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.

The adventure continues with a balance-beam amplifier (using two sewing bobbins to wrap the coils on, carbon from an old flashlight and counterweight from old clock gears),  a needle box transformer (necessitating an explanation of Ohm’s law and Thevenin’s Theorem), and arrives at The Vacuum Tube. Of course you can’t understand vac tubes without a discussion of the atom, thermionic emission, and the thermionic diode and triode.

The semiconductor doesn’t get left out in the cold either. Friedrichs takes the time to explain point-contact transistors using germanium crystals taken from old germanium diodes. If that’s not made-from-scratch enough, he has a few chapters experimenting with copper sheets to produce cuprous oxide which is where my interest lies.

Making a Cuprous Oxide Semiconductor Diode

My own cuprous oxide making setup
My own cuprous oxide making setup

I originally bought this book, to make a cuprous oxide semiconductor diode. In the photo you can see my setup during one day of experimenting. The jar in the back contains hydrochloric acid, available in hardware and pool stores as muriatic acid, and hence the splash visor and safety gloves.

The process uses borax (a household cleaner) to first clean the copper. Next the stove element is used to heat the copper along with the acid, forming the desired cuprous oxide layer as well as a cupric oxide on top of that which needs to be removed.

Unfortunately I didn’t succeed in producing any diode-like activity. That is certainly not a failing of the book. I spent only two days experimenting and ran out of time. It’s amazing to me that Friedrichs managed to make these rather involved topics so approachable that I could try this with easy to obtain ingredients. And I do hope to return to it someday.

This is a fantastic book for anyone who wants to get their hands dirty actually building vacuum tubes or who wants to try their hand at a semiconductor transistor or experiment with making any old-school amplifier component. But even if you don’t take on the experiments yourself there is a wealth of knowledge to be learned just by reading the background and watching the approach used for each build. I highly recommend this book. On these topics it is indispensable.

Do you have a similarly awesome book to you to recommend? Let us know in the comments below.



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