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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Etching your own boards really, really fast

Sometimes the planets align and the Hackaday tip line gets two posts that are begging to be used together. Here’s two hacks to etch your own boards at home in just a few minutes.

Toner transfer PCBs on the quick

One way of putting an etch mask on a PCB is with the toner transfer method: print your circuit on a piece of inkjet photo paper using a laser printer, lay that circuit face down on a sheet of copper, and go at it with a clothes iron. This takes a heck of a lot of time and effort, but [Dustin] found another way. He used parchment paper instead of inkjet photo paper. Once the paper was on the board, he rolled it through a laminator. The results are awesome. It’s a very fast process as well – you don’t need to soak your board in water to get the photo paper off.

Etching that’s like wiping the copper away

[Royce] wrote in from the Milwaukee Makerspace to tell us about [Tom]’s etching process that is like wiping the copper off the board.  He used Muratic (Hydrochloric) acid and Hydrogen Peroxide with a sponge to wipe that copper away. The trick in this, we think, comes from the 30% H202 [Tom] picked up at a chemical supply company, but we’re pretty sure similar strengths can be purchased from beauty supply stores. Check out the video after the break to see [Tom] etch a 1 oz. board in just a few seconds.

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