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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Home Made Diodes From Copper Oxide

We’re all familiar with semiconductor devices, and we should remember the explanation from high-school physics classes that they contain junctions between two types of semiconductor material. “N” type which in the for-schoolchildren explanation has a surplus of electrons, and “P” type which has “Holes”, or a deficit of electrons.

Unless our careers have taken us deep into the science of the semiconductor industry though that’s probably as close as we’ve come to the semiconductors themselves. To us a diode or a transistor is a neatly packaged device with handy wires. We’ve never really seen what’s inside, let alone made any real semiconductor devices ourselves.

[Hales] though has other ideas. With the dream of creating a paintable semiconductor layer for ad-hoc creation of simple diodes, he’s been experimenting with oxidising copper to make a surface of cupric oxide onto which he can make a contact for a simple diode.

What makes his experiments particularly impressive though is not merely that he’s created a working diode, albeit one with a low reverse breakdown voltage. He’s done it not in a gleaming laboratory with a full stock of chemicals and equipment, but on his bench with a candle, and drops of water. He takes us through the whole process, with full details of his semiconductor manufacture as well as his diode test rig to trace the device’s I/V curve. Well worth a read, even if you never intend to make a diode yourself.

We’ve featured a cuprous oxide diode once before here at Hackaday, albeit a rather fancier device. If this article has piqued your interests about diodes, may we direct you to this informative video on the subject?

The diode looks black, leading me to believe it’s cupric oxide and not cuprous oxide. Feel free to argue that point in the comments anyway – Ed.

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?