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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Biasing That Transistor: The Common Base Amplifier

We’ve previously remarked upon a generation lucky enough to be well-versed in microcontrollers and computersised electronics through being brought up on the Arduino or the Raspberry Pi but unlucky enough to have missed out on basic electronics such as how to bias a transistor, and to address that gap we’ve taken a look at the basics of transistor biasing.

All the circuits we worked with in the previous article had the transistor’s emitter taken to ground, took their input from the base, and their output from the collector. This configuration, called a Common Emitter amplifier is probably the most common, but it is far from the only way to use a transistor. Once you have set up the bias voltage as we described to the point at which the transistor is in its linear region, there are several other ways in which the device can be used as an amplifier. The subject of this article is one of these configurations, so described because it takes the transistor’s base to the ground instead of the emitter, as a Common Base amplifier. Continue reading “Biasing That Transistor: The Common Base Amplifier”

Won’t Somebody, Please, Think Of The Transistors!

At what age did you begin learning about electronics? What was the state of the art available to you at the time and what kinds of things were you building? For each reader these answers can be wildly different. Our technology advances so quickly that each successive generation has a profoundly different learning experience. This makes it really hard to figure out what basic knowledge today will be most useful tomorrow.

Go on, guess the diode!
Go on, guess the diode!

Do you know the forward voltage drop of a diode? Of course you do. Somewhere just below 0.7 volts, give or take a few millivolts, of course given that it is a silicon diode. If you send current through a 1N4148, you can be pretty certain that the cathode voltage will be that figure below the anode, every time. You probably also have a working knowledge that a germanium diode or a Schottky diode will have a lower forward voltage, and you’ll know in turn that a bipolar transistor will begin to turn on when the voltage between its base and emitter achieves that value. If you know Ohm’s Law, you can now set up a biasing network and without too many problems construct a transistor amplifier.

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42,300 Transistor Megaprocessor Is Complete

As it turns out, the answer is not 42, it’s 42.3 — thousand. That’s how many discrete transistors spread across the 30 m2 room housing this massive computation machine. [James Newman’s] Megaprocessor, a seriously enlarged version of a microprocessor, is a project we’ve been following with awe as it took shape over the last couple of years.

[James] documented his work in great detail, and by doing so, took us on a journey through the inner workings of microprocessors. His monumental machine is now finished, and it’s the ultimate answer to how a processor – and pretty much everything that contains a processor – works.

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How The Dis-integrated 6502 Came To Be

I made a bee line for one booth in particular at this year’s Bay Area Maker Faire; our friend [Eric Schlaepfer] had his MOnSter 6502 on display. If you missed it last week, the unveiling of a 6502 built from discrete transistors lit the Internet afire. At that point, the board was not fully operational but [Eric’s] perseverance paid off because it had no problem whatsoever blinking out verification code at his booth.

I interviewed [Eric] in the video below about the design process. It’s not surprising to hear that he was initially trying to prove that this couldn’t be done. Unable to do so, there was nothing left to do but devote almost six-months of his free time to completing the design, layout, and assembly.

What I’m most impressed about (besides just pulling it off in the first place) is the level of perfection [Eric] achieved in his design. He has virtually no errors whatsoever. In the video you’ll hear him discuss an issue with pull-up/pull-down components which did smoke some of the transistors. The solution is an in-line resistor on each of the replacement transistors. This was difficult to photograph but you can make out the soldering trick above where the 3-pin MOSFET is propped up with it’s pair of legs on the board, and the single leg in the air. The added resistor to fix the issue connects that airborne leg to its PCB pad. Other than this, there was no other routing to correct. Incredible.

The huge schematic binder includes a centerfold — literally. One of the most difficult pieces of the puzzle was working out the decode ROM. What folds out of this binder doesn’t even look like a schematic at first glance, but take a closer look (warning, 8 MB image). Every component in that grid was placed manually.

I had been expecting to see some tube-based goodness from [Eric] this year. That’s because I loved his work on Flappy Bird on a green CRT in 2014, and Battlezone on a tube with a hand-wound yoke last year. But I’m glad he stepped away from the tubes and created this marvelous specimen of engineering.

Review: Transistor Tester

Amazon has been getting creepier and creepier lately with their recommendations.  Every time I log in, I’m presented with a list of new Blinky LEDs, Raspberry Pi accessories, Arduino shields, and the like. It’s as if they know me. Their customer database paid off when it recommended a $22 transistor / component tester. I’ve been seeing those testers around quite a bit lately. Curiosity got the better of me and my mouse found its way to the “Buy it now with one click” button. Two days later I had a “SainSmart Mega328 Transistor Tester Diode Triode Capacitance ESR Meter MOS/PNP/NPN L/C/R” in my hands.

I’m going to get the obvious out of the way. This thing is built cheap – as cheap as the factories can make it. My particular unit arrived with the LCD flapping in the breeze, hanging on by its flex cable. Fitting the LCD back into the acrylic backlight frame revealed a slightly worrisome twist in that same flex. Thankfully nothing was actually damaged, though I do want to give the flex cable some protection in the future. More on that later. The circuitry was open for all the world to see on the bottom of the tester. The heart of the unit is an ATmega328. Supporting it are a few transistors and a handful of passives.

I didn’t have huge expectations for the tester, but I hoped it would at least power up.  Hooking up a 9 volt battery and pressing the magic button brought the tester to life. Since I didn’t have anything in the socket, it quickly lit up and displayed its maker information – “91make.taobao.com”, and “By Efan & HaoQixin”, then it informed me that I had “No, unknown, or damaged part”.

I had a few resistors lying around the bench (doesn’t everyone?) so I put one in. The tester read it as 9881 ohms. Sure enough, it was a 10K 5% resistor.  Capacitors – ceramic disc, electrolytic, and surface mount all worked as well. The tester even provided ESR values. The real test would be a transistor. I pulled an old  2N2222 in a TO-18 metal can, and popped it in the tester. The damn thing worked – it showed the schematic symbol for an NPN transistor with Collector, Base, and Emitter connected to Pins 1,2,and 3 respectively. Flipping the pins around and re-testing worked as well. The tester showed hFe as 216, and forward voltage as 692 mV, both reasonable numbers for a 2N2222.

triacThe tester worked surprisingly well – it was able to correctly identify BJTs, FETs, even esoteric parts. The only thing it balked on was a linear voltage regulator, which showed up as two diodes. Regulators are a bit more than a simple device though, so I can’t blame the tester there.  The values returned were all reasonable as well. While I don’t have a calibrated lab to check against, the numbers lined up with my Fluke meter.

So what exactly is driving this little tester? There are about 20 versions of it on the market, all of them from China. 91make is a seller on taobao.com, often referred to as “China’s ebay.” 91make’s front page features no less than 7 versions of the transistor tester, with various cases and LCDs. Some digging turned up the history on this device. It turns out the transistor tester is an open source hardware project (translated) originally created by [Markus Frejek], and built upon by [Karl-Heinz Kubbeler] and a number of others. The Subversion repository  for the project shows it is quite active, with the most recent check-in only a few hours ago. The project is also well documented. The English PDF is 103 pages, explaining theory of operation, the circuit itself, and the software. The document even explains some of the shortcomings of the Chinese versions of the tester, including using a zener diode where the original schematic calls for a precision 2.5V reference. Yes, it will work, but it won’t be as accurate as the original.

The devs also don’t officially support the clones which I can understand, considering the quality and changes in design each manufacturer is baking in to their own version. There is  a huge thread on the EEVblog forum covering these testers. Some can be modified to be closer to the official version. In fact, with an ISP tool the intrepid hacker can update the firmware to the current rev from [Karl-Heinz’s] repository.

So the final verdict on this tester is that it is a thumbs up with a small caveat. These testers are built down to a cost (and that cost is as close to zero as possible). They’re great for sorting parts, but they’re no substitute for a higher quality measuring device. I’d also love to see a version that supports the original developers.

Abstracting transistors into high-level design

Although it’s not the best way of understanding computers, most people tend to imagine electronic devices as black boxes filled with magic and blue smoke. Even microcontrollers, the most fundamental means of computation, are treated like little black plastic centipedes with metal legs. In a series of blog posts, [Andrew Gibiansky] is tearing down the walls of obfuscation and illuminating the world of transistors, gates, and FPGAs.

The first blog post goes over the idea of electronic circuits as a waterfall; a positive voltage is a reservoir on a mountain top and ground is sea level. This idea is extended to the lowly transistor acting as an electronic switch, able to turn a circuit on and off.

Continuing on to logic gates, [Andrew] covers the NOT, AND, and OR gates before moving on the flip-flops and SRAM. These can, of course, be modeled in Verilog and VHDL – programming languages that abstract the world of transistors and gates into a much more human-readable form.

[Andrew] is far from done with his series of blog posts, but judging from his work so far it seems to be a great resource for untangling the obtuse concepts of gates and memory into the coherent design of a computer.