Books You Should Read: Instruments Of Amplification

Psst… Wanna make a canning jar diode? A tennis ball triode? How about a semiconductor transistor? Or do you just enjoy sitting back and following along an interesting narrative of something being made, while picking up a wealth of background, tips and sparking all sorts of ideas? In my case I wanted to make a cuprous oxide semiconductor diode and that lead me to H.P. Friedrichs’ wonderful book Instruments of Amplification. It includes such a huge collection of amplifier knowledge and is a delight to read thanks to a narrative style and frequent hands-on experiments.

Friedrichs first authored another very popular book, The Voice of the Crystal, about making crystal radios, and wanted to write a second one. For those not familiar with crystal radios, they’re fun to make radios that are powered solely by the incoming radio waves; there are no batteries. But that also means the volume is low.

Readers of that book suggested a good follow-up would be one about amplifier circuits, to amplify the crystal radio’s volume. However, there were already an abundance of such books. Friedrichs realized the best follow-up would be one on how to make the amplifying components from scratch, the “instruments of amplification”.  It would be unique and in the made-from-scratch spirit of crystal radios. The book, Instruments of Amplification was born.

The Experiments

Microphonic relays
Microphonic relays, via H.P. Friedrichs Homepage

The book includes just the right amount of a history, giving background on what an amplifier is and how they first came in the electrical world. Telegraph operators wanted to send signals over greater and greater distances and the solution was to use the mix of electronics and mechanics found in the telegraph relay. This is the springboard for his first project and narrative: the microphonic relay.

The microphonic relay example shown on the right places a speaker facing a microphone; the speaker is the input with the microphone amplifying the output. He uses a carbon microphone salvaged from an old telephone headset, housing everything in an enclosure of copper pipe caps, steel bar stock, nuts and bolts mounted on an elegant looking wood base. All the projects are made with simple parts, with care, and they end up looking great.

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How a Muslim Immigrant from Bangladesh Became America’s Master Builder

If the United States has a national architectural form, it is the skyscraper. The notion of building a tower to the heavens is as old as Genesis, but it took some brash 19th century Americans to develop that fanciful idea into tangible, profitable buildings. Although we dressed up our early skyscrapers in Old World styles (the Met Life Tower as an Italian campanile, the Woolworth Building as a French Gothic cathedral), most foreigners agreed that the skyscraper suited only our misfit nation. For decades, Americans were alone in building them. Even those European modernists who dreamed of gleaming towers along Friedrichstraße and Boulevard de Sébastopol had to cross the Atlantic for a chance to act on their ambitions. By the start of World War II, 147 of the 150 tallest habitable buildings on the planet were located in the United States. 

No building style better represented America’s industriousness, monomaniacal greed, disregard of tradition, and eagerness to attempt feats that more established cultures considered obscene. And while those indelicate traits prompted Americans to develop the skyscraper, it was our openness and multiculturalism that brought us our greatest skyscraper builder: a Bangladeshi Muslim immigrant named Fazlur Rahman Khan.

Khan was born on April 3rd, 1929 in Dhaka, Bangladesh (Dacca, British India at the time). His father, a mathematics instructor, cultivated young Fazlur’s interest in technical subjects and encouraged him to pursue a degree at Calcutta’s Bengal Engineering College. He excelled in his studies there and, after graduating, won a Fulbright Scholarship that brought him to the University of Illinois. In the United States, Khan studied structural engineering and engineering mechanics, earning two master’s degrees and a PhD in just three years. After a detour in Pakistan, Khan returned to the United States and was hired as an engineer in the Chicago office of Skidmore, Owings & Merrill (SOM), one of the most prominent architecture and engineering firms in the world.

Though he was born in a nation with no history of highrise construction, Dr. Fazlur Rahman Khan had worked his way to a position where he would revolutionize the field of structural engineering and build America’s proudest landmarks.

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Fork-o-Drumbot: A MIDI Drummer!


We just got word of a great project by [Vito] — A MIDI Drumbot made from an Arduino and scraps from around the house!

After learning some basics of programming microcontrollers way back in high school, [Vito] was excited to start using the Arduino platform. His first thought was to build a desktop milling machine for engraving his own PCBs. But after a bit of research, he soon concluded it might be a bit too ambitious for a first project, so he opted for something a bit simpler — A robot drummer.

Using some cardboard, a few elastics, a plastic fork, a 12V solenoid, an Arduino and a MIDI interface he had created the original Fork-o-Drumbot, able to tap a simple beat, using one note. After this initial success he grew excited to continue along the same vein of recycling things to characterize his entire project. Fast forward a few weeks of blog posts and he now has a fully functional MIDI drummer which even has a cymbal! They were even featured in the local newspaper after performing a duet with a local singer during an art exhibit called the Singing Balconies of Friedrichshain.

Stick around after the break for an extremely catchy rendition of Superstitious by Stevie Wonder, as played by the Fork-o-Drumbot!

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Making punch card programming a snap

About thirty years ago [H. P. Friedrichs] pulled off a hack that greatly improved the process of programming with punch cards. At the time, his school had just two IBM 029 keypunch machines. One of them is shown in the upper right and it uses a keyboard to choose which parts of each card should be punched out. This was time-consuming, and one misplaced keystroke could ruin the card that you were working on. Since you had to sit at the machine and type in your source code these machines were almost always in use.

But wait, the school acquired a dozen of the TRS-80 computers seen in the lower left. They were meant to be used when teaching BASIC, but [HPF] hatched a plan to put them to task for punch card generation. He built his own interface hardware that connected to the expansion port of the new hardware. Using his custom interface a student could create a virtual card deck that could be rearranged and revised to correct mistakes in the source code. The hardware then allows the virtual deck to be dumped in to the punching machine. This broke the bottleneck caused by students sitting at the punch card terminal.

We think that [HPF] sent in this project after seeing the antiquated hardware from that 1970’s calculator. These hacks of yore are a blast to revisit so don’t be afraid to tip us off if you know of a juicy one.

Marvelous Magnetic Machines

[HP Friedrichs] wrote in to tell us about an upcoming book titled Marvelous Magnetic Machines. Ordinarily, we skip over promotional hype. After watching his promo video though, we couldn’t help but share. We want a copy of this book. In this book you’ll find details on how to build a number of different motors from scrap. You can see several variations in the promo video. He also notes that the music was created by himself and some friends a few years ago. If [H.P. Friedrichs] sounds familiar, it is because he’s been sending us fantastic projects since at least 2006.

DIY Diodes

[H. P. Friedrichs], the creator of the Static Bleeder has created his own diodes. Using household chemicals, a film of cuprous oxide was made on a copper pipe cap. Cuprous oxide has been one of the first known semiconductor substances, has a low forward drop but is an otherwise asymmetrical conductor, odd V-I curves, and some neat photovoltaic action. The apparatus seen above is used to bring a piece of lead (in this case, solder) into contact with the salmon-colored cuprous oxide while electrical connections can be made to the binding posts at the front. What are your thoughts on this device?

Static Bleeder

When you are in the middle of the desert, pretty much every solution to a mechanical or electrical problem is a hack. [Sgt.M] who was deployed in Iraq sought out the help of radio guru [H.P. Friedrichs] about a static problem he was having. When dust storms would blow in strange things would happen in camp. Humming and crackling could be heard and [Sgt. M] actually had an electrical arc from a lamp to his hand at a distance of about 2 feet.

[Friedrichs] helped him find the problem. Their antennae were acting as static electricity collectors in the dust. All that dust friction in the dry air constantly built up a charge. The solution was simple, discharge the electricity at the antenna when it isn’t in use. Several solutions are outlined on the page, so check them out.