’s always the option to use a cake tin instead.

If you’re interested in the design of tube amps, we’ve covered heaps of cool builds: from this low-voltage design to this tiny guitar amp, or even ones using tubes which are flat.

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Raytheon’s Analog Read-Only Memory is Tube-Based

There are many ways of storing data in a computer’s memory, and not all of them allow the computer to write to it. For older equipment, this was often a physical limitation to the hardware itself. It’s easier and cheaper for some memory to be read-only, but if you go back really far you reach a time before even ROMs were widespread. One fascinating memory scheme is this example using a vacuum tube that stores the characters needed for a display.

[eric] over at TubeTime recently came across a Raytheon monoscope from days of yore and started figuring out how it works. The device is essentially a character display in an oscilloscope-like CRT package, but the way that it displays the characters is an interesting walk through history. The monoscope has two circuits, one which selects the character and the other determines the position on the screen. Each circuit is fed a delightfully analog sine wave, which allows the device to create essentially a scanning pattern on the screen for refreshing the display.

[eric] goes into a lot of detail on how this c.1967 device works, and it’s interesting to see how engineers were able to get working memory with their relatively limited toolset. One of the nice things about working in the analog world, though, is that it’s relatively easy to figure out how things work and start using them for all kinds of other purposes, like old analog UHF TV tuners.

Oddball Mercury Vapor Rectifier Is A Tube Geek’s Delight

Even if you aren’t a tube aficionado, you can’t help but be mesmerized by the blue glow inside a mercury vapor rectifier when it operates. It looks less like early 20th century tech and more like something that belongs on a Star Trek set. [Uniservo] acquired an 866 rectifier that was interesting due to the markings, which he explains in detail in the video below. Most people though will probably want to skip to closer to its end to see that distinctive blue glow. The exact hue depends on the mercury vapor pressure and usually contains a fair amount of ultraviolet light.

These tubes have an interesting history dating back to 1901, the year [Peter Cooper Hewitt] developed a mercury vapor light which was much more efficient than conventional bulbs. They had two main problems, they required some special process to get the mercury inside to vaporize when you turned them on, but worse still, the light was blue-green which isn’t really appropriate for home and office lighting. In 1902 though, [Hewitt] realized the tube would act as a rectifier. Electrons could readily flow out of the mercury vapor that was the cathode, while the carbon anodes didn’t give up electrons as readily. This was important because up until then, there wasn’t an easy way to convert AC to DC. The usual method was to use an AC motor coupled to a DC generator or a similar mechanical arrangement known as a rotary converter.

In later decades the mercury vapor lamp would wind up with a phosphor coating that converted the ultraviolet light to cool white light and became the fluorescent bulb, so while the rectifier mostly gave way to more efficient methods, [Hewitt’s] bulb has been in use for many years.

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Adventures In Gas Filled Tube Arrays

Vacuum tubes are awesome, and Nixies are even better. Numitrons are the new hotness, but there’s one type of tube out there that’s better than all the rest. It’s the ИГГ1-64/64M. This is a panel of tubes in a 64 by 64 grid, some with just green dots, some with green and orange, and even a red, green, blue 64 by 64 pixel matrix. They’re either phosphors or gas-filled tubes, but this is the king of all tube-based displays. Not even the RGB CRTs in a Jumbotron can match the absurdity of this tube array.

[Muth] got his hands on a few of these panels, and finally he’s displaying images on them. It’s an amazing project that involved finding the documentation, translating it, driving the tubes with 360 Volts, and figuring out a way to drive 128 inputs from just a few microcontroller pins.

First, the power supply. These panels require about 360 Volts to light up. This is significantly higher than what would usually be found in a Nixie clock or other normal tube-based display. That’s no problem, because a careful reading of the datasheet revealed a circuit that brings a normal-ish 180 Volt Nixie power supply up to the proper voltage. To drive these pixels, [Muth] settled on a rather large PIC18F microcontroller with eight tri-state buffers. The microcontroller takes data over a serial port and scans through the entire framebuffer. All in all, there are eight driver boards, 736 components, and 160 wires connecting everything together. It’s a lot of work, but now [Muth] has a 64×64 display that’s green and orange.

You can check out a ‘pixel dust’ demo of this display in action below.

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Addition on the Strangest Vacuum Tube

[Uniservo] made a video of a tube he’s been trying to acquire for a long time: a Rogers 6047 additron. Never heard of an additron? We hadn’t either. But it was a full binary adder in a single vacuum tube made in Canada around 1950. You can see the video below.

The unique tubes were made for the University of Toronto Electronic Computer (UTEC). A normal tube-based computer would require several tubes to perform an addition, but the additron was a single tube that used beam switching to perform the addition in a single package. [Uniservo] points out how the tube could have revolutionized tube computing, but before it could really appear in real designs, transistors — and later, integrated circuits — would take over.

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Slimline Nixie Clocks

Everyone needs to build a Nixie clock at some point. It’s a fantastic learning opportunity; not only do you get to play around with high voltages and tooobs, but there’s also the joy of sourcing obsolete components and figuring out the mechanical side of electronic design as well. [wouterdevinck] recently took up the challenge of building a Nixie clock. Instead of building a clock with a huge base, garish RGB LEDs, and other unnecessary accouterments, [wouter] is building a minimalist clock. It’s slimline, and a work of art.

The circuit for this Nixie clock is more or less what you would expect for a neon display project designed in the last few years. The microcontroller is an ATMega328, with a Maxim DS3231 real time clock providing the time. The tubes are standard Russian IN-14 Nixies with two IN-3 neon bulbs for the colons. The drivers are two HV5622 high voltage shift registers, and the power supply is a standard, off-the-shelf DC to DC module that converts 5 V from a USB connector into the 170 V DC the tubes require.

The trick here is the design. The electronics for this clock were designed to fit in a thin base crafted out of sheets of bamboo plywood. The base is a stackup of three 3.2mm thick sheets of plywood and a single 1.6 mm piece that is machined on a small desktop CNC.

Discounting the wristwatch, this is one of the thinnest Nixie clocks we’ve ever seen and looks absolutely fantastic. You can check out the video of the clock in action below, or peruse the circuit design and code for the clock here.

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